PART I

THE NATURE

OF LIVING MATTER

BY

LANCELOT HOGBEN

_Professor of Social Biology in the University of London_

The mind that needs to know all things must needs

at last come to know its own limits, even its own nullity,

beyond a certain point.--D. H. Lawrence

LONDON

KEGAN PAUL, TRENCH, TRUBNER & CO., LTD.

BROADWAY HOUSE: 68-74 CARTER LANE, E.C.

1930

Made and Printed in Great Britain by

Butler & Tanner Ltd., Frome and London

To

BERTRAND RUSSELL

FOREWORD

In the summer of 1929 I was asked to speak for thirty-five minutes

in a symposium on the Nature of Life arranged by the officers of the

Physiological Section of the British Association. I soon discovered

that there are many ways of filling up thirty-five minutes devoted to

the consideration of so formidable a topic. Eventually I decided to

make my contribution in the form which appears almost unchanged in the

fourth essay of this book. By that time I had written a volume without

intending to break my silence before attaining my sixtieth year. With

the insertion of some material to elaborate the point of view I had

developed this collection might be described as the rejected addresses.

I owe to my friend Mr. Sewell, who has adopted the same standpoint in a

criticism of æsthetics in course of preparation, the suggestion of the

word _public_ in contradistinction to the _external_ world of Professor

Eddington.

Four contributors to the Symposium on the Nature of Life, General

Smuts, Dr. Haldane, Dr. Wildon Carr and Professor Eddington, had

already published their philosophical views in book form. General

Smuts and Dr. Haldane courteously wrote to me, expressing the hope

that I would criticize their views destructively. I found the time

at my disposal insufficient for stating my own point of view. I have

responded to their invitation in these essays. If certain passages

seem to some of my readers unduly polemical, I have the assurance that

my fellow-contributors will regard this collection as the continuation

of what was a very friendly argument.

I wish to acknowledge my indebtedness to my friend Professor Levy for

criticism and assistance in seeing this book through the press.

L. T. H.

Cape Town,

_April, 1930._

CONTENTS

PART I

VITALISM AND MECHANISM

Summary 1

Introduction 3

I: The Mechanization of Consciousness 33

II: The Atomistic View of Parenthood 56

III: The Nature of Life--an Introduction to the Theory

of a Public World 80

IV: The Concept of Adaptation 102

PART II

DARWINISM AND THE ATOMISTIC INTERPRETATION OF INHERITANCE

Summary 127

V: The Methodology of Evolution 129

VI: The Problem of Species 151

VII: Natural Selection and Experimental Research 170

VIII: The Survival of the Eugenist 193

PART III

HOLISM AND THE PUBLICIST STANDPOINT IN PHILOSOPHY

Summary 217

IX: Biology and Humanism 219

X: Publicity, Reality, and Religion 245

XI: Privacy, Publicity, and Education 266

XII: The Publicist Standpoint and Holism 289

PART I

VITALISM AND MECHANISM

SUMMARY

An uneasy recognition of the conflict between science and common sense

in our generation has rekindled interest in the relation of science to

moral philosophy. In this awakening the physicists have assumed the

leading part. It will not be possible to predict the outcome, until the

contribution of contemporary biology to natural philosophy is taken

into consideration. Some writers have expressed the hope that the

influence of biological concepts may assist to a reconciliation of the

claims of natural science and moral philosophy. This hope is based on a

failure to recognize that modern experimental biology is an ethically

neutral body of enquiry. The merits of a mechanistic or vitalistic

outlook in biology have been too often discussed from an ontological

rather than an epistemological standpoint. Our estimate of the

influence of biological concepts on the future of natural philosophy

must be guided by a recognition of the essential similarity of method

in biology and physics. This similarity is nowhere more evident than

in those branches of physiology which lie most conspicuously outside

the realm of applicability of physico-chemical hypotheses. Traditional

mechanistic physiology has accepted the Cartesian dualism of mind and

matter. The modern physiology of the conditioned reflex has undermined

the distinction between reflex and voluntary behaviour. There is thus

no nicely defined boundary at which physiology ends and philosophy

begins. Biology is annexing regions of enquiry which have hitherto

remained the province of moral philosophy. As a concept of biology

_Mind_ is replaced by _Behaviour_. Since modern biology claims to

interpret the characteristics of conscious behaviour as properties of

physical objects, the advance of biological science cannot be expected

to reinforce the claims of moral philosophy. How far it is possible

to reduce the interpretation of behaviour to purely physico-chemical

hypotheses, we have no means of predicting. At present we can foresee

no limit to progress in that direction. The significant issue is not

the completeness of the mechanistic solution, but whether there exists

any definable method of arriving at a more complete solution than the

mechanistic outlook permits.

* * * * *

“It is our happiness to live in one of those eventful periods of

intellectual and moral history when the fast-closed gates of discovery

and reform stand open at their widest. How long these good days may

last we cannot tell. It may be that the increasing power and range of

scientific method with its stringency of argument and constant check

of fact may start the world in a more steady and continuous course of

progress than it has moved on heretofore. But if history is to repeat

itself according to precedent, we must look forward to stiffer, duller

ages of traditionalists and commentators, when the great thinkers of

our time will be appealed to by men who slavishly accept their tenets,

yet cannot or dare not follow their methods through better evidence

to higher ends. In either case it is for those among us whose minds

are set on the advancement of civilization to make the most of present

opportunities that, even when in future years progress is arrested, it

may be arrested at a higher level.”

Tylor’s _Primitive Culture_

INTRODUCTION

§1

No one who is familiar with contemporary thought can have failed to

recognize two characteristics which have emerged into prominence during

the past two decades. With increasing elaboration of its logical

technique, science has been brought into apparently irreconcilable

conflict with common sense. The result is that scientists, uneasy

in the realization of this conflict, are seeking to establish a new

working relation between science and philosophy. This _rapprochement_

has been brought about especially through recent progress in physics.

It will not be possible to predict its outcome so long as the physicist

claims to speak for science as a whole. In this introductory essay I

propose to discuss in a somewhat discursive and preliminary way how far

the conflict between science and common sense is apparent rather than

real, and to indicate the special need for reviewing the progress of

modern biology in its philosophical bearings.

At the present time few biologists are anxious to court publicity

in the field of philosophic controversy. Those who do so are rarely

numbered among the ranks of those who are still actively contributing

to contemporary progress in biological enquiry. Those who are actively

contributing to the advancement of biological knowledge show little

disposition to commit themselves to far-reaching generalizations.

There has emerged from the morass of speculation associated with the

rise of the evolutionary hypothesis a recognition of the paramount

importance of painstaking quantitative study of limited aspects of

vital phenomena. This attitude is a salutary one. It does not signify

that biology is passing through a phase of stagnation. On the contrary

current biological discoveries contain the germ of philosophical issues

which may prove to be as revolutionary as Relativity and as repugnant

to common sense. In the essays which follow I shall confine myself

to accredited experimental data. I do not pretend that all or even

a majority of biologists will agree with my interpretation of their

philosophic significance.

There is no novelty in asserting the need for incorporating the

contribution of biological science in a modern philosophical outlook.

Herbert Spencer and the Evolutionists prepared the ground fifty years

ago; but they failed to lay emphasis on the methodological aspect of

biological enquiry. The methods and not the results of biological

science are specially significant to philosophical discussion. In

putting forward my own views upon the nature of life, it is not the

results of biological enquiry, but the methods which I propose to

discuss in the first series of essays in this volume. In contrasting

the methods and concepts of physical and biological science, I shall

sometimes draw inferences which will not commend themselves to the

judgment of biologists for whose contributions I entertain a lively

respect. I shall not be surprised to be told that my forecast of the

outcome of biological enquiry is pretentious, and that my philosophical

conclusions are in conflict with common sense.

At an early age I abandoned the conviction that scientific hypotheses

must conform to the requirements of common sense. When I was a boy,

there used to be in Portsmouth, the town of my nativity, a public

figure by name Ebenezer Breach. Mr. Breach was a philosopher. To be

precise he described himself as “Natural Astronomer and Poet.” In that

he belittled his gifts. Of his poetry I shall say nothing, save that he

stated the qualification “poet by Royal Patronage” in his fascinating

brochure _Twenty Reasons against Newtonianism or The Universal

Challenge to Unnatural Science_. This was sold for the modest price

of twopence sterling. As his contribution to modern thought may be

unfamiliar to many cultivated people who were not born in Portsmouth, I

propose to quote the first of his twenty reasons as representative of

the system he develops:

“Because the earth has no axis, therefore nothing on which to

revolve, an imaginary mathematical line is substituted. But no

solid body could revolve on an imaginary axis or line. It is an

imaginary cause which can only produce an imaginary effect, so all

that follows the cause must be imaginary. If anything be placed on

the top of a revolving body it will fly off at a tangent.”

From this you might infer, wrongly it happens, that Mr. Ebenezer

Breach earned a comfortable livelihood as Regius Professor of Moral

Philosophy in an authentic University. He had in fact chosen to bear

witness to the hope that was in him by the only alternative which a

harsher economic destiny had imposed. Every Saturday night he addressed

a handful of half-intoxicated seamen, tired commercial travellers,

adventurous nursery maids and irreverent pupil teachers foregathered

on the sea-front. There he occasionally succeeded in selling a copy

of the _Twenty Reasons_, and beyond this obtained, as far as I am

aware, no reward in the life that now is. In spite of his erudition and

distinction of person, Mr. Breach, the prophet of common sense, did

not make many converts. He was less successful in his popular appeal

than an evangelical competitor who used to minister to Portsmouth beach

before a banner whose legend stated, “the wages of sin is death.”

This banner I can still recall as, in its way, a work of art. On the

foreground were displayed the theatre, race-course, public-house,

dancing saloon and gaming tables along the edge of a precipice over

which poor folk in a semi-incandescent condition were tumbling into a

lake of brimstone and fire. It invariably drew a large crowd. I had

early imbibed the notion that science like Sunday travelling, whist and

dramatic entertainment is worldly, so that the gospel of Mr. Breach,

who condemned science on account of its essential unworldliness,

presented a new and arresting point of view. On the whole the

inhabitants of Portsmouth were more interested in their souls and what

would become of them after death. Mr. Breach had another competitor

with more peculiar views about the soul and about life. As far as I

can remember he held that the brain secretes consciousness in much the

same way as the liver secretes bile, and he asserted that the soul

was the shadow cast by the machine. My nurse held very definite views

about his domestic life. He was a materialist, and in all probability a

polygamist, if not worse. Mr. Breach who was a bachelor, the evangelist

who was certainly not a polygamist, and the Secularist who was

undoubtedly a bad man all agreed in one particular. Each believed that

the gospel he proclaimed was common sense.

Of the Flat Earth faith Mr. Ebenezer Breach is the only Confessor and,

financially speaking, Martyr I have been privileged to encounter. I

cherish the recollection of his secular ministrations for a reason

which is eminently relevant to everything which I propose to say about

the bearing of current biological concepts on philosophical discussion.

At an age when, to my way of thinking, Punch and Judy were the only

serious rivals to the magnetism of his stupendous intellectual

gifts Mr. Breach stands out in the sharp relief of retrospect as the

Forerunner of the coming conflict between science and common sense.

