In 1860 Spencer commenced a connected series of philosophical
works, designed to unfold in their natural order the principles of
biology, psychology, sociology and morality. "Principles of
Biology" was published in 1864, and aims to set forth, the general
truths of biology as illustrative of, and as interpreted by the
laws of evolution. It was revised in 1899.
_Proximate Definition of Life_
To those who accept the general doctrine of evolution, it needs scarcely
to be pointed out that classifications are subjective conceptions which
have no absolute demarcations in nature corresponding to them.
Consequently in attempting to define anything complex we can scarcely
ever avoid including more than was intended, or leaving out something
that should be taken in. Thus it happens that on seeking a definition of
life there is great difficulty in finding one that is neither more nor
less than sufficient. As the best mode of determining the general
characteristics of vitality, let us compare its two most unlike kinds
and see in what they agree.
Choosing _assimilation_, then, for our example of bodily life, and
_reasoning_ for our example of the life known as intelligence, it is
first to be observed that they are both processes of change. Without
change food cannot be taken into the blood nor transformed into tissue:
neither can conclusions be obtained from premises. This conspicuous
manifestation of change forms the substratum of our idea of life in
general. Comparison shows this change to differ from non-vital changes
in being made up of _successive_ changes. The food must undergo
mastication, digestion, etc., while an argument necessitates a long
chain of states of consciousness, each implying a change of the
preceding state. Vital change is further made up of many _simultaneous_
changes. Assimilation and argument both include many actions going on
together. Vital changes, both visceral and cerebral, also differ from
other changes in their _heterogeneity_; neither the simultaneous nor the
serial acts of digestion or of ratiocination are at all alike. They are
again distinguished by the combination subsisting among their
constituent changes. The acts that make up digestion are mutually
dependent; as are those which compose a train of reasoning. Once more,
they differ in being characterised by definiteness. Assimilation,
respiration, and circulation, are definitely interdependent. These
characterisations not only mark off the vital from the non-vital, but
also creatures of high vitality from those of low vitality. Hence our
formula reads thus:--_Life is the definite combination of heterogeneous
changes, both simultaneous and successive._ Not _a_ definite
combination, allowing that there may be others, but _the_ definite
combination. This, however, omits its most distinctive peculiarity.
_Correspondence Between Life and Its Circumstances_
We habitually distinguish between a live object and a dead one by
observing whether a change in the surrounding conditions is or is not
followed by some perceptible and appropriate change in the object.
Adding this all-important characteristic, our conception of life
becomes--the definite combination of heterogeneous changes, both
simultaneous and successive, _in correspondence with external
coexistences and sequences_. Some illustrations may serve to show the
significance of this addition.
Every act of locomotion implies the expenditure of certain internal
mechanical forces, adapted in amounts and directions to balance or
outbalance certain external ones. The recognition of an object is
impossible without a harmony between the changes constituting perception
and particular properties coexisting in the environment. Escape from
enemies supposes motions within the organism related in kind and
rapidity to motions without it. Destruction of prey requires a
particular combination of subjective actions, fitted in degree and
succession to overcome a group of objective ones.
The difference of this correspondence in inanimate and animate bodies
may be expressed by symbols. Let A be a change in the environment; and B
some resulting change in an inorganic mass. Then A having produced B,
the action ceases. But take a sufficiently organised living body, and
let the change A impress on it some change C; then, while the
environment A is occasioning _a_, in the living body, C will be
occasioning _c_: of which _a_ and _c_ will show a certain concord in
time, place, or intensity. And while it is in the continuous production
of such concords or correspondences that life consists, it is _by_ the
continuous production of them that life is maintained.
As, in all cases, we may consider the external phenomena as simply in
relation, and the internal phenomena also as simply in relation, the
broadest and most complete definition of life will be:--_the continuous
adjustment of internal relations to external relations_. It will be
best, however, commonly to employ its more concrete equivalent--to
consider the internal relations as "definite combinations of
simultaneous and successive changes"; the external relations as
"coexistences and sequences," and the connection between them as a
"correspondence."
_The Degree of Life Varies as the Degree of Correspondence_
It is now to be remarked that the life is high in proportion as this
correspondence between internal and external relations is
well-fulfilled.
