THEORY OF EVOLUTION

Gisborne Times, Volume LVIII, Issue 9670, 17 April 1923, Page 3

THEORY OF EVOLUTION

' DARWINISM TO-DAY,

1 'L’OCTRIK-i OF NATURAL SELF ; , TION 'QRITiCISFi), s • (By Professor W. E. Agar, in the 1 Melbourne Argus.) 1 It is given to but few mortals to > influence the thoughts and imaginar. tion of mankind so profoundly as did ' Charles Darwin by lii's establishment of /the doctrine of organic evolution. Even those to whom the speculations ! of pure science have, as a rule, little attraction, must take an intense personal ii terest in a doctrine which professes to throw such a vivid light on the most fundamental problems of human nature. The idea of organic evolution, though always associated with the name of Darwin, is a very old one, being met with even among the Greeks. Till Darwin’s time, however, it remained only a speculation, but in his hands the doctrine of evolution : received a shape that soon compelled : general acceptance. With painstaking labor, extending over many years, lie collected and weighed evidence along many separate lines, which establish- ' ed beyond reasonable doubt the his- ; torieal fact of evolution—that is to say, that tho enormously varied and , complex system of animate nature, of 1 which we form a part, has been pro- : duced by a process of transformation : and elaborations of a few (or possibly I of only one), simple primordial beings, j Not only did Darwin establish the ! fact of evolution ; he propounded his , famous theory of natural selection as | as explanation of how this evolution j had been brought about. When we hear, as wo sometimes do, that Darj wiriism no longer holds the position [ in the scientific world that it did 20 j years ago, it is well to remember that : if there is any truth in tin’s state- : ment, it is only in regard to the doc- ; trine of natural selection, not to the ■ historical fact of evolution itself. This j fact, it is not too much to say, has become more firmly established with every year that has elapsed since the publication of "The Origin of Species.” Nor can the very great inrport- : anco of the principle of natural seleci tion ho questioned; hut it is, perhaps, I true that modern research has in- : creased, rather than diminished, the difficulties which a section of biologists have always felt in accepting the doctrine in the extreme form which was popular for a generation after Darwin’s time. Natural Selection. The starting point of Darwin’s j theory of natural selection was the | observed fact that even closely related members of the same species are not absolutely identical with one another, but exhibit little personal differences, such as we are familiar with

amongst the members of our own species. Now it is also an observed fact that animals in a state of nature produce far more young than circumstances can permit to survive. (For »the total number of animals in the world does not increase progressively from year to year, so on an average each pair of animals can only leave two descendants.) On the whole, the survivors will generally be those whose individual peculiarities best suit them to their environment. A third observed fact, that individual peculiarities are, to some extent at any rate, inherited showed Darwin that the operation of this principle through a large number of generations must produce an indefinite alteration of the original type. Moreover, the almost infinite different kinds of environment would in course of time result among the descendants of a single pair in an indefinitely varied assortment of animals to suit these environments. Now it seems plain that while tiie operation of this principle must result in a large measure of evolution—that is to say, production of varied and beautifully adapted organisms 'from a single primordial living being —the nature of the organisms produced must depend primarily on the nature of those individual, inheritable peculiarities which form the raw material on which natural selection has to operate. At the outset there is one cause of individual . differences which can be disposed of for the purposes of our argument. That is, differences caused by the direct reaction of organisms to their environments. Besides the fact that it is extremely doubtful whether the Effects of such reactions are inherited, the real problems of evolution are independent of this principle. Consider•only the case of the eye. By what conceivable direct action of environment would the cornea and lens (both of which are formed from tlie skin) have been rendered transparent? Indeed, we know that the .passage of rays of light through the skin has exactly the opposite effect —it renders it more opaque, as wo experience every time we get sunburnt. Nor is it understandable how the mere passage of rays of light, or any internal activity of the eye, connected with vision, could have shaped the cornea into a segment of a sphere, and the lens into a biconvex disc. Tims the origin of the individual variations which formed' the stages by which the eye (to take only one example) was evolved must find some other explanation than the direct moulding effect of environment. Individual Peculiarities. The outstanding problem for the evolutionist is, therefore, the nature of the little individual peculiarities which constitute the differences between members of the same species or family. To Darwin, this diversity was the expression of an inherent instability, of an inherent tendency to vary, on tlie part of living organisms. According to this view, each step gained in tlie process of evolution formed a centre around * which new variations took place, and so evolution could be visualised as a continuous process. Modern experimental work, however, founded the epoch making work of Mendel,' has given us a different picture of the nature of organic diversity. It conceives of ; the composition of the hereditary ; substance out of a large number of | elementary living units, sometimes 1 referred to as hereditary factors, | which are differentiated from each | other, and all of which co-operate in I the production of the organism. The 1 diversity existing between nearly related animals is not an expression of their instability, but rather is caused by different combinations of these elementary units, which are themselves believed (as the result of experimental work) to be very stable bodies. It is true that they can, and sometimes do, change their nature—but this change (spoken of as a mutation) is rare, and : contributes very little to tlie existing diversity. It ■ is .possible to draw' a | chemical analogy here. Work on the : radioactive elements has shown that I the chemical elements are not abso--1 lutely immutable bodies. An atom of ; one element under certain conditions changes into an atom of another ele--1 ment. But the great variety of maI terial substances arousd us is not duo i to this instability of the elements. It is due to the enormous numbers of | different combinations between a com- ; paratively few highly stable elements. | Tf this view be correct, the l role of | selection appears to be a more limited I one than that conceived by thS follow- ; ers of Danvin. All that selection can do. is to isolate a certain combination of factors out of those present in _ a mixed population. Having done this, it is powerless to produce further advance unless'a mutation of a factor should take, place, and so far as experimental work can show us such mutations arise quite without reference to the needs of the organism, | \ Mankind still in the Dark. 1 Even .the limited scope sef to the action of selection under this scheme leaves it a very powerful factor, dn the British people, there is certain y

I’ a sufficiently heterogeneous assortment of hereditary factors to allow of the production, »hy selection alone, of a race with an average height of 7ft., or of 4ft., or of a race with the average intelligence of an imbecile, or of what to-day constitutes an exceptionally clever man. Still, to the evolutionist the great problem is not the manipulation of existing material, but the origin of iiew material. In spite of much laborious expenditure of talent and labor it must be confessed that we are still in the dark as to the how and why real novelties come into being. The study of mutation, where at least we scent to have new hereditary factors arising before us, has not helped us at all. to understand the stages by which complexly adapted organs, such eye, let alone, the organism as a whole, has been evolved.

After 05 years, then, Darwin’s mechanistic explanation of evolution by the natural selection of random variations still remains a subject of lively debate. How far the explanation is efficacious is a question to which, experimental work gives no certain answer. This conclusion may be disappointing, but is at least stimulating to further research.