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Updated: May 9, 2025
We have said that the following out of the properties exhibited by physiological species would lead us into difficulties, and at this point they begin to be obvious; for if, as the result of spontaneous variation and of selective breeding, the progeny of a common stock may become separated into groups distinguished from one another by constant, not sexual, morphological characters, it is clear that the physiological definition of species is likely to clash with the morphological definition.
Whatever may be the character of any infusion, or to whatever incidence of conditions it may be subjected, it will produce some form of life; not because it contains this or that morphological cell, destructible at a temperature of 100A deg.
They are primordial manifestations of life, and such as would have made their appearance in any corresponding latitude of the southern hemisphere, under the same favoring conditions. And this is true of all living organisms from the lowest morphological cell, in the ichthyologic world, to the highest and lordliest conifer that grows.
If we consider, in fact, that by far the largest proportion of recorded existing species are known only by the study of their skins, or bones, or other lifeless exuvia; that we are acquainted with none, or next to none, of their physiological peculiarities, beyond those which can be deduced from their structure, or are open to cursory observation; and that we cannot hope to learn more of any of those extinct forms of life which now constitute no inconsiderable proportion of the known Flora and Fauna of the world: it is obvious that the definitions of these species can be only of a purely structural, or morphological, character.
He showed convincingly that the ideas of hand and foot had been wrongly defined, and had been improperly based on physiological instead of morphological grounds.
It is important to realize the continuous, self-contained morphological development of English and the very modest extent to which its fundamental build has been affected by influences from without.
We also know that words may be diffused no less freely than cultural elements, that sounds also may be "borrowed," and that even morphological elements may be taken over. We may go further and recognize that certain languages have, in all probability, taken on structural features owing to the suggestive influence of neighboring languages.
They are also divisible into groups of individuals, which breed freely together, tending to reproduce their like, and are physiological species. Normally resembling their parents, the offspring of members of these species are still liable to vary; and the variation may be perpetuated by selection, as a race, which race, in many cases, presents all the characteristics of a morphological species.
Even new-born infants of our own race can grasp very strongly with the great toe, and hold a spoon with it as firmly as with the hand. Hence the physiological distinction between hand and foot can neither be pressed very far, nor has it a scientific basis. We must look to morphological characters.
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