Each step upward must consist in adding to the previously adjusted
relations which the organism exhibits some further relation, parallel to
a further relation in the environment. And the greater correspondence
thus established must, other things being equal, show itself both in
greater complexity of life and greater length of life--a truth which
will be duly realised on remembering the enormous mortality which
prevails among lowly-organized creatures, and the gradual increase of
longevity and diminution of fertility which is met with in ascending to
creatures of higher and higher development. Those relations in the
environment to which relations in the organism must correspond increase
in number and intensity as the life assumes a higher form. Perfect
correspondence would be perfect life.
_Growth, or Increase of Bulk_
Perhaps the widest and most familiar induction of biology is that
organisms grow. Under appropriate conditions increase of size takes
place in inorganic aggregates as well as in organic aggregates. Crystals
grow. Growth is indeed a concomitant of evolution. The several
conditions by which the phenomena of organic growth are governed,
conspiring and conflicting in endless ways and degrees, qualify more or
less differently each others' effects. Hence the following
generalisations must be taken as true on the average, or other things
equal:--
First, that growth being an integration with the organism of such
environing matters as are of like nature with the matters composing the
organism, its growth is dependent on the available supply of such
matters. Second, that the available supply of assimilable matters being
the same, and other conditions not dissimilar, the degree of growth
varies according to the surplus of nutrition over expenditure. Third,
that in the same organism the surplus of nutrition over expenditure is a
variable quantity; and that growth is unlimited or has a definite limit
according as the surplus does or does not progressively decrease,--a
proposition exemplified by the increasing growth of organisms that do
not expend force, and by the definitely limited growth of organisms that
expend much force. Fourth, that among organisms that are large expenders
of force, the size ultimately attained is, other things equal,
determined by the initial size. Fifth, that where the likeness of other
circumstances permits a comparison, the possible degree of growth
depends upon the degree of organisation: an inference testified to by
the larger forms among the various divisions and subdivisions of
organisms.
_Why Do Organisms Cease to Grow_
Why should not all organisms, when supplied with sufficient material,
continue to grow as long as they live? We have found that organisms are
mostly built up of compounds which are stores of force. These substances
being at once the materials for organic growth and the sources of
organic force, it follows, from the persistence of force, that growth is
substantially equivalent to the absorbed nutriment minus the nutriment
used up in action. This, however, does not account for the fact that in
every domestic animal the increments of growth bear continually
decreasing ratios to the mass, and finally come to an end. Nevertheless,
it is demonstrable that the excess of absorbed over expended nutriment
must decrease as the size increases. Since in similar bodies the areas
vary as the squares of the dimensions and the masses vary as the cubes,
it follows that, however great the excess of assimilation over waste may
be during the early life of an active organism, there must be reached,
if the organism lives long enough, a point at which the surplus
assimilation is brought to nothing--a point at which expenditure
balances nutrition, a state of moving equilibrium. Obviously, this
antagonism between assimilation and expenditure must be a leading cause
of the contrast in size between allied organisms that are in many
respects similarly conditioned.
_Development, or Increase of Structure_
In each of the organic sub-kingdoms the change from an incoherent,
indefinite homogeneity to a coherent definite heterogeneity is
illustrated in a quadruple way. The originally-like units or cells
become unlike, in various ways, and in ways more numerously marked as
the development goes on. The several tissues which these several classes
or cells form by aggregation, grow little by little distinct from each
other; and little by little become structurally complex. In the shoot as
in the limb, the external form, originally very simple and having much
in common with countless simple forms, organic and inorganic, gradually
acquires an increasing complexity, and an increasing unlikeness to other
forms, and meanwhile, the remaining parts of the organism, having been
developed severally, assuming structures diverging from each other and
from that of this particular shoot or limb, there has arisen a greater
heterogeneity in the organism as a whole.
The most remarkable induction of von Baer comes next in order. It is
that in its earliest stage every organism has the greatest number of
characters in common with all other organisms in their earliest stages;
that at each subsequent stage traits are acquired which successively
distinguish the developing embryo from groups of embryos that it
previously resembled--thus step by step diminishing the group of embryos
which it still resembles; and that thus the class of similar forms is
finally narrowed to the species of which it is a member. For example,
the human germ, primarily similar to all others, first differentiates
from vegetal germs, then from invertebrate germs, and subsequently
assumes the mammalian, placental unguiculate, and lastly the human
characters.