I have already remarked that the uneasy recognition that science

conflicts with common sense has been the keynote of philosophical

controversy during the past decade. Curiously enough some scientists

seem to regard this as a grave disability on the part of science.

They feel compelled in consequence to adopt an apologetic attitude

to the claims of traditional philosophy. Perhaps this is because the

protagonists of science in the nineteenth century made it their proud

boast that science is nothing more than organized common sense. They

therefore felt that they had the man in the crowd on their side. Even

Herbert Spencer, prophet of evolution, when evolution was still a

subversive doctrine, could soberly declare that “the ultimate truth of

a proposition is the inconceivableness of its negation.”

Neitzsche includes this quotation in the _Will to Power_ as one of his

“inscriptions over the porch of a modern lunatic asylum.” It is only

necessary to mention the word Relativity to indicate how impossible it

would be for a natural philosopher to express himself in similar terms

to-day. The situation which has been created by progress in modern

physics is not without parallel in human history. It is true that

the new theories have employed an immensely elaborate and difficult

logical technique. How far they can be simplified it is at present

impossible to predict. Newton’s fluxions were unfamiliar to his

contemporaries. The author of the _Principia_ devoted a good deal of

time to a geometrical presentation of his ideas, in order to make them

accessible to his generation. For more than a century after Newton’s

death the calculus remained a preserve for mathematical specialists.

To-day a knowledge of the calculus requisite to an elementary

understanding of the theory of elliptical orbits lies within the scope

of the first year’s work at a university, if it has not been acquired

in the higher forms of a good school. It is conceivable that the

mathematical development of modern physical theories will be simplified

in the course of time. In that sense the esoteric stage through which

physics is now passing may be a temporary phase. The essential feature

of the conflict between common sense and physical science in this

generation lies in the unfamiliarity of the new concepts. The conflict

between common sense and the new biological concepts shares the same

characteristic.

In Bernard Shaw’s _St. Joan_, La Tremouille asks: “Who the deuce was

Pythagoras?” “A sage,” replies the Archbishop, “who held that the earth

is round and that it moves round the sun.” “What an utter fool,” says

La Tremouille, “couldn’t he use his eyes?” La Tremouille here calls

attention to a fact that was overlooked by Herbert Spencer, by Mr.

Ebenezer Breach and by those Relativist philosophers, who, being unable

to convince the man in the crowd, indulge in the luxury of wondering

whether the claims of scientific method have been pushed too far.

Common sense is another name for what good citizens are prepared to

accept without argument. Scientific ideas only conflict with common

sense so long as they are still new and unfamiliar. Mr. Breach was in

advance of his time in daring to criticize the Newtonian system. He was

behind his time in thinking that Newton’s position could be assailed

successfully with the weapons of common sense. The essential rightness

of the Newtonian system had already become incorporated in British

middle-class respectability. To the rising generation suckled on Mr.

Wells’ _Outlines_ evolution is common sense. Two generations have

elapsed since, as La Tremouille would say, any fool who used his eyes

could see that a bishop was a product of special creation. The man in

the crowd has no clearer notion of the logical status of the doctrine

of descent than had his grandfathers who implicitly accepted the story

of the Fall.

The phenomenal success of those who set out to popularize the Theory

of Evolution makes it easy to overlook the circumstance that evolution

was wholly repugnant to common sense within the memory of those who

are still living. The outburst of public controversy which greeted its

announcement has no parallel in this generation. In consequence its

impact upon traditional philosophy has been far less apparent than

its influence upon religious dogma and social theory. The younger

generation of biologists cannot recapture the first fine raptures of

enthusiasm which their elders experienced. The prevailing attitude is

to welcome a return to the complacent dualism of pre-Darwinian days,

when scientists did not meddle with philosophy and metaphysicians

conceded to scientists the right to go to the devil in their own

way. Although this view is widely held, I do not believe that the

philosophical implications of evolution have ever been thoroughly

explored; or that it was possible to do so, while the study of animal

behaviour was still dominated by the language of introspective

psychology. By explaining the secular origin of philosophers Darwin

bequeathed to us the task of elucidating the anatomy of philosophy.

In the opening years of the present century, science had already

lost that truculence which one associates with the generation of

Huxley and Tyndall. It had surrendered its tradition of fearlessness

and candour. Academic philosophy, liberal theology and utilitarian

science went their placid ways without mutual interference. Bergson,

a philosopher more widely known than Mr. Ebenezer Breach, had cast

a pebble of _belles lettres_ into the mill-pond of compromise. The

indifference with which it was greeted by those engaged in the task

of placing the evolutionary problem upon a secure foundation of

experimental data is a measure of the esteem which they entertained

for it. It has been interpreted as assent by some contemporary writers

who are not themselves biologists. In _Science and the Modern World_

Dr. Whitehead even speaks of Bergson’s “instinctive grasp of modern

biology.” A modern biologist engaged in the study of behaviour would

refer with greater caution to Madame Blavatsky’s instinctive grasp

of modern astronomy or Mahatma Gandhi’s instinctive grasp of modern

economics. He would regard the instinctive grasp of any branch of

scientific knowledge with more suspicion than approval. No biologist

has undertaken the task of examining the philosophical implications

of Darwin’s doctrine in the light of contemporary progress in the

experimental analysis of living matter.

§2

Under the influence of Hegel, academic philosophy left the scientist

to his own devices. To-day the physicist has again driven the idealist

philosopher out of his retreat. He has compelled him to take account of

a conceptual world which we all recognize whenever we consult a railway

time-table or book a passage in an ocean liner. Secure in the prospect

of fresh philosophical victories, the astronomer surveys the world with

a blind eye to the microscope, and magnanimously dictates the new

territorial frontiers of science and moral philosophy to the advantage

of the latter. It has been customary in the past, and therefore common

sense, to assume that the issues with which moral philosophy deals are

more fundamental than those which fall within the scope of natural

science. It is an assumption which, whatever its meaning, does not

hamper the advance of pure physics; but the biologist is not bound to

accept this convention when it restricts his own field of enquiry. A

philosopher is a particular kind of organism. Philosophy itself might

therefore be regarded as an aspect of the behaviour of a piece of

living matter. The study of the properties of living matter is the

province of the biologist. From this point of view the study of biology

is more fundamental than the pursuit of moral philosophy.

The physicist brings to the discussion of philosophy the discipline

of an older branch of enquiry with a more elaborate logical technique

than that of biology. His claim to speak for the whole field of science

should be scrutinized with a critical eye. I am sure that Professor

Eddington will agree with me, when I say that the biologist has a

specific contribution to make to what he has aptly called the “world

symposium.” I am also confident that many biologists will agree with

me, when I state that the contributions of the Relativist philosophers

rarely display a profound understanding of the kind of problems

biologists are now attempting to solve, and the way in which the modern

biologist sets about his task. A quotation from Mr. Sullivan’s _Bases

of Modern Science_, a stimulating and provocative book, will illustrate

my meaning. Mr. Sullivan, whose physics I do not venture to criticize,

states: “The primary concepts in terms of which the science of physics

is constructed... have to be supplemented by others in the science of

chemistry, and for the sciences of life and mind, are so far from being

sufficient, that they have hardly yet been found to be relevant.” Half

a century has passed since the concept of chemical affinity was annexed

by thermodynamics, and the most conservative physiologist could hardly

refrain from ridiculing the latter part of this quotation. Professor

Eddington himself has adopted the “Principle of Indeterminacy” as an

_ad hoc_ hypothesis in a limited field of enquiry. From it he proceeds

to draw conclusions about human responsibility and the doctrine of free

will. These are topics which lie nearer to the province of biology than

physics. It would be well to await the verdict of biological science

before accepting inferences of so far reaching a character as those

which Professor Eddington has advanced.

By emphasizing the conflict between science and common sense Relativity

has engendered a new interest in the relation of science to moral

philosophy. To view that relation in its proper perspective the

concepts of modern biology must supplement the concepts of modern

physics. I am not suggesting that this need is overlooked by those

who are not biologists. Dr. Whitehead has gone so far as to advocate

replacing the traditional physical idea of matter by the biological

concept of organism, or as a modern biologist might prefer to say,

behaviour. When he expresses the hope that this will assist to “end

the divorce of science from the affirmations of æsthetic and ethical

experiences,” it is clear that his conception of the nature of

biological enquiry dates from Herbert Spencer and differs from that

which contemporary biologists would generally be willing to accept.

Owing to the separation of descriptive from experimental biology, a

separation for which the evolutionists were pre-eminently to blame,

a well-informed interest in the study of living matter is more rare

among physicists of our period than it was in the days of Robert Hooke

and Boyle or of Euler, Lavoisier, and Laplace. I am convinced that

very few scientists who are not biologists--perhaps no professional

philosophers--possess a clear notion of the way in which the modern

experimental biologist approaches the study of the organism and the

results at which he aims.

I have already suggested that there are special reasons why the

concepts of biology stand in a more intimate relation to the scope of

moral philosophy than do those of physical science in the restricted

sense. It is difficult to define the meaning of philosophy without

implying a particular point of view about the limitations of human

knowledge. There are as many different definitions of philosophy as

there are different schools of philosophical opinion. From the point of

view of the materialist a Hegelian is a sea lawyer. From the point of

view of the subjective idealist a materialist is not a philosopher at

all. If there is anything which all the two and seventy jarring sects

would agree to regard as a problem of philosophy, it is the Nature of

Life. If we are to avoid making any unjustifiable assumptions about the

nature of knowledge, we must for the present define a philosophical

discussion of the Nature of Life as the most comprehensive treatment of

the problem. It does not necessarily follow that there is any essential

difference between a scientific and a philosophic enquiry in this sense.

When people first hear their own voices recorded by a gramophone, it

is well known that they are often--like myself--a little humiliated,

and generally somewhat surprised. I once had occasion to witness an

instructive incident which occurred in the phonetics department of

the University of Cape Town. A gramophone record of three men engaged

in a conversation was prepared. None of the three participants had

previously listened to a record of his own voice. When the record

was completed each man agreed that the voices of the other two were

faithfully recorded. Each man denied that his own voice had any

semblance to its representation by the recording instrument. This

simple experiment in human behaviour illustrates what I shall later

call the distinction between the _private worlds_ and the _public

world_. It also illustrates a fundamental divergence of outlook which

distinguishes two tendencies in philosophical discussion, and makes

it difficult to give any definition of philosophy satisfactory to all

parties. One school of philosophers defines a good record as a record

which on the whole faithfully conveys the impression of human voices.

The philosopher of the opposing school feels that it ought to be

possible to manufacture a record which will faithfully represent the

voice of his opponent, while at the same time registering his own voice

as he hears it himself, when he is speaking, and would prefer other

people to hear it.

This distinction has an interesting history which will be discussed in

the third series of essays in this volume. Greek speculative philosophy

had its first beginnings in a secular curiosity about Nature.

