an impressive scale the power of the historical method. Natural
development, determined by unalterable conditions, was with him the
key to the right understanding of the past. It is well known that here
and there a great thinker had before Montesquieu framed something like
the same conception. The Politics of Aristotle[18] and Vico's study
of the historical evolution of the Roman law (1725) are memorable
anticipations. By 1748, the date of the _Esprit des Lois_, or 1749,
the date of Buffon's first volumes, which come next before us, Newton's
_Principia_ had made students of physics and astronomy practically
familiar with the notion of universal causation.
Buffon's place in the history of science is that of one who
accomplished great things in spite of weaknesses peculiarly alien to
the scientific spirit. It was mainly he who, by strenuous exertions
and largely at his own cost, transformed the gardens from which the
king's physicians used to procure their drugs into what we now know
as the Jardin des Plantes. By the untiring labours of fifty years he
produced a Natural History in thirty-six volumes crowded with plates.
Having won for himself a place side by side with Montesquieu and
Gibbon, he employed it to direct attention to the larger questions of
biology and geology. He was a pronounced freethinker, who promulgated
bold views with a dexterity which saved him from condemnation by the
theological tribunals. When his opinions were declared to be contrary
to the teaching of the Church, he printed a conciliatory explanation,
but never cancelled the passages objected to, which continued to appear
in a succession of editions. His deficiencies, we must admit, were
serious. He was a poor observer (partly because of short sight), and
had no memory for small details. His enemies were able to taunt him
with absurd mistakes, such as that cows shed their horns. He alienated
the two foremost naturalists of the eighteenth century, Linnæus and
Réaumur, by ignorant and scornful criticisms. His strong propensity
to speculation, insufficiently checked by care to verify, might have
brought him under the sarcastic remark of Fontenelle, that ignorance
is less apparent when it fails to explain _what is_, than when it
undertakes to explain _what is not_.
Buffon's fame is not seriously impaired by the fact that his great work
is no longer read except by those who study the course of scientific
thought. Few productions of the human intellect retain their value
after a hundred years, and scientific treatises become obsolete sooner
than others. It is consoling to recollect that, if their energy is
quickly dissipated, it is at least converted into light.
In a history of biology Buffon is naturally a more important figure
than Montesquieu. Buffon had imbibed evolutionary views from the
_Protogæa_ of Leibnitz, which in turn made use of certain hypotheses
of Descartes.[19] The _Histoire Naturelle_ inclines to some theory of
evolution, especially in the later volumes. At first Buffon teaches
that species are fixed and wholly independent of one another; some
years later he is ready to believe that all quadrupeds may be derived
from some forty original forms, while in a third and subsequent passage
he puts the question whether all vertebrates may not have had a common
ancestor. He does not shrink from saying that one general plan of
structure pervades the whole animal kingdom—a belief that he could
never have adequately supported by facts; Baer long afterwards (1828)
searched in vain for evidence on this very point, while Darwin in
1859 admitted that his arguments and facts only proved common descent
for each separate phylum of the animal kingdom;[20] he inferred _from
analogy_ that probably all the organic beings which have ever lived on
this earth have descended from some one primordial form.[21] Elsewhere
Buffon makes bold to declare that Nature in her youthful vigour threw
off a number of experimental forms of life, some of which were approved
and adopted, while others were allowed to survive in order to give
mankind a wider conception of her projects. There is generally some
gleam of truth in Buffon's most fantastic speculations, but we often
wish that he could have attended to the warning of Bossuet: "Le plus
grand dérèglement de l'esprit est de croire les choses parce qu'on veut
qu'elles soient."
[Illustration: GEORGES LOUIS LECLERC, COMTE DE BUFFON.]
Against all his shortcomings we must set the fact that Buffon strove
to interpret the present by the past, the past by the present, geology
by astronomy, geographical distribution by the physical history of the
continents. One of his maxims expresses the fundamental thought of
Lyell's _Principles of Geology_: "Pour juger de ce qui est arrivé,
et même de ce qui arrivera, nous n'avons qu'à examiner ce qui arrive."
