DARWIN'S THEORY

Evening Post, Volume CXXV, Issue 18, 22 January 1938, Page 6

DARWIN'S THEORY

UNDER FIRE AGAIN

NEW LIGHT ON EVOLUTION

FROM LIVING ORGANS

Though Darwin's theory of natural selection as the cause of evolution is part of the scientific gospel in which nearly every biologist believes, it has been under fire for years, says the "New York Times." Huxley, Darwin's most ardent supporter and champion, told his master that the lack of experimental proof was the weakest point in the case of natural selection. And Dar'win himself was puzzled enough to write 'to Huxley, "if as I must think, external conditions produce little effect, what the devil determines each particular variation?" Since Darwin thus expressed his bewilderment some of the experimental work demanded by Huxley has been1 done. The, Abbe. Gregor Mendel per-| formed his now classic breeding ex-1 periment with sweet peas and laid down his famous Mendelian law of heredity; X-rays have been shot at the eggs of fruit flies and monstrosities hatched which are true new species; Nobel Prize winner Morgan elaborated the theory of the gene, wnich bears' about the same relation to life that the atom does to.dead matter, Ihe mechanism of evolution is nevertheless as dark a mystery as ever. There is.still room for theorising, at.a theories enough have been forthcoming

One of the theorists is Ibe distinguished British naturalist, Professor W. P. Pycraft. In a paper of his which is reprinted in ihe annual >-epprt of the Smithsonian Institution he presents the idea that evolution' occurred through- use of. organs as a supplement to - the Darwinian scheme .of natural selection and the Lamarckian conception of adaptation to environment. Neither Darwin nor Lamarckian, he holds,, explains the enormous diversity of living forms.

MOULDING OF. BODY.

i According to Professor Pycrnfl the bedyis moulded by the diversion of food to those organs wlivh are most ' stimulated by ordinary activities. Consequently growth is biased, meaning that; the favoured organs develop at the expense of others. 1 "We are to regar.l the various types !of animals as self -regulating organ'isms, moulded by foe effects ofp^Tsist'ent stimuli sustained by their several organs, or parts of organs, which thus become shaped for use in, the higher animals under the controlling agency of the sympathetic nervous system," he explains. "But insamuch as living tissue is-in no two organisms precisely alike in its qualities it follows.that this 'use' will manifest itself in different ways. The tissues which are used most will take up most of what we call 'food material,' growth being determined by the measure of use. But in this process of growth, in course of time., the form of the whole body, may become materially changed."

Professor Pycraft maker much of the two kinds of germ plasvn in which biologists believe. First there is germ plasm. This is the hereditary stuff, which passes on from parents to progeny to the uttermost generation and which contains the genes that determine whether we shall be tall or short, blondes or brunettes, yellow or white. i Genes are hypotheses, like atoms. No one has ever seen either a gene or,an atom—or ever will see one.

The other kind of plasm is the somato or body plasm—the stulf out of which the genes mould men, trees, anything that lives. This somato or body plasm is not passed on as such to the next generation. It dies. In fact, what we call death is the death of the body, alone—not of the transmissable gene.

OBJECTS TO PLASM,

Professor Pycraft objects to this distinction in plasms. He finds it impossible to draw the line between the two. As an example he points to the amoeba, a microscopic one-celled creature. It reproduces by the simple process of splitting in two. AH its protoplasm takes part in this process.

"If we say," reasons Dr. Pycraft, "amoeba is ..composed solely of 'germ plasm1 or. of we are merely making a distinction without a difference. But if ' the substance which forms the1 body of the proto.zoati.can reproduce other-like bodies i indefinitely .we need' ask ho moreV' ~iThe question is further coinplicat|ed by the ease with which many | plants reproduce either by seeds or by grafts and rooting of slips. Nobody has ever maintained that the slips contain any germ plasm or any genes —only somatoplasm. Yet the slipped plant; which has no,transmitted germ plasm, contains' all the characters of its race and will- bear itself seeds.

Professor Pycraft boldly.throws overboard the accepted theory that somatoplasm is derived . from the germ plasm. The contrary, is true, he holds. The somatoplasm is specialised for the purpose of transmitting characters to descendants in the course of the deyelopment of the individual just as other somatoplasm, forming the brain or the nose or other parts of the body, are specialised to serve definite functions.

If Professor Pycraft is right the Mendclian hypothesis of. units of heredity must go. .'He admits that it has proved very" useful to the plant and animal breeder, inasmuch as it has made it possible to predict what the offspring of matings of known ancestry will be.. Undismayed, he "suggests that these results would be as easily explained as due to the mingling of slightly di£J ferehf strains of somatoplasm." ',"'• DEMANDS 'ON BELIEF.

To this observer it seems that the doctrine of descent makes strong demands on logic and belief;' It'calls upon heredity to explain resemblances in related species. Then it turns around and denies the validity of the laws of heredity by allowing species to vary.

Professor Pycraft's theory overcomes this objection by postulating the diversion of. nourishment to favoured organs. But there are other objectionsobjections that' have been advanced I time and time again by 'anti-Darwin-ians. Evolution, as ; both Darwin and Professor Pycraft conceive it,: is supposed to proceed by minute steps. The sum •of these eteps . becomes evident only after the lapse of hundreds of thousands of years. This being so; fossils ought to present a very different picture of evolution than they do; Takethe famous series of leg and foot bones that show the evolution of the horse from a five-toed animal about as big as a St. Bernard dog to" thd draft Percheron or the fast-running animal of today. There1 are no con-i. tinuous transformations, but jumps.. Never is it possible to trace "evolution by a set of easy stages.;' ■:■'■■■■* ■ '■■ ::

This holds true even for-such erea-* ture's as the Archeopteryx, which is a missing link between reptiles and birds and which looks good from the theory of descent. Yet Archeopteryx does not completely fill the gap between the birds and the- reptiles. In fact, when new reptile-like or birdlike fossils are found the zoologists and paleontologists classify them either