Science and philosophy were thus one and the same thing to Thales,

to Empedocles or to Democritus. In Greek thought speculation was not

sufficiently disciplined by sustained observation of Nature. For that

reason it gave birth to innumerable conflicting hypotheses which could

never be made the subject of decisive tests. Out of this confusion of

conflicting ideas was born a reaction against science. Philosophy

turned from the slow and tedious task of examining the actual world

to the more facile and pretentious pursuit of an ideal world. In

the person of Plato it forfeited its secular temper. Science was

introduced into modern Europe by the Arabs, who assimilated the secular

curiosity of the Greeks. Ecclesiasticism seized upon the speculations

of the later Greek philosophers to provide a rational basis for

theological dogma. Since mediæval times scientists have submitted

to an arrangement which gives to those who have not studied Nature

the right to supervise the logical status of their conclusions. The

stability of this arrangement has been maintained by the circumstance

that human beings are far more interested in themselves than in any

other material objects. Greek materialism declined, because it could

not satisfy man’s curiosity about himself. The success of its rival

was not due to its ability to settle the problems of human nature and

social conduct. It succeeded because human nature demands a forum for

the ventilation of its grievances. Science has been most successful

in the past in dealing with inanimate things. Only in comparatively

recent times has the phenomenal success of scientific method, fortified

by the secular influence of Darwin’s teaching, encouraged the belief

that it might be applied to the study of man’s behaviour and social

organization. The belief that a philosophical discussion of the Nature

of Life lies beyond the province of the biologist is due to centuries

of subservience to a tradition which has identified philosophy with

the interests of statesmanship and ecclesiasticism. If the method of

science is applicable to the study of how statesmen and theologians

behave, it is legitimate to undertake a discussion of the nature

of life without assuming that the biological standpoint must be

reinforced by the discipline of scholastic philosophy.

There is a further assumption which we need not make in our enquiries

into the Nature of Life. We need not presume like Socrates that all

questions about life are permissible. A proper respect for our own

limitations is as essential to philosophy as to sanity and modesty in

everyday life. It is only possible to formulate questions in the right

way when we already have at our disposal a good deal of information

relevant to the correct answer. This was not recognized by the

materialists of the nineteenth century when they attempted to give a

common-sense solution of the Riddle of Life. To-day it is customary to

refer to materialism as an exploded fallacy. If instead of looking at

the way in which the materialist attempted to answer the man in the

crowd, we examine the way in which he attempted to answer the questions

which he himself propounded, the explosion of the fallacy is not so

encouraging to traditional beliefs. The term materialism, when it is

not employed like Bolshevism as a term of abuse, is loosely applied to

a constellation of beliefs, some of which concern the Nature of Life

and some of which concern the Nature of Knowledge. In the latter sense

materialism implies the conviction that the only genuine knowledge is

that which can be gained by pursuing the method devised by scientists

for the study of what are ordinarily called material objects. If this

conviction is carried to its logical conclusion, a discussion of the

Nature of Life in language which is intelligible to the audience of

Mr. Breach or his Secularist competitor is impossible. The materialist

who attempts a common-sense solution of the Riddle of Life is

inconsistent with his materialism. It is his inconsistency and not his

materialism which is an exploded fallacy. Common-sense materialism,

the materialism which is an exploded fallacy to-day, was based on the

belief that a plain answer to a plain question is the inalienable

birthright of the plain man. Secularist rationalism was the offspring

of Protestant democracy. Protestant democracy is suspicious of the

expert, who is the person who knows that there is a technique of asking

questions in the right way as well as a technique of answering them

in the right way. Perhaps Xanthippe, who has become the symbol of a

nagging wife, realized this profound truth more clearly than Socrates.

Perhaps her short way with introspective philosophers was based on a

considered recognition of human frailty, and experience of children.

An intelligent child of three once asked me to tell her the colour of

Wednesday. To the more sophisticated adult the question is ridiculous,

though I suppose the theosophist would regard it as permissible.

Metaphorically speaking, the habit of asking the colour of Wednesday

is not exclusively confined to children. Thousands of years ago human

beings began to associate particular sounds with objects around them,

so that these sounds became signals for activities. These activities

became increasingly more complex as articulate speech became more

elaborate. Gradually human beings ceased to employ a separate symbol

for every object around them. They began to condense and economize,

abstracting separate properties. It became no longer necessary to

have separate words for white cow, black cow, white horse and black

horse. In effecting this economy it was inevitable that new words with

no clear relation to experience were often invented. Common language

the world over is burdened with words which effect no economy of

discourse. Anyone who has not realized this may perform the simple

experiment of asking six educated people to define in writing on a

folded slip of paper the meaning of the word _sincerity_. With the

coming of civilization man invented a new form of symbolism, the

language of science. In spite of immense social inertia this symbolism

has become more and more important, because of the tremendous power

for controlling nature which it has given us. In the invention of this

new language not only sustained observation of nature, but active

interference with nature, or experiment, is enlisted in the process of

abstraction.

Because common language and the language of science are not the same

thing, there never can be a plain answer for the plain question of the

man in the crowd. There can only be a familiar one. In any restricted

field of scientific enquiry confusion of thought is avoided by the

introduction of new symbols to denote new experience, or a preliminary

re-definition of old symbols, if these are employed. So long as the

chemist is only concerned with the reducing power of a particular

sugar, it is sufficient for him to describe it as dextrose. When he

directs his attention to the optical properties of the sugars he finds

this symbol no longer adequate to define a homogeneous class, and

distinguishes between α dextrose, β dextrose and so forth. When

scientific hypothesis so broadens its channels as to merge into the

general current of human thought, the scientist finds himself dealing

with matters for which there already exists a vocabulary, but one that

has none of the precision of scientific nomenclature, one called into

being by an approach to experience which has none of the disciplined

restraint which scientific method imposes. That is why the practising

scientist is sometimes compelled to treat the conundrums of humanistic

philosophers like the question of the child who wanted to know the

colour of Wednesday. Concerning those things about which we talk most

our language is apt to be least definite.

§3

One of the things about which we talk most is life itself. A discussion

of the Nature of Life presupposes that we mean something quite

definite, when we use the term life. The familiar lines of Mr. Belloc

suggest a helpful analogy to illustrate the nature of a scientific

definition:

“Here you may put with critical felicity

The following question, ‘What is Electricity?’

‘Molecular activity,’ say some.

Others remain silent or are dumb.”

What is electricity?--is a plain question. It is only possible to

give it an intelligible answer when we translate it into the form,

what conditions determine electrical phenomena? A scientific concept

is a label for a class of properties which can be investigated

scientifically. Though this happens to be a cardinal doctrine of

modern logicians, it is also a commonplace of scientific thought,

when undisturbed by ulterior considerations. It is a commonplace

which is constantly overlooked by biologists as well as laymen in a

discussion concerning the nature of life. The temptation to overlook

it is assisted by the custom of spelling nature and life with capital

letters, a practice to which what the Melanesians call _mana_ adheres.

The only intelligible significance of the word Life in scientific

discussion is to denote collectively the properties of living[1] things.

The word life is variously employed in common language. To Mr.

Mantalini life is one demmed {sic} thing after another. Every

biological student is familiar with the experiment of removing a

frog’s heart from its body, maintaining its beat by perfusing it

with a suitable saline medium, arresting its rhythm and restarting

it by changing the constituents of the medium. This can be performed

repeatedly for many hours after the owner of the heart is, legally

speaking, dead. The layman confronted with this commonplace of the

laboratory invariably asks with some show of bewilderment, “Is it

alive?” It is extremely difficult to answer him in words he will

understand. He has been accustomed to think of an organism as a whole,

just as we think of solid matter as a whole. Unaided common sense

does not easily grasp the notion that the frog’s heart displays the

characteristic properties of living matter, after the frog, considered

as a whole, has ceased to display those characteristics of living

matter which we associate with whole frogs, when we say that they are

alive.

In biological discussion the nature of life can only be understood

to mean the characteristic properties of living things, how they are

related to one another and to the properties of non-living matter, how

they have come into being. To those who are accustomed to thinking in

abstract nouns and capital letters this way of defining life will seem

rather like the well-known definition of an archdeacon as a man who

discharges archidiaconal functions; but if life is only a convenient

label for the properties of living matter, we have foreshadowed an

important conclusion. Those who declare that materialism is an exploded

fallacy are usually those who deplore the judicial separation of

science and moral philosophy. If they entertain the hope that biology

is likely to effect a restitution of conjugal rights, they evidently

imply that life to the biologist means something more than the

properties of living matter. They assume that a biological concept of

life contains other implications of its use in common language.

The source of this confusion is easy to understand. The biologist

can no more avoid using the word life than the physicist can avoid

using the word matter in a loose and arbitrary sense in everyday

conversation. Whatever meaning the biologist may attach to the term

life, when he is exercising his domestic and political activities,

there is only one legitimate manner in which he can employ it in

his capacity as a scientist. Much discussion between the opposing

schools of vitalists and mechanists is utterly barren, because this

fundamental issue is not clearly defined at the outset. The vitalist

can legitimately attack the mechanist by pointing out that living

things have characteristic properties other than those which the

mechanist attempts to analyse. If he does so, he must specify what such

properties are. In the laboratory the biologist carries out his work

on the same lines, whether he calls himself a vitalist or a mechanist.

On the platform he may, and frequently does, overlook this. The layman

may thus acquire a disproportionate estimate of the extent to which

biologists differ among themselves about fundamental issues.

That biologists are still less unanimous than chemists in the hope of

resolving, in more universal terms, concepts traditionally restricted

to their own fields of enquiry, may be attributed to the complexity of

their subject matter. Biology is a younger science, and a vast amount

of purely descriptive work was necessary, before it was possible to

formulate the mechanical problems which living matter presents. This

task requiring considerable specialization in the descriptive study

of the exclusively geometrical aspects of the configuration of living

systems unhappily became divorced from the more fundamental issue of

biological enquiry. The physical analysis of the properties of living

matter is a problem necessarily spatio-temporal in its extension,

experimental in its method, and quantitative in its grammar. The

spectacular success of evolutionary speculation during the nineteenth

century preceded the birth of quantitative and experimental researches

on inheritance and variation, giving descriptive biology a reflected

glory on account of the far-reaching cosmological consequences of the

doctrine of descent.

By encouraging the hope of reconstructing the pedigree of mankind,

Natural Selection widened the gulf between descriptive and experimental

enquiry; and provided a satisfactory modus vivendi for two diverging

and independent schools of research. Anatomy claimed the relation of

one type of living being to another. Physiology concerned itself with

the relation of living matter to inanimate objects. During the present

generation evolutionary problems have emerged to the forefront of

experimental enquiry. Heredity and variation are no longer axioms with

which the taxidermist and the osteologist can conjure unchallenged.

Experimental biologists are grateful to those who have compiled

the Who’s Who of the Animal Kingdom. They refuse to concede that

the execution of this task implies a profound understanding of the

principles of political economy. Naturally the anatomist and the field

naturalist view the change with a jealous and suspicious eye.