Hard-and-fast distinctions are the marks of imperfect theory. Early
philosophers distinguished hot and cold, wet and dry, light and dark,
male and female, as things different in kind. In later times organic
and inorganic, animal and vegetable, the activities of matter and the
activities of mind, have been sharply separated. But as knowledge
increases these distinctions melt away; it is perceived that the
extreme cases are either now connected by insensible gradations, or
else spring historically from a common root. Hutton, Lyell, and their
successors have made it clear that the history of the earth calls for
no agents and no assumptions beyond those that are involved in changes
now going on; the present is heir by unbroken descent to the past.
Continuity has been established between all forms of energy. Even the
chemical elements, once the emblems of independence, give indications
that they too had a common origin. The nebular hypothesis, which has
been steadily rendered more probable by the scientific discoveries of
two centuries, traces all that can be perceived by the senses to a
homogeneous vapour, and lays the burden of proof on those who believe
that continuity has its limits. Every history, whether of planetary
systems, or of the earth's crust, or of human civilisations, religions,
and arts, is recognised as a continuous development with progressive
differentiation.
Amateur Students of Living Animals.
A history of biology would be incomplete which took no notice of
every-day observations of the commonest forms of life. Some of the best
are due to the curiosity of men with whom natural history was no more
than an occasional recreation. William Turner (a preacher, who became
Dean of Wells), Charles Butler (a schoolmaster), Caius and Lister
(physicians), Claude Perrault (a physician and architect), Méry and
Poupart (surgeons), Frisch (a schoolmaster and philologue), Lyonet (an
interpreter and confidential secretary), Roesel (a miniature painter),
Henry Baker (a bookseller, who gained a competence by instructing deaf
mutes), Leroy (ranger to the King of France), Stephen Hales, Gilbert
White and William Kirby (country parsons), and William Spence (a
drysalter) were all amateurs in natural history. To this list we might
add Willughby, Ray, Leeuwenhoek, Réaumur, De Geer, Buffon, the Hubers,
and George Montagu, who were either so fortunate in their worldly
circumstances or so devoted to science as to make it their chief, or
even their sole pursuit, though they did not look to it for bread.
A large proportion of the naturalists whose names have been quoted
occupied themselves with the habits and instincts of animals, and
biology has been notably enriched by their observations. To Englishmen
the most familiar name is that of Gilbert White, in whom were combined
thirst for knowledge, exactness in description, and a feeling for the
poetry of nature.
White used his influence to encourage what may be called _live natural
history_, which, as he understood it, "abounds in anecdote[22] and
circumstance." He bids his correspondents to "learn as much as possible
the manners of animals; they are worth a ream of descriptions." His
example has done more than his exhortations. He focusses a keen
eye upon any new or little-known animal, such as the noctule, the
harvest-mouse, or the mole-cricket; detects natural contrivances
little, if at all, noticed before, such as the protective resemblance
of the stone-curlew's young; dwells upon the practical applications
of natural history, such as the action of earthworms in promoting
the fertility of soils; and combines facts which a dull man would be
careful to put into separate pigeon-holes, such as the different ways
in which a squirrel, a field-mouse, and a nuthatch extract the kernels
of hazel-nuts.
The many amateurs of the eighteenth century naturally demanded books
written to suit them, and illustrated books with coloured plates,
coming out in parts, found a ready sale. Some were devoted to insects,
others to microscopic objects. In accordance with prevalent belief, the
writers made a point of tracing the hand of Providence in the minutest
organisms; many popular treatises were altogether devoted to natural
theology. Some few of these natural history miscellanies contained
original work, which has not yet lost its interest. The best is
Roesel's _Insecten-belustigungen_ (four vols. 4to., 1746-61),
memorable among other things for containing the original description of
Amœba. For English readers Henry Baker wrote _The Microscope Made
Easy_ (1743) and _Employment for the Microscope_ (1753).
Intelligence and Instinct in the Lower Animals.
