Among questions bearing upon it but not directly attacking it has
been the discussion of the individual difference. For example, are
differences due to individual experiences ever inherited? Or are
only inherent differences transmissible? What rôle is played by what
one might call “normal,” relatively slight differences, and what
by the “sports” and abnormal births in specific change? Do species
under stress, and feeding on strange food or living in unaccustomed
climates, betray any exceptional tendency to produce abnormality? Have
there been, so to speak, storms and riots of variation in some cases?
Can differences establish themselves while outer necessity remains
neutral? Can variations amounting to specific differences in colour
and form arise as a sort of play of the germ plasm and be tolerated
rather than selected by nature? In what manner do normal differences
arise? What happens to differences in cases of hybridisation? Here are
sample questions that have been the seeds of splendid work and great
arguments. Some of them were already under discussion in Darwin’s time;
he was a pioneer in such explorations; many ideas of his have stood the
test of time, and many suggestions he threw out have been disproved.
When some casual “may be” of Darwin’s is examined and set aside, it
is the custom of polemical journalists to rush about and proclaim to
all who may be sufficiently ill-informed to listen that Darwin is
“exploded.” Such explosions of Darwin are constantly recurring like
gun-fire near a garrison town, and still he remains. None of these
subsidiary questions affect the stability of this main generalisation
of biology, the Theory of Natural Selection.
The actual attack and testing of the Theory of Natural Selection
have yielded negative results. The statement of the theory may have
been made finer and exacter, that is all. And yet the conditions of
its survival have been very exacting. If the theory is to stand, the
whole of plant and animal life in time and space must be arranged in
a certain order. It must be possible to replace classification by a
genealogical tree. Every form must fall without difficulty into its
proper place in that tree. If it is true that birds are descended
from reptiles or men from apes, then there must be no birds before
the reptiles appear, and no men before apes. The geological record is
manifestly a mere fragmentary history, still for the most part unread,
but, however fragmentary it is, it must be consistent. One human skull
in the coal measures blows the whole theory to atoms. The passage
from form to form must be explicable by intermediate types capable of
maintaining themselves; there may be gaps in the record, but there must
be no miraculous leaps in the story. If an animal living in the air is
to be considered as a lineal descendant of some animal living in the
water, then the structure of the former bit by bit and step by step
must be shown to be adapted, modified, changed about from that of the
latter; it must have ears for water-hearing modified for air-hearing,
and its heart and breathing arrangements must be shown to be similarly
changed over, and so on for all its structure. All these requirements
will follow naturally from the necessities of a process of Natural
Selection. They follow logically upon no other hypothesis. They are not
demanded, for example, by the idea of a Creator continually interfering
with and rectifying some stately, unaccountable process of “Evolution,”
which seems to be Mr. Belloc’s idea--so far as he ventures to display
any idea of his own--in the matter. Such things as vestigial structures
and a number of odd clumsinesses in living things--many still very
imperfect adaptations to an erect position, for example--become
grotesque in relation to such a view. A Creator who put needless or
inconvenient fish structures into the anatomy of a land animal and
made the whole fauna and flora of the land a patch-up of aquatic forms
of life must be not so much a Divinity as a Pedant. But it is the
burthen of the whole beautiful science of comparative anatomy that the
structure of animals and plants, and their succession in time, fall
exactly into the conditions defined by the Theory of Natural Selection.
In the most lovely and intricate detail, in a vast multitude of
examples, in plants and in animals alike, this theme of the adaptation
of pre-existing structure is worked out.
We should in accordance with the Theory of Natural Selection expect
to find traces of the ancestral form, not only in the lay-out of the
adult animal, but in every phase of its life history, and that, in
fact, is just what we do find. There is no more fascinating branch of
comparative anatomy than embryology. Each life cycle we discuss tends
to repeat the ancestral story, and only under the stress of necessity
does it undergo modification at any point. There is little toleration
in the life process for unnecessary divergencies. Economies are
effected by short cuts and reductions, and special fœtal structures are
granted reluctantly. So that even in man we find peeping through the
adaptations imposed upon the human type by its viviparous necessities,
and in spite of the advantage of every economy of force, memories,
for example, of the gill slits, of the fish heart and kidney, of the
reptilian skull, of the mammalian tail. I mention this fact in the
_Outline_, and upon it Mr. Belloc comments in a manner that leaves
one’s doubts poised between his honesty and his intelligence. He
declares, which is totally untrue, that I “repeat the old Victorian
tag”--I doubt if there ever was such a tag--that the embryo “climbs up
the family tree.” He puts these words in inverted commas as though I
have really adopted and used them, and for the life of me it is only by
straining my charity to the utmost that I can accept that this was an
accident. Of course every text-book of embryology for the last forty
years has made it perfectly plain, as I have stated here, that the life
cycle can be and is modified at any point, and that an embryo has much
more serious work in hand than reciting its family history. It betrays
its ancestral origins to analysis; but that is an altogether different
matter. Mr. Belloc, however, is so densely ignorant himself upon these
questions that he can imagine, or think it worth while to pretend to
imagine and attempt to persuade his readers by the expedient of these
inverted commas, that I entertain such a view. And then follow this,
which I quote that the reader may the better understand a certain
occasional acerbity in my allusions to Mr. Belloc:--
“He doesn’t know that Vailleton of Montpellier has knocked the
last nail into the coffin of that facile and superficial Victorian
shortcut (and blind alley). He has probably never heard of
Vailleton, and when he does he will suspect him for a foreigner.
That is what I mean by being provincial and not abreast of one’s
time.”
It is perfectly true that I have never heard of any Vailleton in
biological science. Nor has anyone else. There is “no sich person.”
Perhaps Mr. Belloc has not been able to read the manuscript of some
adviser, or his memory may have played a trick upon him. Possibly he
has in mind that eminent Victorian embryologist, Vialleton, who, so far
from being the very newest thing in “European” biology, must now be
getting on for seventy. He is half-way back to Haeckel, the originator
of the family-tree idea, a German embryologist and not, as a matter
of fact, the Victorian English Protestant Mr. Belloc supposes him to
be. Possibly years and years ago some French student may have run away
with the idea that embryos conscientiously repeat their phylogeny,
and Professor Vialleton may have thought it well to discuss this idea
in one of his books. It is not an idea I have ever entertained, much
less stated, and its only interest here is that it gives Mr. Belloc a
chance of showing how rudely he can set out his inaccuracies and his
misconceptions.
But this is an incidental comment. I will reserve for my next section
a consideration of the remarkable arguments--“crushing arguments” the
enthusiastic cross-heads of his editor declare them to be--that Mr.
Belloc produces against this view of life as being in a state of change
under the action of Natural Selection, that I have put here before the
reader.