Biologists agree among themselves in recognizing that the approach to

the organism as a physical object has led to many valuable discoveries;

and that the application of physical methods to the study of the

organism permits us to make many predictions about the behaviour

of living systems with as much confidence as we have in predicting

other secular events. In so far as recent investigation has probed

into phenomena which it has been customary to place beyond the limit

of applicability of physical methods and concepts to the analysis

of the properties of living matter, it is not surprising that many

biologists have failed to take stock of the situation. They may simply

deny that certain aspects of the behaviour of organisms can be treated

successfully by the traditional methods of experimental physiology. If

they do, it should be sufficient to set forth the new evidence at our

disposal. When they go further and assert that certain characteristics

of living things properly belong to the sphere of traditional

philosophy, it is permissible to entertain the suspicion that they

share the all too human desire to be _certain_ rather than to _know_.

The chief source of disagreement between different schools of opinion

in any discussion of the Nature of Life arises from the difficulty

of defining another concept which is intimately connected, but not

necessarily co-extensive with, that of life itself. It has been

customary in the past to assume that the concept of _consciousness_

defines a field in which the methods of experimental physiology break

down and require to be supplemented by the method of introspection. In

so far as it bears on the Nature of Life this implies the possibility

of identifying and specifying in living systems characteristics to

which the term consciousness directs attention. It is impossible to

avoid disagreement in connexion with this concept without recognizing a

fruitful source of confusion. The statement “I (N or M) am a conscious

being” has a formal relation to the statement “All men are conscious

beings” like the analogous statement “Mr. Bertrand Russell is a

conscious being,” so long as it is understood that I and Mr. Bertrand

Russell are both single valued and members of the class “men.” From

this it follows that any implication of the first proposition which is

not implicit in the second defies logical analysis and therefore eludes

philosophical enquiry. For the purpose of philosophical discussion “I

am a conscious being” contains nothing that is not implied by saying

that “all men are conscious beings.” I shall use the term _public_

to signify this way of looking at the concept of consciousness. Any

residuum of the first proposition which cannot be formally identified

with the third and shown like it to be included in the second and

more general proposition is a _private_ affair of the individual.

If we find that modern physiology has undertaken to investigate

those characteristics of the behaviour of living systems associated

with the term consciousness in its public sense, a new horizon of

philosophical discussion is unfolded. If physiology is more successful

than introspective philosophy in defining predictable conclusions about

living behaviour, we have no need to go outside the data of physiology

for the materials of a comprehensive discussion of the Nature of Life.

A philosophical discussion of the Nature of Life will only be more

comprehensive than a biological discussion of the Nature of Life in

the sense that more attention will be paid to the methods of enquiry

adopted.

Between two extreme schools of opinion existing at the present day the

issue, in so far as it is a tangible one to the practising biologist,

is thus defined by Dr. Haldane in his recent Gifford Lectures.

“We can of course leave the characteristic peculiarities of

conscious behaviour out of account, and regard persons from a

purely physical and chemical point, as weighing so much, as

yielding certain amounts of various proteins and other chemical

substances, distributed in a certain way, and as in various ways

continually converting potential into kinetic energy. This mode

of regarding persons is of great practical use for engineering

and other purposes, _but tells us nothing, however far we may

extend it, regarding the distinctive_ characters of conscious

behaviour...” (italics inserted).

In this passage Dr. Haldane is perfectly definite in stating where,

as he believes, the methods of traditional physiology cease to

be applicable. It is peculiarly felicitous that he uses the term

conscious behaviour rather than consciousness in this connexion. If

we find reason to believe that “conscious behaviour” can be analysed

with reference to a space-time framework by the methods of physical

science, Dr. Haldane’s attack on the mechanistic position falls to

the ground except in so far as he can refuse to capitulate until the

problem has been reduced to a question of pure physical chemistry. In

the succeeding essay on The Mechanization of Consciousness I shall

endeavour to show that in our generation the work of Pavlov’s school

has successfully tackled, for the first time in history, the problem of

what Dr. Haldane calls “conscious behaviour” in non-teleological terms.

It has reduced it to the investigation of the conditions under which

new reflex systems are brought into being.

In _Science and the Modern World_ Professor Whitehead states that

the “effect of physiology” on philosophical discussion has been

“to put mind back into nature.” I presume that he is referring to

the traditional distinction between reflex activity and voluntary

behaviour. It is true that physiology has accepted this distinction

which it inherited from the dualism of Descartes; but traditional

physiology never attempted to probe deeply into the nature of

voluntary behaviour. It was content to investigate reflex activity,

and concede the prerogative of discussing the characteristics of

conscious behaviour to moral philosophy. _Experimental physiology

like experimental physics is an ethically neutral science._ If Pavlov

has reduced the problem of conscious behaviour to the same level

of discussion as the problems of reflex behaviour, the traditional

distinction between reflex and voluntary activity has ceased to define

the boundary at which physiology ends and moral philosophy begins. If

the investigation of the characteristics of conscious behaviour can

be brought within the scope of an ethically neutral method, we must

abandon any hope that biology can assist to end “the divorce of science

from the affirmations of æsthetic and ethical experiences.” If the

Relativists can say that modern physics has given materialism its death

blow by referring solid matter to an atomic nexus of conceptual fields

of force which only exist in our consciousness, the physiologist can

add that modern biological enquiry is disintegrating consciousness into

an atomic nexus of reflex arcs. If modern physics has shown that we

can no longer think profitably of solid matter as existing in the way

in which it presents itself to common sense, modern biology is showing

that for the purpose of profitable discourse mind itself does not exist

as the essential unity which it assumes to common sense. If the advance

of science has disposed of the older forms of materialism, it is also

disposing of the traditional forms of idealism and dualism at the same

time.

Biological science no less than physics is opening up new fields

for exploration in philosophy. The new approach to the problem

of “conscious behaviour” involves an intellectual effort no less

repugnant than the non-Euclidean space of the relativist. The new,

in preference to the traditional biological standpoint, owes its

sanction to the same test as that by which relativistic theories must

in the last resort be assayed. A disinclination to discuss “conscious

behaviour” and a tendency to assert dogmatically the possibility of

reducing it to purely chemical concepts has been characteristic of the

mechanistic standpoint in the past. It would seem that to emphasize the

applicability of physical methods to living matter in all its aspects,

a new term, free from this taint, is now needed. _Behaviourist_ has

already acquired certain restricted implications, and for reasons which

will be set forth in a succeeding essay I shall sometimes speak of

the _publicist_ in preference to the mechanistic standpoint. Unlike

the Flat Earth doctrine of Mr. Breach the publicist standpoint in

philosophy is not based on an appeal to common sense.

I began these introductory remarks by calling attention to two

characteristic features of contemporary thought, the uneasy recognition

of the opposition of science to common sense and the renewed search

for a working agreement between the claims of science and of moral

philosophy. In concluding, I would add a third to which I have not

explicitly referred. The scientist brought into collision with common

sense has for the time being lost his former air of self-confidence.

We are told that science does not deal with reality, that the external

world of physics is a shadow world, that the laws of physics are only

statistical generalizations, that scientific hypotheses are no more

than convenient devices to aid us in the practical business of living.

I cannot but feel that the solemnity of these assertions is out of all

proportion to their novelty. I cannot discover why recent developments

in physics constitute a specially cogent reason for reiterating them

at the present moment. I am disposed to believe that some of the

younger generation who have been familiar with the writings of Mach,

of Pearson, of William James and of Bergson, since they first began to

think about the nature of scientific knowledge, must share with me a

sentiment of surprise, when told that living scientists ever seriously

put forward those extravagant claims which, as we are now assured,

received their death blow from the theory of a relativity and the new

quantum mechanics. The apologetic attitude so prevalent in science

to-day is not a logical outcome of the introduction of new concepts. It

is based upon the hope of reinstating traditional beliefs with which

science was at one time in open conflict. This hope is not a by-product

of scientific discovery. It has its roots in the social temper of

the period. For half a decade the nations of Europe abandoned the

exercise of reason in their relations with one another. Intellectual

detachment was disloyalty. Criticism of traditional belief was treason.

Philosophers and men of science bowed to the inexorable decree of herd

suggestion. Compromise to traditional belief became the hall-mark of

good citizenship. Contemporary philosophy has yet to find a way out of

the intellectual discouragement which is the heritage of a World War.

The physicist has abandoned teleology in his own field. He has banished

the spiritual values from the domain of his enquiries. He now looks

to the biologist to shoulder the task of proving that the universe is

consonant with our notions of ethical propriety. I shall endeavour to

show that the progress of modern biology gives no justification for

the belief that such a compromise is possible. In approaching this

task my aim is not primarily to advocate the mechanistic conception of

life or to criticise the vitalistic standpoint. Controversy between

writers of the mechanistic and vitalistic schools has too often focused

attention on whether a complete solution of the Nature of Life can be

found within the mechanistic framework. The more significant question

is whether any solution can be obtained outside the mechanistic

framework. It may be interesting to know how far the biologist has

progressed in his enquiry into the Nature of Life. Philosophically it

is more significant to understand what methods of investigation have

permitted him to advance towards an admittedly partial solution of his

problem. To show that the mechanistic conception of life is inadequate

is one thing. To show that any alternative and more comprehensive view

can be gained by pursuing methods other than the traditional methods

of experimental biology is a more difficult task. It appears to me

that the mechanist can admit every criticism which the vitalist brings

to bear upon his case without weakening its essential strength. If

we commence our enquiries with the assumption that it is possible to

know everything, we shall be disappointed to find that the mechanistic

conception of life does not--and probably never will--find an answer

to every question which we may be tempted to propound. In that

disappointment lies the false security of the vitalistic standpoint.

It was the peculiar merit of Hume’s philosophy that he rejected the

necessity of making this assumption.

In assessing the respective contributions of the biological and

physical sciences to the construction of a Public World, we are

investigating the existence of certain characteristics common to all

branches of natural science. The method of science is not static. It

is ever growing and expanding, incorporating new territories within

its empire. For this reason formal definitions unfortified by an

examination of the historic past tend to be superficial and barren.

The origins of even the most exact sciences are deeply rooted in

the soil of magic. At any stage in the progress of human knowledge

particular features may be evident in more than one branch of enquiry.

As time goes on fresh similarities present themselves. The exact line

of demarcation between the already scientific and what is not as yet

scientific is therefore somewhat arbitrary. No definition of scientific

method is adequate unless it implies the recognition of a developmental

sequence in which new characteristics emerge successively into

prominence.

In the natural sciences, as customarily defined, it is essential that

the data shall be publicly accredited by the testimony of independent

observers. The observation and recording of publicly accredited data

is not in itself regarded as an adequate criterion of scientific

study, unless the data are arranged or classified in a particular way.

Such classification makes it possible to draw inferences which extend

beyond the range of the original data. The validity of the relations

implied in a particular classification is referred to their capacity

to permit us to predict verifiable conclusions. In practice it is

necessary to classify the data of a problem in a variety of ways before

it is possible to arrive at the type of classification which yields

relations satisfying this criterion of validity. This circumstance

assists us to draw a rough distinction between a type of enquiry

which is maturely scientific and one which is in process of becoming

scientific. In the older and more firmly established branches of

science, it is evident that severe economy in the initial assumptions

promotes the construction of hypotheses which are valid in the sense

defined. Ethical values have been eliminated altogether. The same

characteristics are increasingly recognized in newer departments of

scientific investigation.