The period with which we are now concerned (1741-1789) initiated the
profitable discussion of the mental powers of animals. We are unable
for lack of space to follow the investigation from period to period,
and must condense into one short section whatever its history suggests.
In the year 1660 Aristotelians were still discoursing about the
vegetative and sensitive souls which bridged the gulf between inanimate
matter and the thinking man. Descartes had tried to prove that the
bodies of men and animals are machines actuated by springs like
watches. Man, however, according to Descartes, possesses a soul wholly
different in its properties from his body, and apparently incapable of
being acted upon by it. Man only can think; animals are capable only
of physical sensations, and have no consciousness. Into speculations
like these we shall not venture, being- content, like Locke, "to sit
down in quiet ignorance of those things which upon examination are
proved to be beyond the reach of our capacities." We shall merely note
here and there facts ascertained by observation or experiment, and
plain inferences drawn from such facts.
Swammerdam and Réaumur, besides many naturalists of less eminence,
recorded a host of observations on the activities of insects. They
contributed little to the discussion except new facts, for habit led
them to ascribe without reflection every contrivance to the hand of
Providence or else to Nature. Some of their facts, however, made a
deep impression, none more than the exact agreement of the cells
of the honeycomb with the form which calculation showed to be most
advantageous.[23] The coincidence has lost some of its interest since
the discovery that the theoretically best form of cell is hardly ever
realised.[24] Réaumur,[25] in describing the process by which a certain
leaf-eating caterpillar makes a case for itself out of the epidermis
of an elm-leaf, showed that the caterpillar is not devoid of that kind
of intelligence which adapts measures to circumstances. He cut off the
margin where the upper epidermis of the leaf passes into the lower
one, a margin which the insect had intended to convert into one side
of its case; the caterpillar sewed up the gap. He cut off a projection
which was meant to form part of the triangular end of the case; the
caterpillar altered its plan, and made that the head-end which was
originally intended to lodge the tail. This observation anticipates a
better-known example taken from the economy of the hive-bee by Pierre
Huber, which is mentioned below.
Buffon[26] heard with impatience all expressions of admiration for
the works of insects. His poor eyesight and his repugnance to minutiæ
disinclined him to pay much attention to creatures so small, and he had
set himself up as the rival of Réaumur in physics and natural history.
To pour contempt upon insects gratified both feelings at once. Bees, he
said, show no intelligence at all; their actions are purely automatic,
and their much-vaunted architecture is merely the result of working in
a crowd. The cells of the honeycomb are hexagonal, not by reason of
forethought or contrivance, but because of mutual pressure; soaked peas
in a confined space form hexagonal surfaces wherever they touch.
The elder Huber seems to have denied to bees every trace of
intelligence, but his son Pierre found it hard to go so far.[27] He
remarked that the storage-cells of a honeycomb are not always exactly
alike; they may be lengthened, cut down, or curved, when requisite.
Cells which had been rudely trimmed with a knife were repaired with
such dexterity and concert as to suggest that even the hive-bee has
"le droit de penser." Bees would under compulsion build upwards or
sideways, instead of downwards, as they like to do. Finding that they
sought to extend their combs in the direction of the nearest support,
he covered the support with a sheet of glass, on which they could get
no footing. They swerved at once from the straight line, and prolonged
their comb towards the nearest _uncovered_ surface, though this obliged
them to distort their cells. He was driven to the conclusion that bees
possess "a little dose of judgment or reason." In our own time, when
all conscious adaptation of means to ends is believed to be worthy of
the name of _reason_, it requires no great courage to ask why we deny
such an attribute to all the lower animals.
In spite of examples like this, the favourite expression "blind
instinct" helped to strengthen the conviction that the mental processes
of animals are unsearchable. It is impossible to deny that the epithet
_blind_ is appropriate in many cases. A bird will sit an addled egg
all summer, or vainly but repeatedly attempt to make its tunnel in the
insufficient breadth of a mud wall (Geositta). Of course such instances
do not show that _all_ the acts of the lower animals are devoid of
intelligence.