The development of an individual organism is at the same time a
differentiation of its parts from each other and a differentiation of
the consolidated whole from the environment; and in the last as in the
first respect there is a general analogy between the progression of an
individual organism and the progression of the lowest orders of
organisms to the highest orders.
_The Laws of Multiplication_
Every living aggregate being one of which the inner actions are adjusted
to balance outer actions, it follows that the maintenance of its moving
equilibrium depends on its exposure to the right amounts of these
actions. Its moving equilibrium may be overturned if one of these
actions is either too great or too small in amount: either by excess or
defect of some inorganic or organic agency in its environment.
Our inquiry resolves itself into this:--in races that continue to exist
what laws of numerical variation result from these variable conflicting
forces?
The forces preservative of a race are two--ability in each member of the
race to preserve itself, and ability to produce other members. These
must vary inversely--one must decrease as the other increases. We have
to ask in what way this adjustment comes about as a result of evolution.
Including under individuation all those processes completing and
maintaining individual life, and under genesis all those aiding the
formation and perfecting of new individuals, the two are necessarily
antagonistic. Every higher degree of individual evolution is followed by
a lower degree of race multiplication, and _vice versa_. Progress in
bulk, complexity or activity involves retrogress in fertility; and
progress in fertility involves retrogress in bulk, complexity, or
activity. The same quantity of matter may be divided into many small
wholes or few large wholes; but number negatives largeness, and
largeness negatives number.
It is a general physiological truth that while the building-up of the
individual is going on rapidly, the reproductive organs remain
imperfectly developed and inactive; and that the commencement of
reproduction at once indicates a declining rate of growth and becomes a
cause of arrest in growth.
It has now to be noticed how complexity of organisation is hindered by
reproductive activity and conversely. The hydra's power to produce young
ones from nearly all parts of its body is due to the comparative
homogeneity of its body, while it is not improbable that the smallness
of human fertility, compared with the fertility of large feline animals,
is due to the greater complexity of the human organisation--more
especially the organisation of the nervous system.
Of the inverse variation between activity and genesis we have examples
in the contrast between the fertility of birds and the fertility of
mammals. Comparing the large with the large and the small with the
small, we see that creatures which continually go through the muscular
exertion of sustaining themselves in the air and propelling themselves
rapidly through it are less prolific than creatures of equal weights
which go through the smaller exertion of moving about over solid
surfaces. The extreme infertility of the bat is most striking when
compared with the structurally similar but very prolific mouse; a
difference in the rate of multiplication which may fairly be ascribed to
the difference in the rate of expenditure.
_Interpretation and Qualification_
Derived as the self-sustaining and waste-sustaining forces are from a
common stock of force, it necessarily happens that, other things being
equal, increase of the one involves decrease of the other. It may
therefore be set down as a law that every higher degree of organic
evolution has for its concomitant a lower degree of the peculiar organic
dissolution which is seen in the production of new organisms.
How is the ratio between individuation and genesis established in each
case? All specialties of the reproductive process are due to the natural
selection of favourable variations. Given a certain surplus available
for race preservation, and it is clear that by indirect equilibration
only can there be established that peculiar distribution of this surplus
which is seen in each case.
Here a qualification must be made. Recognising the truth that every
increase of evolution which is appropriate to the circumstances of an
organism brings an advantage somewhat in excess of its cost, the general
law, more strictly stated, is that genesis decreases not quite so fast
as individuation increases. The result of greater individuation--whether
it takes the form of greater strength or higher speed, facilitates some
habitual movement or utilises better the absorbed aliment--is a greater
surplus of vital capital; part of which goes to the aggrandisement of
the individual and part to the formation of new individuals. Hence every
type that is best adapted to its conditions has a rate of multiplication
that insures a tendency to predominate. Survival of the fittest, acting
alone, is ever replacing inferior species by superior species. But
beyond the longer survival, and therefore greater chance of leaving
offspring, which superiority gives, we see here another way in which the
spread of the superior is insured. Though the more evolved organism is
the less fertile absolutely, it is the more fertile relatively.
_Multiplication of the Human Race_
What causes increase or decrease of genesis in other creatures causes
increase or decrease of genesis in man. It is true that, even more than
hitherto, our reasonings are here beset with difficulties. So numerous
are the inequalities in the conditions that but few unobjectionable
comparisons can be made. The human races differ not only in their sizes
and foods, and in the climates they inhabit, but also their expenditures
in bodily and mental action are extremely unequal.