When every criticism of the limitations of scientific method has been

accepted, the belief that philosophy can provide a means of solving

the problems which lie outside the realm of scientific enquiry still

remains to be proved. In the essays which form the third series of this

volume, I shall endeavour to discuss whether an enquiry into the nature

of reality has any intelligible meaning. With Hume I doubt whether it

is possible to attach any significance to deciding whether scientific

beliefs are a faithful representation of “reality.” Scientific beliefs

are specially characterized by their communicability, or, to use the

term which I shall employ more frequently, their _publicity_. The

fundamental problem of a philosophy which does not presuppose what

it sets out to establish is to find what characteristics of beliefs

make them communicable. It is by examining these characteristics

that we can hope to decide whether the discussion of our ethical and

æsthetic predilections can yield conclusions which have the same kind

of communicability as scientific beliefs, and, if that is possible,

in what manner such discussion must be conducted. I shall endeavour

to show that there is a confusion of meaning involved in discussing

whether the experiences with which science deals are more or less real

than the experiences which moral philosophy has claimed for its parish.

The more modest task of deciding whether the conclusions of science

have more or less communicability than ethical and æsthetic beliefs is

not a problem which necessarily eludes unprejudiced investigation.

I have indicated that an enquiry into the nature of life and the

nature of consciousness presupposes the necessity of formulating the

problem in the right way. This task is a necessary preliminary to

the analogous question, what is philosophy? The firefly emits light.

When we say that we understand what animal light is, we mean that we

understand what processes are involved in the production of animal

light. The method of science can lay bare the structures in which

luminescent materials are secreted and the physical transformation

of their chemical energy into visible radiation. Animal light is an

unusual characteristic of a species of insect known as the firefly.

The light of reason is a peculiar characteristic of certain human

beings known as philosophers. We can only say that we truly understand

philosophy or the light of reason, if we understand the processes which

confer upon philosophers their unusual characteristics. A philosopher

brought into being by the process of natural generation develops in an

environment which includes inanimate objects and other human beings.

He reacts to his physical environment by growth and to his social

environment by learning. If the method of science can assist us to

elucidate the processes of growth, learning and natural generation,

science can assist us to understand what philosophy is. The anatomy

of philosophy and the physiology of philosophers are inseparable. We

need not be discouraged in pursuing this line of enquiry, because the

answer which science can give us at present is incomplete. It is the

chief glory of science that its answers are always incomplete. The

pitiful failure of introspective philosophy resides in the finality of

its answers. Perhaps the most permanent influence of Relativity in the

history of philosophy will prove to be the challenge it issued to the

finality with which Kant enunciated the concepts of space and time.

I. THE MECHANIZATION OF CONSCIOUSNESS

“Now, in conclusion, the Method which teaches adherence to the

true order and an exact enumeration of the conditions of the

thing sought includes all that gives certitude to the rules of

arithmetic.”--Descartes, _Discourse on Method_

§1

The onus of proving that all the properties of living matter can be

reduced eventually to problems in physical chemistry or, on the other

hand, of denying that such will ever be accomplished, may be laid on

the shoulders of those who commit themselves to rash affirmations and

denials. If this were the only matter to decide, a discussion of the

merits of the mechanistic conception of life could reveal nothing more

than a temperamental difference between the disputants. A temperamental

difference does exist. The mechanist has a cheerful attitude to

knowledge and refuses to capitulate to the fear of the Unknown: the

vitalist, a sadder but not necessarily wiser type, finds balm in the

limitations and failures of human effort. The average biologist, who

has little sympathy either for the heroic or the desperate point of

view, maintains a detached scepticism.

Such scepticism has much to commend it; but scepticism no less than

piety can be employed as an excuse for mere intellectual laziness.

Between those who advocate the mechanistic conception of life and those

who reject it, there is a divergence of outlook more fundamental than

usually appears in the course of controversy. Whether the same set of

hypotheses will ultimately serve to interpret the properties of living

and non-living matter may be left to the arbitrament of time. For

practical purposes a decision one way or the other makes very little

difference to the course of biological enquiry. The fundamental unity

of scientific method in chemistry and physics is not invalidated by

the fact that some phenomena can only be dealt with successfully in

thermodynamical terms, while yet others yield only to treatment with

the aid of kinetic and molecular hypotheses. It is less important to

know how far the properties of living matter can be reduced to physical

chemistry than to decide whether the logical structure of biological

enquiry is essentially similar to or different from that of physical

science. This is an issue of the most far-reaching consequences, not

merely for philosophy but for biology as well. Though rarely stated

explicitly, it represents the basic divergence of standpoint between

the mechanist and the vitalist or holist. It is not merely a matter of

taste or temperament: it is profoundly relevant to the way in which

biological enquiry continues to develop. In this matter scepticism can

only be justified by disinclination to face uncomfortable conclusions.

If the logical structure of biological enquiry is essentially similar

to that of physical science, we must entertain the possibility of

interpreting the whole domain of living matter without departing

from the principle of ethical neutrality. This is not a pleasant

possibility to admit; and it is hardly surprising that few biologists

are enthusiastic in committing themselves with regard to it. If we

find that there is no fundamental difference between the logical

structure of biological and physical science, we cannot follow Dr.

Whitehead in reviving the hope that scientific enquiry will eventually

yield conclusions about the universe in conformity with our ethical

predilections. If, without modifying the structure of its logic,

biological science is capable of annexing as its parish the entire

survey of living matter, there remains no nicely defined boundary

at which science ends and philosophy begins. Philosophical enquiry

must then abandon its pretensions to arrive at conclusions about

the universe unaided by scientific discovery. It must restrict its

operations to an examination of the logical structure of beliefs. It is

therefore remarkable that the biological standpoint has been so little

explored in contemporary criticism of traditional philosophy.

During the past two decades there have been three outstanding

developments in biological research, the work of A. V. Hill and

Meyerhof on the chemical mechanics of muscle, the extension of Mendel’s

hypothesis by Morgan and his colleagues at Columbia, and the study of

the conditioned reflex by Pavlov’s school. Of these the first alone

represents an advance in the actual reduction of vital processes to

physical chemistry. Yet no aspect of biology could be selected more

appropriately than Morgan’s hypothesis to illustrate its logical unity

with the study of chemistry. The study of the conditioned reflex

has not as yet enlisted the resources of physical chemistry to any

noticeable extent. Nor does it employ a logical technique as elaborate

as that of the modern chromosome hypothesis. Its importance lies in

the fact that it has emancipated biological study from the Cartesian

dualism with its implicit assumption that method of enquiry applicable

to one aspect of the properties of living matter is of a totally

different kind from that employed in dealing with the remainder.

To estimate the significance of this advance it is necessary to start

with a clear statement about the meaning of a word. The term _reflex_

is used by dentists, politicians and faith healers with a variety of

implications irrelevant to the biologist. To exclude these irrelevant

associations it is best to be concrete. Suppose that we decapitate

or destroy the brain of a frog, and suspend it, legs downwards, in a

vertical position. On raising a vessel of warm--about 40° C.--water,

until the tips of the toes touch the surface, the legs of the animal

are withdrawn after a short interval. This event takes place regularly

and similarly under the same conditions. It is as definite and

predictable a property of secular objects as is the precipitation of

barium sulphate on mixing a solution of barium chloride with a solution

of sodium sulphate. It is, if you care to express it in that way, a

physical reaction between warm water and frog toes. In biological

nomenclature it is a reflex.

The word reflex is not used in biology to denote every change that

occurs in living matter. To clarify its meaning further we must

consider how such a phenomenon can be studied more intimately. To the

biologist it presents two types of problem. One is that of analysing

the constituent parts of the reaction, and is analogous to what the

chemist does, when he determines the solubility and dissociation

constants of barium sulphate, barium chloride, sodium sulphate and

sodium chloride to define more precisely what occurs during the

reaction with a view to elucidating conditions under which it may be

expected to occur. In the biological example that we have taken the

first stage involves the purely spatial (or anatomical) examination of

the reaction. It may be noted in this connexion that anatomy in its

initial phase was an experimental science, and only became a catalogue

in its dotage. We observe that we are dealing with a localized response

to a localized agent involving a spatially localized structure the

nervous system. We can in fact obtain the reaction from a preparation

from which every structure but the skin of the toe, the nervous system

and the muscles of the leg have been removed. From this point we

proceed by a study of the temporal relations of the phenomenon, first

undertaken by Helmholtz, to show that a disturbance is propagated

at a measurable, predictable and modifiable rate from the seat of

application of the agent to the seat of the visible reaction. The

further analysis of the problem from the physico-chemical standpoint,

an essentially modern development, will be referred to in a subsequent

essay. We have now obtained the current definition of a reflex as a

localized response to a localized stimulus, involving the intervention

of the propagated disturbance known as the _nervous impulse_. Erroneous

ideas implied in the common use of the term reflex arise chiefly in

connexion with the second aspect of the study of reflex phenomena. This

is not readily comparable with the investigation of a simple reaction

like the precipitation of barium chloride. It might be compared with

the interpretation of a more complex system such as the oxidation of

oxalic acid in the presence of potassium permanganate and sulphuric

acid, when the behaviour of any two reactants towards one another is

already known. Frogs lift their legs from time to time in civil life,

when they enjoy the use of a head. We may therefore ask what part

do such reflexes, as we can study in the headless frog, play in the

behaviour of the intact animal.

In any reflex displayed by the pithed frog the nervous impulse

traverses a characteristic path. From the skin, the receptive area

affected, it passes by one of numerous fibres of microscopic thickness

to the spinal cord. Such fibres together with others carrying impulses

from the cord to the muscles or glands collectively constitute the

visible nerves. Fibres carrying impulses into the cord divide into very

fine branches in the inner core or grey matter. These fine branches

are intertwined with the ramifications of other fibres passing up

and down the length of the cord. The latter branch at their other

extremities around the fine endings of fibres which pass from the cord

to the glands and muscles. An impulse entering the spinal cord first

therefore passes across the junction or _synapse_ between the fibre

along which it enters the cord and some other fibre running up or down

the cord. Having traversed the latter, it passes across the junction or

synapse between its branched ending and that of some fibre connecting

the spinal cord with a muscle or gland. Reflex action depends upon the

fact that an impulse travelling along a particular fibre can traverse

some synapses more readily than others. This is a physical process,

occupying a measurable time. By the use of certain physical reagents it

is possible to increase the conductivity of the synapses, so that an

impulse entering the cord irradiates to all the muscles of the body.

Strychnine is such a reagent.

The familiar fact that the moth flies towards the candle will serve

to illustrate how the study of a simple reflex, like the withdrawal

of the toes of the pithed frog from warm water, makes it possible to

make predictable conclusions about the normal behaviour of animals.

If the nerves of the frog’s leg are severed, the leg hangs limply.