Hume in 1739 and again in 1748 appealed to everyday observation of
dogs, birds, and other animals of high grade. The facts seemed to him
to show that animals as well as men are endowed with reason and able
to draw inferences; he did not, however, credit them with the power of
framing general statements, holding that experience operates on them,
as on children and the generality of mankind, by "custom" alone. It is
notorious that the dog and other higher animals learn by experience;
Hume tells, for instance, how an old greyhound will leave the more
fatiguing part of the chase to younger dogs, and place himself so as
to meet the hare in her doubles. On the other hand (though Hume does
not say so) man himself possesses non-educable instincts. In short,
Hume sees no ground for drawing a line between the mental powers of man
and those of the higher animals, though he attributes to man a power
of demonstrative reasoning to which animals do not attain. In this he
substantially agrees with Aristotle,[28] who maintained that in animals
the germs of the psychical qualities of the man are evident, though,
as in the child, they are undeveloped. Hume's teaching also accords
with modern views; comparative anatomy, for instance, "is easily able
to show that, physically, man is but the last term of a long series of
forms, which lead by slow gradations from the highest mammal to the
almost formless speck of living protoplasm, which lies on the shadowy
boundary between animal and vegetable life."[29]
The detailed proofs which Hume was not enough of a naturalist to
furnish were at length stated with admirable clearness and force by
Leroy, whose _Letters on Animals_ form the most important contribution
made to the discussion during our period. Georges Leroy ( 1723-1789)
was _lieutenant des chasses_ under the last French kings, and had
charge of the parks at Versailles and Marly. He wrote therefore with
knowledge about the wolf, fox, deer, rabbit, and dog. His pages are
enlivened by many touches of nature, interesting to readers who perhaps
care little about psychology. Leroy attributes to the wolf observation,
comparison, judgment. The wolf must mark the height of the fold which
encloses a flock, and judge whether he can clear it with a sheep in his
mouth. Wolf and she-wolf co-operate artfully in the running-down of
prey. Sometimes the she-wolf will draw off the sheep-dog in pursuit,
thus putting the flock at the mercy of her mate. Or one of the two will
chase the quarry till it is out of breath, when the other can take up
the running on advantageous terms. An old fox shows knowledge of the
properties of traps, and will rather make a new outlet or suffer long
famine than encounter them. But when he finds a rabbit already caught,
he realises that the trap has lost its power to hurt. Sheep-dogs can
be educated to mind things which do not interest wild dogs, or dogs of
other breeds; when, for instance, the flock is driven past a patch of
wheat, the dog in charge will take care that the sheep do not damage
the crop. A trained sporting-dog learns at length to trust his own
judgment, even in opposition to that of his master, and sportsmen
know that they must direct young dogs, but leave old ones to act for
themselves.
From the middle of the eighteenth century to the present day
naturalists and psychologists have been labouring to distinguish
instinct from intelligence. It is not hard to define well-marked
examples of each, and to show that a typical instinct is _congenital_
(not the result of a process of education or self-education),
_adaptive_ (conducive to the welfare of the organism), _co-ordinated
by nerve-centres_ (thus excluding the superficially similar behaviour
of the lowest animals and all plants), _actuating the whole organism_
(thus excluding most, if not all, reflex acts in the higher animals,
as well as the wonderful adjustments effected by bone-corpuscles
and other parts of organisms), and _common to all the members of a
species or other group_ (thus excluding individual aptitudes).[30]
In the same way it is easy to point out clear differences between a
bird and a tree. But just as a definition which shall separate every
animal from every plant has hitherto been sought in vain, so it has
hitherto been impossible to frame a definition which while including
all instincts shall admit no case of reflex action or intelligence. The
most ambiguous cases of all are perhaps to be found in insects, where,
as will shortly be explained, our information is ill-fitted to support
precise distinctions.
