Animal life as affected by the natural conditions of existence
It was Jaeger who once said—but I forget where—that enough had been done in the way of philosophising by Darwinists, and that the task that now lay before us was to apply the test of exact investigation to the hypotheses we had laid down. ' I have long agreed, but it is in fact a thing much easier said than done.
It is infinitely easy to form a fanciful idea as to how this or that fact may be hypothetically explained, and very little trouble is needed to imagine some process by which hypothetical fundamental causes—equally fanciful—may have led to the result which has been actually observed. But when we try to prove by experiment that this imaginary process of development is indeed the true and inevitable one, much time and laborious research are indispensable, or we find ourselves wrecked on insurmountable difficulties.
Nevertheless, the step must be taken. The popular cant about ‘ Biogenetic principles and the falsification of Ontogenesis—the laws of inheritance at corresponding periods of life, or the correlation of organs—Ontogeny and Phylogeny—variability and heredity ’—is put out of court as useless, for these are merely axiomatic expressions for a sum of identical or correlative phenomena of which the essential nature is in no way revealed by them. They all still await an intrinsic explanation.
It appears to me that of all the properties of the animal organism, Variability is that which may first and most easily be traced by exact investigation to its efficient causes; and, as it is beyond a doubt the subject around which at the present moment the strife of opinions is most violent, it is that which will be most likely to repay the trouble of closer research.
I have endeavoured to facilitate this task, so far as in me lies, by here presenting a general view of those facts and hypotheses which bear upon the subject and are either of universal significance or, from my point of view, appear to offer favourable subjects for experimental treatment. This list, however, makes no pretension to completeness. If only it should give an impulse to research, on however small a scale, so long as it is systematically conducted and thoroughly carried through—if only it should contribute to extending my own convictions as to the uselessness of casual and disconnected observations, I shall have attained my end.
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