Normally the muscles of the leg are never completely relaxed. They

are maintained in a state of partial contraction or _tone_, reflexly

determined by a number of agencies which for our present purpose it

is unnecessary to specify. The nerve fibres which run up and down the

length of the spinal cord in the frog cross from one side to the other

at some level, and on this account most reflexes obtained in the pithed

frog, when only one side is stimulated, involve muscular response of

both sides of the body. Insects which move towards the light become

noticeably more limp in darkness. Light reflexly increases the tone of

their muscles. In insects there is little crossing of fibres from one

side of the central nervous system to the other. It follows that, if

light reflexly increases tone, the muscles of that side will be more

contracted, when one eye is illuminated more strongly than its fellow.

This will have the effect of bending the body round in the direction of

the incident beam, until the head is brought into such a position that

both sides are equally illuminated. Having attained this position the

body will continue to move along the direction of the incident beam. If

it swerves to the right or left, it is automatically readjusted.

This interpretation of the proverbial flight of the moth towards the

candle permits us to make a very large number of easily verifiable

predictions. One simple consequence repeatedly confirmed by experiment

on a variety of insects which fly towards the light is the fact that,

when one eye is blinded, they fly in circles. There is no need to

mention the variety of predictable positions which such insects occupy,

when allowed to crawl up rotating cylinders illuminated in various

ways. One other rather interesting result of the experimental analysis

of this phenomenon is worth mentioning. According to the common sense

view the insect moves towards the candle, because it likes the

light. There is one and only one fairly evident inference from the

teleological way of looking at the matter. It implies that the moth

should always fly from the darker to the brighter situation. Now the

interpretation of its movement in terms of reflex action signifies that

it is the direction of the light rays and not primarily the intensity

of illumination which determines the direction of its movement. In

Nature moving along the direction of the rays towards the source of

light usually involves progression from a darker to a brighter region.

In the laboratory it is easy to arrange conditions so that an insect

crawling along the direction of an obliquely incident beam, moves from

a brighter to a darker area, as it approaches the source. In doing so

it behaves, as it would be predicted to behave in such a situation

on the assumption that its behaviour is determined by reflex action.

According to the teleological view it should do the opposite.

Even in the behaviour of so capricious an animal as man himself, it

is possible to isolate units of behaviour to which the term _reflex_

is appropriate. The entire behaviour of a pithed frog or of a dog

deprived of its brain can be regarded as the summation of a number

of discrete reflexes compounded according to ascertainable laws. The

problem is not a simple one; but the way in which the operation of

one reflex affects the exercise of another has been elucidated with

considerable success by Sherrington and his co-workers. Sherrington has

paid special attention to what occurs in the simultaneous application

of two stimuli whose appropriate responses involve the propagation

of impulses along common fibres within the central nervous system.

A further complication is introduced by the existence of inhibitory

reflexes, responses which involve the cessation or the diminution of

activity already in progress before the application of the stimulus.

The work of Magnus and his colleagues, who have solved the riddle of

how a cat falls on all fours, demonstrates to a very large extent the

possibility of interpreting balancing movements of the body as the

summation of such reflexes as are readily exhibited in the brainless

or “spinal” animal. Yet few physiologists have ventured to entertain

the likelihood that the entire behaviour of even such an animal as a

cat, still less man himself, could be treated successfully in this

way. Hence has arisen the traditional distinction between reflex and

voluntary activity. So long as that distinction was a valid one,

biology admitted a fundamental dualism in its subject matter and in its

method. The vitalist was in a position to claim that there is a group

of properties of living matter in dealing with which we must adopt

introspective rather than physical methods of enquiry. The mechanist

might reply epigrammatically that physiology deals with what we know

about the central nervous system, psychology with what we do not know.

The distinction still remained.

There are certain fairly evident reasons why the behaviour of a frog

deprived of its brain should be simpler than that of the intact animal.

One is that the number of possible paths along which nervous impulses

can pass is much smaller. Another is the fact that the brain receives

the nerves which bring in impulses from the three great receptor

organs, or, in the older terminology, sense organs of the head. The eye

and the ear bring the organism within the range of physical influence

of innumerable events remotely situated in space. When we have allowed

for all such differences there remains a perfectly tangible distinction

between the behaviour of the spinal and that of the intact animal.

The response that we have hitherto called a reflex is such that for a

given agency under the same external conditions we may expect the same

result. There are the best of reasons, based not on any introspective

ideas but upon the study of behaviour to make us think that however

much we standardize the external conditions at the moment, when the

stimulus is applied, we can never predict from that alone exactly

what will happen as the result of the application of certain types of

stimuli. The performance of “learning” justifies this conclusion, and

it has been customary in the past to refer this property of living

matter to essentially non-physical concepts such as _memory_. By

defining in this way the distinction between reflex behaviour in the

traditional sense and voluntary or conscious behaviour, a new problem

has emerged. This may be stated in the following way. If instead of

concentrating exclusively on what is happening at the moment, we take

into consideration the way in which a given stimulus has been presented

to an organism on previous occasions, is it possible to establish any

relation between the effect it now produces and the events associated

with its application antecedently? In so stating the issue we have

introduced no new and introspective concepts foreign to the traditional

physiology of the reflex. We have simply envisaged the possibility of

studying conditions under which new reflex systems may be brought into

being.

§2

It is this problem which the Russian physiologist Pavlov and his

co-workers have attacked with such conspicuous success during the

past two decades. For some time their researches remained little known

in this country, but two translations of Pavlov’s lectures are now

accessible to the English-speaking reader. There is therefore no need

to go into details concerning the experimental technique which is

formidable. The more significant developments of the subject may be

dealt with by considering how aspects of behaviour which were formerly

referred to the introspective concepts of memory, attention and

sensation can now be investigated without departing from the language

adopted by physiologists, when describing the properties of simple

reflex action.

Pavlov’s investigations commenced with the study of salivary secretion

in dogs. A dog which has been deprived of the forebrain secretes

saliva, when food is introduced into the mouth. The intact animal also

secretes saliva, when food is brought within the range of its eyes or

nostrils. In the adult the sight or smell of food is an appropriate

stimulus for reflex salivary secretion. The ringing of a bell is

ordinarily without effect on the secretion of saliva; but the ringing

of a bell if repeated a certain number of times, when food is also

presented, eventually comes to evoke salivary secretion, when food

does not accompany it. In general it is found that, in the intact

animal, a previously indifferent stimulus applied at suitable intervals

simultaneously with the application of a stimulus which unconditionally

evokes a reflex response is found to acquire the property of evoking

the same reflex response, when unaccompanied by the original or

“unconditioned” stimulus. A new reflex has been built up. Such reflexes

are called by Pavlov _conditioned_ reflexes, and the previously

indifferent stimulus is called the conditioned stimulus. Any event in

the external world which affects a receptor organ may in the intact

animal become a conditioned stimulus, provided external conditions

are rigidly standardized in other respects, provided also that it

accompanies the unconditioned stimulus a sufficient number of times

depending on whether the application is precisely simultaneous, whether

the conditioned stimulus begins to operate before the unconditioned,

overlapping it in duration or separated from it by a short interval.

The task of defining the facility with which a conditioned reflex is

built up involves a study of the significance of the interval between

successive applications of both stimuli and of the juxtaposition of

conditioned and unconditioned stimulus. In defining the conditions

which determine the bringing into being of a new reflex system by this

method, we are investigating a class of phenomena which would formerly

have been attributed to “memory.” At no point is it necessary to depart

from the conventions of scientific nomenclature; and in place of a

descriptive epithet, we arrive at a definite specification regarding

when and whether an event will occur.

What it has been the custom to denote by the term memory is only one

aspect of the problem of “conscious” or “voluntary” behaviour, that

is to say those aspects of behaviour which are spatially referable to

reflex paths in the fore brain. An animal is constantly subject to

the simultaneous application of many indifferent and unconditioned

stimuli, but its behaviour is selective. This introduces the problem

of _attention_. To ascertain the conditions which prevent new reflex

systems from coming into being, or extinguish them when they have

become established, was perhaps the most important aspect of Pavlov’s

work, because an understanding of this part of the problem underlies

the successful control of experimental procedure. The possibility of

isolating a conditioned reflex for study implies the existence of

some inhibitory agencies which prevent the normal surroundings of the

laboratory from exerting a significant influence on the course of

the experiment. The inhibition of conditioned reflexes is a complex

question; and its complexity emphasizes how broad a basis they offer

for the interpretation of “conscious” behaviour in general and the

interpretation of _attention_ in particular.

From this standpoint two important types of inhibition are called

by Pavlov inhibition by extinction and conditional inhibition. The

first term refers to the fact that, when an indifferent stimulus has

been converted into a conditioned stimulus, and is then allowed to

act repeatedly without the unconditioned stimulus, it gradually loses

its potency, regaining it after an interval of rest. Conditional

inhibition is the extinction which occurs, when a new indifferent

stimulus is superimposed upon the effective phase of a conditioned

stimulus. A third and especially important form of inhibition is the

extinction of a state of inhibition by conditional inhibition, or as

Pavlov calls it, inhibition of inhibition. Let us suppose that an

organ note of one thousand vibrations per second has been made the

signal for salivary secretion by repeated application of the stimulus,

when food is administered to the animal. If it is now administered

repeatedly without the accompaniment of food, it suffers inhibition

by extinction, but recovers its efficacy after a period of rest. If,

during the indifferent period, the experimenter superimposes on the

now ineffective sound stimulus another indifferent agent such as the

flash of a lamp before the dog’s eyes, secretion of saliva ensues.

The sound regains its efficacy as a conditioned stimulus. One other

type of inhibition which can be studied experimentally is “generalized

inhibition” or elimination of the activity of the fore brain, which can

be brought about in the dog by local warming or cooling of an area of

the skin. This has an intimate bearing on the phenomena of sleep and

hypnotic trance, as also on the advantages of summer time.

Perhaps the most radical consequence of the line of work which we

are now considering lies in the possibilities which it presents for

inverting our traditional attitude to the discussion of “sensation.”

When we can isolate some simple unconditioned response to a particular

stimulus, we can investigate the extent to which the efficacy of

the stimulus is localized with reference to some receptive area,

and discuss the sense organ in the same way as a piece of physical

apparatus. We know for instance that a frog does not respond to white

or black background by the appropriate change in colour of the skin, if

its eyes are removed. The influence of the earth’s gravitational field

on the way in which a frog maintains its normal balance in swimming

provides another illustration of the way in which the experimental

biologist deals with the phenomenon of receptivity, when it is possible

to isolate a type of response which invariably accompanies a particular

type of stimulation. In this instance the receptor is that part of the

internal ear known as the labyrinthine organ. After destruction of the

labyrinthine organ on one side only, a frog swims in a spiral path. If

the internal ear of both sides is removed, it swims hither and thither,

as likely as not upside down or sideways without any sign of its normal

maintenance of balance. The inner ear of the frog or man with its

three semicircular canals in the three Cartesian planes is a rather

elaborate example of a type of receptor organ represented in shrimps

by two little sacs called statocysts at the base of the feelers.

These sacs contain concretions of sand known as the statoliths.