Many naturalists entertain some form of what may be called the
_use-and-disuse_ or _inherited-memory_ theory, supposing that
the aptitudes of the offspring are influenced by the activities of
the parent. Some cling to the belief that habits can be fixed and
transmitted, and we must admit that the fixation and transmission of
habits might explain a great deal. But all the evidence goes to prove
that habits are not inherited at all, and that we must look elsewhere
for the origin of instincts. Let naturalists who think differently try
to account for the instincts of working bees or ants, which receive
their psychical not less than their physical endowment from a long
succession of ancestors, none of which worked for their living. Or let
them try to explain the instances of spiders, insects, etc., which
_after egg-laying_ practise instinctive arts for the defence of
their brood, standing over the eggs, carrying them about, blocking the
entrance of the burrow, etc. May we not say that it is impossible for
the acts of a parent to influence the congenital instincts of offspring
which have already lost connection with the mother? But surely a theory
of instinct breaks down which fails to account for the expedients by
which the worker-bee, the worker-ant, and the spider provide for the
safety of the unhatched brood or for the welfare of the community.
Darwin's _Origin of Species_ threw a new light upon instinct
by showing that natural selection can operate on the subtlest
modifications. It can discriminate shades of hardiness to climate,
shades of intellectual acuteness, or shades of courage. It can
intensify qualities which appear only in adults past bearing or in
individuals congenitally incapable of propagation. Human selection,
though a blunt tool in comparison with natural selection, can originate
a bold and hardy race of dogs, or showy double flowers incapable of
producing seed. In the second case fertile single flowers continue the
race, as in the garden Stock. Darwin pointed out that the barren double
flowers of the Stock answer to the workers of social bees and ants,
the fertile single flowers to the functional males and females. Every
modification that works to the advantage or disadvantage of the race,
whether we classify it as physical, intellectual, or moral, gives scope
for the operation of natural selection.
The comparative psychology of small invertebrates, such as insects,
is impeded by our imperfect knowledge of their nervous physiology.
Introspection is here impossible; experimental physiology and
pathology, which have done so much for the psychology of the higher
vertebrates, almost impossible; analogy is a treacherous guide where
the structures involved differ conspicuously. We have little to guide
us in the psychology of insects except their behaviour, and that is
often capable of a variety of interpretations. The only course is
to adopt Pasteur's watchword, "Travaillons!"—the difficulties will
diminish with time and labour.
The Food of Green Plants.
Common observation taught men in very early times that green plants
draw nourishment from the soil, and that sunlight is necessary to
their health. In the age of Galileo a Belgian physician and chemist,
Van Helmont, endeavoured to pursue the subject by experiment. He
planted the stem of a live willow in furnace-dried earth, which was
enclosed in an earthen vessel. Rain-water or distilled water was
supplied when necessary, and dust excluded by a perforated lid. The
loss of weight due to the falling-off of leaves was neglected. In
the course of five years the tree was found to have increased to
more than thirty times its original weight; Van Helmont concluded
that this increase was due to water only. Malpighi (1671), being
guided mainly by his microscopic studies of the anatomy of the stem
and leaf, taught that moisture absorbed by the roots ascends by the
wood, becoming (apparently at the same time) aerated by the large,
air-conducting vessels; that it enters the leaves, and is there
elaborated by evaporation, the action of the sun's rays, and a process
of fermentation; lastly, that the elaborated sap passes from the leaves
in all directions towards the growing parts. It will be seen that this
explanation, though incomplete, makes a fair approximation to the
beliefs now held; for more than a hundred years after Malpighi's day
less instructed opinions were commonly held. Hales (1727) recognised
that green plants are largely nourished at the expense of the
atmosphere; he dwelt also on the action of the leaves in drawing water
from the soil, and in discharging superfluous moisture by evaporation.
Joseph Priestley, who had been proving that air is necessary both to
combustion and respiration, made an experiment in 1771 to discover
whether plants affected air in the same way that animals do. He put
a sprig of mint into a vessel filled with air in which a candle had
burned out, and after ten days found that a candle would now burn
perfectly well in the same air. Air kept without a plant, in a glass
vessel immersed in water, did not regain its power of supporting
combustion. Balm, groundsel, and spinach were found to answer just as
well as mint. Air vitiated by the respiration of mice was restored by
green plants as readily as air which had been vitiated by combustion.