Darwinism to-day : a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxiliary and alternative theories of species-forming / by Vernon L. Kellogg.

  • Vernon Lyman Kellogg
Date:
1907
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Licence: In copyright

Credit: Darwinism to-day : a discussion of present-day scientific criticism of the Darwinian selection theories, together with a brief account of the principal other proposed auxiliary and alternative theories of species-forming / by Vernon L. Kellogg. Source: Wellcome Collection.

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    carrying over? Has natural selection’s claimed capacity to effect species change, unseen by observer, untested by exper- imenter, any better or even other proof of actuality than that just offered on behalf of species modification as a direct result of the stimulus of varying environment and func- tional exercise? I cannot see that it has. And this kind of argument, based half on observed facts and half on deduction, may be extended even farther on mi ,. , behalf of the theory that species change is the The same kind J of proof for non- direct reaction to environmental conditions. adaptive change. jror t]lere are many ontogenetic variations pro- duced directly in response to environment that are not plainly adaptive; many, indeed, between which and the environmental conditions that produce them no reasonable relation is apparent; no relation, that is, that would be ex- actly expected or could be foretold until empirically deter- mined. In other words, many apparently non-significant ontogenetic differences or variations appear as direct result of environmental influence or stimulus. For example, indi- viduals of certain species of the Crustacean phyllopod genus Artemia show marked structural differences when grown in salt water of varying density. These differences are in the size and shape of the plate-like lateral gills, the seg- mentation of the post-abdomen, the length of the caudal flaps (telson) and the hairiness of these flaps. The size of the whole body is also affected, individuals developing in water of higher density being markedly smaller than those which have been grown in less dense water. Now of all these differences only two seem to have what I call a rea- sonable relation to the environmental differences. The in- creased proportional size of the gills shown by the Artemias grown in denser water appears to be a regulatory change connected with the smaller amount of oxygen in the water,, and the decreased size of the body may similarly be con- ceived by some to be an expected concomitant of the.