Experimentally the sand can be replaced by iron filings. If this is

done, the shrimp swims upside down, when a strong electromagnet is

placed above it. The position occupied by the statolith in its sac is

determined by the pull of gravity in ordinary circumstances. When the

body is bent, the statocyst comes into contact with a new portion of

the wall of the sac, thus stimulating a different set of nerve fibres,

and initiating appropriate muscular reflexes. The balancing movements

of a shrimp in swimming also depend on the eyes. With both feelers

removed a shrimp swims normally in daylight. It loses its balance

completely in a dark room; and swims on its back if illuminated from

below. Removal of one eye or one statocyst does not affect its balance

in daylight, unless the two operations are performed on the same

animal. It then swims in spirals.

A modern biologist adopts to the statocyst and the eye the same

attitude which he would adopt to the self starter of a motor car, if he

were quite ignorant of its mechanism. Sometimes his problem is further

complicated by the necessity of turning on the switch before the engine

will start, adjusting the spark or cutting down the air. In an animal

whose behaviour is largely conditioned behaviour, it is not so easy to

isolate simple invariable responses to particular types of external

agency. We lapse into the language of introspective psychology. Pavlov

has shown that this is unnecessary. By employing the method of building

up conditioned reflexes to define the limits of discrimination, the

analysis of sensation can be carried out without departing from the

attitude which we adopt to a motor car. Let us suppose that the sound

of a tuning fork of 256 vibrations per second, i.e. middle C, is

accompanied by electrical stimulation of the paw of the dog, until the

note itself becomes an effective stimulus for withdrawal of the paw.

A tuning fork of 264 vibrations will also evoke the withdrawal of the

paw; but the application of the second stimulus suffers inhibition by

extinction before the original (middle C), as can be shown by applying

the latter after response to the tuning fork of 264 vibrations has

been extinguished. Applying series of tuning forks in such experiments

it is found that the limits of discrimination in dogs is a fraction

of a tone. The delicacy of this method of testing discrimination or

selective receptivity to a given range of stimuli depends on the fact

that it is possible not merely to show whether one stimulus can be

substituted for another in a conditioned reflex but to measure the

extent to which a given stimulus can replace another. Judged from this

standpoint dogs and cats are colour blind, as far as such a statement

can have any tangible meaning. That is to say, differences of light

intensity but not of wave length in the effective range determine the

reactions of these animals to photic stimuli.

§3

In the light of Pavlov’s work the problem of conscious behaviour, or

as we should now say conditioned behaviour, no longer presents itself

to biological enquiry as a domain in which the methods of traditional

physiology must be abandoned in favour of introspective speculation.

It becomes the problem of defining how new reflex systems can be

built up. The possibility of a further analysis of the process on

mechanistic lines will be discussed elsewhere. Whatever success attends

such an attempt, the fact remains that the controversy between the

mechanistic and vitalistic schools must now be conducted on a new

basis. Mechanistic biology could not claim to take a comprehensive view

of the properties of living matter, so long as it failed to indicate

how “voluntary” activity, as it was almost universally denoted by

physiologists, differs from reflex activity. It is true that some of

the more radical mechanists like Loeb preferred to speak of associative

behaviour as having a more objective flavour. But Loeb’s own use of the

concept of “brain images” emphasizes how fundamental is the innovation

which the work of Pavlov’s school has introduced into philosophical

discussion. The mechanist never legitimately claimed more than the

right to investigate the properties of living matter in its simpler

manifestations by those methods whose success had been justified in

the domain of physics and chemistry. If the mechanist ventured to

speculate beyond those limits he transgressed his terms of reference.

Until the publication of the work of Pavlov’s school physiology was

tied hand and foot to the traditional distinction between reflex and

voluntary behaviour. Thus the author of a standard work on human

physiology with a distinctly mechanistic tendency writes on the

functions of the cerebellum: “... the degree of consciousness, if any,

exhibited by the cerebellum is of a much lower order than that shown

by the cerebrum. All observers agree that there is no apparent loss of

sensation after removal of the cerebellum, but Luciani, Russell and

others state their belief that in some indefinable way it is affected

by such operations. Whatever functions of this kind are present we can

define only by the unsatisfactory terms of subconscious rather than

unconscious...” What Howell wrote in 1905 might have been written by

any mechanist of that period. The physiologist inevitably lapsed into

introspective terminology, when dealing with brain physiology; and it

is this restricted mechanistic outlook which Dr. Haldane has attacked

in his recent Gifford Lectures. It is not difficult to show that the

mechanist, as that term is used by Dr. Haldane, accepted implicitly the

Cartesian compromise. It is surprising that, although Pavlov’s work

has been generally accepted by contemporary biologists, Dr. Haldane

completely refrains from considering its bearing on the present status

of the mechanistic conception of life.

Dr. Haldane’s statement that the method of traditional, i.e.

mechanistic, physiology “tells us nothing, however far we may extend

it, regarding the distinctive characters of conscious behaviour” is

especially remarkable. Although few writers have hitherto ventured to

formulate the far-reaching philosophical consequences of Pavlov’s work,

more than fifteen years have passed since the veteran physiologist Sir

William Bayliss made the following pronouncement:

“Pavlov states that he was struck by the fact that when the

physiologist leaves the study of the simpler parts of the central

nervous system which he has investigated by the observation of

reflexes, and proceeds to the higher parts, his methods suddenly

change. He gives up the observation of the relation between

external phenomena and the reaction of the organism to them and

introduces psychological ideas, derived from his own internal

consciousness. To extend to the higher centres the method of

observing what changes in the organism are correlated with external

changes might appear too difficult, but Pavlov has succeeded in

doing so to a remarkable degree” (_General Principles_, 1914, p.

502).

In denouncing the mechanistic view of life as set forth by Professor

Donnan at the meeting of the British Association in 1928, Dr. Haldane

states:

“I regard this view as now entirely obsolete, since it ignores

the facts, and this is far more evident now than it was a few

years ago, before physiology had become to so large an extent a

_quantitative science_” (italics inserted) “... The fact that

Professor Donnan, though his work in physical chemistry commands

universal respect among those who know it, is not a physiologist,

may partly account for his opinions.”

Perhaps also the fact that Dr. Haldane, whose work on the physiology

of respiration and excretion commands universal respect among those

who know it, neglects in his Gifford Lectures to make any reference to

the work of Pavlov may partly account for his belief that “a biologist

interprets his observations in a different manner from a physicist”

(p. 97). It is certainly permissible to state that Dr. Haldane is not

speaking for biologists as a whole, when he denies that the problem

of conscious behaviour can ever be attacked successfully by the

traditional method of the physiologist.

Biologists may be expected to differ in the hopes they may entertain

as to the progress of further investigation. We can at least envisage

the possibility that biology will advance towards a comprehensive

account of the properties of living matter without interpreting its

observations in a manner different from that adopted in physics. The

work of Pavlov’s school shows that it is not necessary to introduce

concepts foreign to other parts of biology in dealing with conscious

behaviour. Of late years the notion of matter which is so fundamental

to common sense has been disintegrated by the advance of the physical

sciences. The notion of mind or consciousness so fundamental to common

sense is being disintegrated by contemporary biology in an analogous

way. If materialism in the traditional sense is dead, idealism in

its traditional form is dead. Like traditional dualism they are dead

because they never contained within themselves the capacity for

growth. The success of biology in attacking the problem of “conscious

behaviour” in Haldane’s terminology has been consistent with the

attitude of treating _conditioned behaviour_ as an aspect of the

properties of a peculiar kind of matter, living matter. In that sense

the new philosophical outlook which emerges from Pavlov’s work is a

materialistic one.

Physiology has at length discovered a neutral ground for the

investigation of the problem of learning. If it is too early to

predict the final outcome of this advance, it is permissible to

proffer some tentative suggestions concerning its influence on the

future of philosophical discussion. From Plato to modern times

philosophical enquiry has mainly occupied itself with what Kant calls

“the problems of mere pure reason.” Of these Kant enumerates God,

Freedom and Immortality as the three principal objects of philosophical

enquiry. For the final solution of these problems, Kant asserted that

“philosophy stands in need of a science which shall determine the

possibility, principles and extent of human knowledge _a priori_.”

Introspective psychology was the “science” to which he assigned this

task. Introspective psychology has failed to fulfil the expectations

which Kant entertained, when he concluded the _Critique_ by expressing

the hope that it “would bring reason to perfect contentment in

regard to that which has always, but without permanent results,

occupied her powers and engaged her ardent desire for knowledge.”

The type of psychology which Kant promoted had already begun to

sever its connexion with moral philosophy before the emergence of

the Behaviourist tendency in an explicit form. Kant did not refute

Hume’s arguments when he proposed the question, “whence could our

experience acquire certainty, if all the rules on which it depends were

themselves empirical and fortuitous”? He stated a problem. For its

solution he lacked a method. For its discussion he lacked a vocabulary.

If the physiology of human learning continues to progress under the

Behaviourist influence to which Pavlov’s work has given birth, Kant’s

solution of the problem, which he himself propounded, must eventually

be relegated to the same status as astrology and palmistry in the

history of human knowledge.

The strength of Kant’s case against Hume’s empiricism lay in the

immature state of physiological knowledge, when the _Critique of

Pure Reason_ was published. Kant’s views on Space and Time were

circumscribed by the biological limitations of his period. The Kantian

conception of experience was defined by the influence of light, sound,

chemical stimuli, mechanical pressure and temperature affecting the

eye, the ear, the nose, the mouth and the skin--the only receptor

organs recognized by the physiologists of the eighteenth century. Two

of the most important instruments of receptivity in the human body, the

labyrinthine organ and the proprioceptors which respond to the state

of tone of the muscles, were not studied till the nineteenth century.

If Kant had been familiar with the physiology of the labyrinthine

organ, he would not have argued with the same cogency that the concept

of space is essentially different from the concept of weight. The

_a priori_ necessity of the proposition that “space has only three

dimensions” was determined, according to Kant, by the existence of an

“external sense” which is “a property of the mind.” If he had lived

fifty years later he would have realized that the “necessity” of the

Cartesian frame work is a material consequence of the structure of the

internal ear. If Kant had been familiar with Sherrington’s work on

the proprioceptor organs, he would have seen a deeper significance in

the experiment which Galileo performed, when he used his own pulse to

measure the period of a swinging lamp. Kant was compelled to attribute

the “_a priori_ necessity” of the proposition that “time has only

one dimension” to “the internal sense by which the mind contemplates

itself.” The time conditioned reflexes which Pavlov has demonstrated

are intelligible to modern physiology without recourse to a “faculty

of pure _a priori_ cognition.” The human body is itself a clock from

whose tickings we can never escape. Periodic changes in tone of the

body muscles influence the proprioceptor organs in a manner essentially

analogous to the way in which light exerts its effect on the eye.[2]

Kant’s physiology calls for more detailed treatment elsewhere. In

concluding this essay, I must remove one source of misunderstanding. I

do not assert that all aspects of conscious behaviour will eventually

be explained in terms of Pavlov’s conditioned reflexes. I do affirm

that Pavlov has successfully applied the methods of traditional

physiology to the study of processes presumably included in Dr.

Haldane’s definition of conscious behaviour. The strength of Dr.