The increase of fertility caused by nutrition that is greatly in excess
of expenditure is to be detected by comparing populations of the same
race or of allied races one of which obtains good and abundant
sustenance much more easily than the other. On carrying out such
comparisons it is seen that in the human race, as in all other races,
such absolute or relative abundance of nutriment as leaves a large
excess after defraying the cost of carrying on parental life, is
accompanied by a high rate of genesis.
It is also apparent that relative increase of expenditure, leaving a
diminished surplus, reduces fertility. That infertility is generally
produced in women by mental labour carried to excess is shown in the
fact that most of the flat-chested girls who survive their high-pressure
education are incompetent to bear a well-developed infant and to supply
it with the natural food for the natural period. It is a matter of
common remark how frequently men of unusual mental activity leave no
offspring.
It is likely to be urged that since the civilised races are on the
average larger than many of the uncivilised races, and since they are
also somewhat more complex as well as more active, they ought, in
accordance with the alleged general law, and other things being equal,
to be less prolific. But other things are not equal; and it is to the
inequality of the other things that this apparent anomaly is
attributable.
One more objection has to be met. Cases may be named of men conspicuous
for activity, bodily and mental, who were also noted, not for less
generative power than usual, but for more. The cases are analogous to
some before-named in which more abundant food simultaneously aggrandises
the individual and adds to the production of new individuals--the
differences between cases being that instead of a better external supply
of material there is a better internal utilisation of materials. Some
peculiarity of organic balance, some potency of the digestive juices,
gives to the system a perpetual high tide of rich blood that serves at
once to enhance the vital activities and to raise the power of
propagation. The _proportion_ between individuation and genesis remains
the same: both are increased by the increase of the common stock of
materials.
_Human Population in the Future_
Any further evolution in the most highly-evolved of terrestrial
beings--man--must be of the same nature as evolution in general. It must
be an advance towards completion of that continuous adjustment of
internal to external relations which was shown to constitute life.
Looking at the several possibilities, and asking what direction this
further evolution, this more complete moving equilibrium, this better
adjustment of inner to outer relations, this more perfect co-ordination
of action is likely to take:--the conclusion is that it must take mainly
the direction of a higher intellectual and emotional development. There
is abundant scope for development in ascertaining the conditions of
existence to which we must conform; and in acquiring a greater power of
self-regulation.
What are those changes in the environment to which, by direct or
indirect equilibration the human organism has been adjusting itself, is
adjusting itself now, and will continue to adjust itself? And how do
they necessitate a higher evolution of the organism? In all cases
pressure of population is the original cause. Were it not for the
competition this entails, so much thought and energy would not be spent
on the business of life; and growth of mental power would not take
place. Difficulty in getting a living is alike the incentive to a higher
education of children, and to a more intense and long-continued
application in adults. Nothing but necessity could make men submit to
this discipline; and nothing but this discipline could produce a
continued progression.
Excess of fertility is then the cause of man's further evolution. And
the obvious corollary is that man's further evolution itself
necessitates a decline in his fertility. The further progress of
civilisation will be accompanied by an enhanced cost of individuation:
whether it be in greater growth of the organs which subserve
self-maintenance, in their added complexity of structure, or in their
higher activity, the abstraction of the required material, implies a
diminished reserve of materials for race maintenance. This greater
emotional and intellectual development does not necessarily mean a
mentally laborious life--for, as the goal becomes organic, it will
become spontaneous and pleasurable.
The necessary antagonism of individuation and genesis not only fulfils
the _a priori_ law of maintenance of the race from the monad up to man,
but insures final attainment of the highest form of this maintenance--a
form in which the amount of life shall be the greatest possible and the
births and deaths as few as possible. From the beginning pressure of
population has been the proximate cause of progress. After having duly
stocked the globe with inhabitants; raised all its habitable parts into
the highest state of culture; brought all processes for the satisfaction
of human wants to perfection; developed the intellect into complete
competency for its work, and the feelings into complete fitness for
social life; the pressure of population as it gradually finished its
work, must gradually bring itself to an end.
Changes, numerical, social, organic, must by their mutual influences
work unceasingly towards a state of harmony--a state in which each of
the factors is just equal to its work. And this highest conceivable
result must be wrought out by the same universal process which the
simplest inorganic action illustrates.