Evolution: Its nature, its evidence, and its relation to religious thought

by Joseph LeConte

Application of these principles to some questions of the day:

I. Evolution, as a law of derivation of organic forms from previous forms by descent with modifications, as already shown, is as certain as the law of gravitation. This question has passed beyond the realm of doubtful discussion; but the causes, the factors, the details of the process of evolution are still under discussion. Both Darwin and Spencer, the two great founders of the theory of evolution in its modern form, acknowledge and insist on at least four factors, viz., the two Lamarckian and the two distinctively Darwinian. The only difference between them is in the relative importance of the two sets: Spencer regarding the former and Darwin the latter as the more potent. But in these latest times there has arisen a class of biologists, including some of highest rank, such as Wallace, Weismann, and Lankester, who out-Darwin Darwin himself in their exaltation of the most distinctive Darwinian factor, viz., natural selection. They try to show that natural selection is the sole and sufficient cause of evolution; that changes in the individual, whether as the effect of the environment or by use and disuse of organs, are not inherited at all; that Lamarck was wholly wrong; that Darwin (in connection with Wallace) was the sole founder of the true theory of evolution; and, finally, that Darwin himself was wrong only in making any terms whatever with Lamarck. This view has been called Neo-Darwinism.

Perhaps the reasons for this view have been most strongly put by Weismann, and are based partly on experiments, but mainly on his ingenious and now celebrated theory of the immortality of germ-plasm. The animal body consists of two kinds of cells wholly different in function—somatic cells and germ-cells, including in this last the sexual elements both male and female. Somatic cells are specially modified for the various functions of the body; germ-cells are wholly unmodified. The somatic cells are for the conservation of the individual life, the germ-cells for the conservation of the species. In the development of the egg the germ-cell multiplies itself into a cell-aggregate, and then most of the resulting multitude of cells are modified in various ways to form the tissues and organs of the body—somatic cells; but a few are reserved and put aside in an unmodified form in the sexual organs as germ-cells, to again produce ova which again divide into somatic and germ-cells, and so on indefinitely. Now, according to Weismann, inheritance is only through germ-cells, while the environment affects only the somatic cells. Therefore changes produced by the environment can not be inherited. Sexual modes of generation were introduced for the purpose of producing variability in progeny, and thus furnishing material for natural selection, as this was the only means of evolutionary advance. Weismann made many experiments on animals, especially by mutilation, to show that somatic changes are not inherited.

A full discussion of this question would be unsuitable in a work like this. We will therefore content ourselves with making three brief remarks:

a. If the views presented in the early part of this chapter are true, then the Lamarckian factors must be true factors, because there was a time when there were no others. They were therefore necessary, at least to start the process, even if no longer necessary at present.

b. But if these factors were ever operative, they must be so still, though possibly in a subordinate degree. A lower factor is not abolished, but only becomes subordinate to a higher when the latter is introduced. Thus it may well be that Lamarckian factors are comparatively feeble at the present time and among living species, especially of the higher animals, and yet not absent altogether. In the earliest stages of evolution there was a complete identification of germ-cells and somatic cells—of the individual with the species. In such cases, of course, any effect of the environment must be inherited and increased from generation to generation. But the differentiation of the germ and somatic cells was not all at once, nor is their sympathetic relation completely severed. It was a gradual process, and therefore the effect of the environment on the germ-cells through the somatic cells continued, though in decreasing degree, and still continues. The differentiation in the higher animals is now so complete that germ-cells are probably not at all affected by changes in somatic cells, unless these changes are long continued in the same direction, and are not antagonized by natural selection.

c. It is a general principle of evolution that the law of the whole is repeated with modifications in the part. This is a necessary consequence of the unity of Nature. We ought to expect, therefore, and do find, that the order of the use of the factors of evolution is the same in the evolution of the organic kingdom, in the evolution of each species, and in the evolution of each individual. In all these the physical factors are at first powerfully operative; these become subordinate to organic factors, and these, in their turn, to psychical and rational factors. Therefore, as the individual in its early stages—i. e., in embryo and infancy—is peculiarly plastic under the influence of the physical environment, and afterward becomes more and more independent of these; so a species when first formed is more plastic under the influences of Lamarckian factors, and afterward becomes more rigid to the same. And so also the organic kingdom was at first more plastic under Lamarckian factors, and has become less so in the present species, especially in the higher animals. The principal reason of this, as we have already seen, is the increasing differentiation of germ and somatic cells, and the removal of the former to the interior, where they are more and more protected from external influence.

II. Some evolutionists—the materialistic—insist on making human evolution identical in all respects with organic evolution. This, we have shown, is not true. The very least that can be said is that a new and far more potent factor is introduced with man, which modifies greatly the process. But we may claim much more, viz., that evolution is here on a different and higher plane. The factors of organic evolution are, indeed, still present, and condition the whole process; but they are not left to be used by Nature alone. On the contrary, they are used in a new way and for higher purposes—by reason.

But by a revulsion from the materialistic extreme some have gone to the opposite extreme. They would place human progress and organic evolution in violent antagonism, as if subject to entirely different and even opposite laws; but we have also shown that, although the distinctive human factor is indeed dominant, yet it is underlaid and conditioned by all the lower factors; that these lower factors are still necessary as the agents used by reason.

III. We have already given the views of Weismann and Wallace, and some reasons for not accepting them; but there is one important aspect not yet touched. There are some logical consequences of these views when applied to human evolution which seem to us nothing less than a reductio ad absurdum. This brings into view still another contrast between organic evolution and human progress.