Haldane’s position lies in the fact that behaviour ceases to be called

conscious so soon as it is possible to bring it within the range of

scientific prediction. I can well believe that the vitalists of fifty

years hence will be assuring their opponents that they never regarded

the process of learning, the phenomenon of attention or sensory

discrimination as characteristics of the conscious state.

II. THE ATOMISTIC VIEW OF PARENTHOOD

“When you can measure what you are talking about, and express

it in numbers, you know something about it; but when you cannot

measure it, when you cannot express it in numbers, your knowledge

is of a meagre and unsatisfactory kind; it may be the beginning

of knowledge, but you have scarcely in your thoughts advanced to

the stage of science whatever the matter may be...”--Lord Kelvin,

_Addresses_

§1

The future progress of biological science depends upon a large number

of unpredictable contingencies, some political, others meteorological.

The collision of the earth with a comet may leave the fate of the

argument between the mechanist and the vitalist for ever unsettled.

There is therefore no justification for a dogmatic assertion that

all the properties of living matter will eventually be reduced to

the same hypotheses as are adopted in physical chemistry. But it is

doubtful whether any biologists of the mechanistic persuasion have on

any occasion explicitly committed themselves to so rash a statement.

The vitalistic Sarah Gamp has invented a mechanistic Mrs. Harris with

the express object of giving her a piece of her mind. As a polemical

device this is most valuable, especially in political propaganda. It

does not help the mechanist to understand what vitalism can offer as a

guide to further biological enquiry. His perplexity is increased by the

circumstance that so many vitalists of the platform behave themselves

with mechanistic propriety in the laboratory. Dogmatism is at least as

frequent among those who call themselves vitalists as among mechanists.

The vitalist does not qualify his denial that a complete solution

of the riddle of life can be obtained in physico-chemical terms. The

mechanist is usually content to state that he knows of no other terms

in which an intelligible solution could be found. The vitalist even

goes further, and, quite inconsistently with his laboratory practice,

if he is a competent biologist, asserts, that in its very methodology,

biology is an _independent_ science. A biologist, says Dr. Haldane

in his Gifford Lectures, “interprets his observations in a different

manner from that of the physicist.”

This I think is the main bone of contention between the two attitudes

which are generically denoted by the terms mechanistic and vitalistic.

The real issue has shifted from deciding whether the hypotheses

of physics and chemistry suffice for the interpretation of vital

phenomena to deciding whether there is an essential difference between

the logical structure of those branches of science that deal with

living matter and those which deal with inanimate objects. This is a

welcome change, because it presents a much more genuine and concrete

problem for solution. It is somewhat surprising that the controversy

should undergo such a metamorphosis at the present moment. The recent

development of evolutionary biology is especially calculated to

reinforce the belief that biological theory only progresses, when the

biologist adopts towards the subject matter of his investigations the

same attitude as that which the chemist and physicist adopt towards the

objects which they study. In our generation it is possible to find in

those aspects of biology which are most recalcitrant to the application

of physico-chemical hypotheses the most conspicuous examples of a

fundamental similarity in the logical procedure which the biologist

on the one hand and the physicist or chemist on the other employ in

constructing their hypotheses. It would not be possible to select from

the whole field of biological science a more striking illustration of

the success of quantitative and experimental methods than the recent

extension of Mendel’s hypothesis by Morgan’s school. This advance

has entailed an extensive elimination of teleological concepts in

the interpretation of the evolutionary process. Yet the phenomena of

heredity and variation at present lie completely outside the scope of

physico-chemical analysis in the ordinary sense of the term; and any

attempt to formulate the problems of genetics in physico-chemical terms

is still a matter of pure conjecture.

In this sense we may agree with one writer of the vitalistic school in

saying that to speak of the “mechanism of heredity” is a meaningless

collocation of words. But if our interest is primarily directed not

to the end product itself but towards the way in which the scientist

proceeds to elaborate his hypotheses, the study of heredity provides

a particularly clear example of how a hypothesis developed without

any departure from the _principle of mechanism_ can yield verifiable

conclusions about the behaviour of living systems. From this point of

view it is both legitimate and intelligible to speak of the mechanisms

of heredity and variation; and the expression is as permissible as the

analogous phrase, the mechanism of chemical reaction. A comparison

of the growth of the Mendelian principle with Dalton’s atomic theory

of the structure of matter will help us to see whether the biologist

does actually interpret his observations in a manner different from

that adopted by the student of non-living matter, and whether the

biologist has recourse to a kind of logic which is different from

the logic which the physicist and chemist employ in framing their own

generalizations.

When Mendel took up the problem of hybridization, the nature of

fertilization in plants was known in a general way. Just a century

before Mendel began his work Kolreuter by painting pollen from one

individual on to the stigmas of another variety, and vice versa, had

shown that hybrids inherit equally from the pollen and seed plant. At

the end of the eighteenth century and the beginning of the nineteenth,

Knight and Goss in England had made further progress in crossing pure

bred varieties by calling attention to the “splitting” of hybrids, or

reappearance of parental types when intercrossing hybrid offspring.

Contemporaneously with Mendel, Naudin in France studied this phenomenon

more closely, and came very near to formulating Mendel’s principle.

His results were published in 1862. These pioneers in hybridization

laid down the necessity of working with what to the geneticist is like

pure chemicals to the chemist, pure breeding stock. They fell short of

arriving at far-reaching results, because their attitude to heredity

was dominated by the holistic standpoint. They could only think of

the plant in terms of a preconceived notion of individuality. They

refrained from focusing their attention on the separate parts, and

following out the fate of discrete characteristics in their crosses.

We must not overlook the debt which Mendel owed to the pioneers of

hybridization. There would have been no modern chemistry if the

Arabs and alchemists had not devoted years of laborious study to the

clarification of our idea of a pure substance; and there would have

been no genetics, if the idea of pure breeding stock had not been laid

down by Mendel’s predecessors. Chemistry failed to progress beyond

the stage of describing new compounds so long as it remained entangled

in the vitalistic “phlogiston” concept; and genetics, the study of

heredity and variation, remained purely descriptive, until it was

emancipated by Mendel from the holistic tendency to concentrate upon

the organism as a whole. Naudin did in fact envisage less definitely

than Mendel the atomistic concept of heredity, just as William Higgins

had partly visualized the chemical possibilities of atoms before Dalton

published his theory.

Mendel used in his researches pure breeding stocks differing only in

well-defined particulars, employing single characteristics as units

of study, and recording the progeny of every cross separately for

comparative observation. In his original work Mendel chiefly dealt

with the common pea, which possesses two advantages which recommend

it for such experimentation, namely, that its flowers are capable

of self fertilization (i.e., the pistil can be pollinated from the

stamens of the same flower) and that it has a number of well-marked

varieties distinguished by tangible characteristics such as the shape

(round or wrinkled) and colour (green or yellow) of the seeds, or the

stature (tall or dwarf) of the shoot, etc. In all his crosses involving

a single difference of this kind he found that the first generation

of the cross resembled one of the parents. When these crossbreeds

were self fertilized, they produced offspring resembling the original

parents in the constant ratio of three to one. One-quarter of the

offspring of the crossbreeds resembled one parent and bred true;

one-quarter resembled the other parent and bred true; and the remaining

half being like the “dominant” parent, which the first generation

of hybrids resembled, behaved exactly like the latter, when self

fertilized.

An investigator who had not the attitude which makes a capable chemist

might have been distracted by the peculiar circumstance of dominance,

or the resemblance of the impure individuals to one of the parents

exclusively. Mendel rightly judged this to be insignificant. A chemical

analogy will perhaps assist to make this clear. Sodium and potassium

yield colourless salts with most common acids, but the permanganates

of both are purple in solution. The salts of copper are generally of

a bluish or greenish tint in solution. In the one case the anion, in

the other case the kation, is the dominant factor in determining the

physical property of colour; but in both cases the other component

behaves in any reaction with no less characteristic efficacy, because

its presence is seemingly masked. So likewise Mendel looked beyond the

bodily resemblance of the dominant parental and hybrid individuals

to their hereditary makeup; and recognized in his experimental data

two general conclusions which prompted special consideration. One

was the fact that the original parental types can be recovered in

all their purity. The other was the fact that the various hereditary

types produced by hybridization regularly appear in the same numerical

ratios. Both conclusions are of universal validity, though Mendel had

the very good fortune to select materials which yield the simplest

type of numerical results which occur in crosses between pure strains.

When Dalton formulated the atomic hypothesis two fundamental empirical

generalisations of chemistry were fully accredited. The law of the

conservation of matter and the law of constant proportions had been

established. Mendel found in his data the proof of what we might call

the principle of the conservation of genetic materials and the law of

constant genetic proportions. To the recognition of these empirical

generalizations he added a conceptualization of the basis of their

existence in terms of discrete factors. These factors were according

to Mendel’s hypothesis (or Mendel’s “first law”) units of hereditary

combination, just as Dalton’s atoms were units of chemical combination.

Each character involved in his crosses was regarded by Mendel as

determined by a factor derived from the maternal and one derived from

the paternal parent. A pure individual was thus represented by _aa_

or _bb_, and an impure individual by _ab_. Mendel assumed that _a_

and _b_ are atoms of heredity in the sense that they retain their

separate entities through the whole course of development. Having

introduced this conception, he showed that all his numerical data

followed from the laws of chance, if the maternal and paternal factors

which determine a particular character separate in the formation

of the gametes (pollen and ovules) so that one-half of the gametes

contain only the maternal and one-half only the paternal factor for the

character considered. The combinations which may occur as the result of

fertilization are compatible with the assumption that any given male

gamete (pollen or sperm) may fertilize any given female gamete (ovule

or egg cell). Mendel’s first law may then be stated thus: characters

distinguishing different hereditary strains depend upon factors which

are inherited from both parents and _segregate_ in the formation of

the gametes, so that one-half contain the paternal and one-half the

maternal factor. Mendel tested the implications of this hypothesis by

crossing his hybrids to pure types with verifiable results. He then

proceeded to make crosses involving two or three character differences.

This led him to enunciate a second law which might be compared with the

law of multiple proportions in chemistry, for its validity is of less

general significance than the first law. It served eventually to direct

attention to the much more complicated numerical results which arise in

dealing with character differences attributable not to one but several

pairs of factors. The analysis of such cases was left to Mendel’s

successors.

There is internal evidence in Mendel’s writings to support the

view that Mendel himself realized that the atomistic conception of

inheritance would demand a drastic revision of the prevailing notion

of variation. To Mendel’s generation, to Darwin and the pioneers of

Natural Selection, variation and heredity were co-extensive terms.

Offspring were always on the whole like their parents, but always on

the other hand a little different. So the species in conformity with

sound liberal principles broadened down from precedent to precedent.

But on the atomistic view heredity is essentially conservative, and

variation essentially revolutionary. For an indefinite number of

generations the atoms of heredity remain unchanged. But times come,

when the political barometer falls, and the change when it happens is

a discontinuous one. Something new has been brought into being, as

when lead is produced from the disintegration of radium or another

allotropic modification of an element is formed. The full implications

of this were not destined to be realized till forty years had elapsed.

Meanwhile the evolutionary ship drifted upon an uncharted ocean of

speculation without the compass of experiment to direct its course.

§2