Page:The Scientific Monthly vol. 3.djvu/509

 ORIGIN AND EVOLUTION OF LIFE

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��reactions and interactions with each other and with the environment are heritable by the chromatin. This idea was originally suggested by the accurate observation of early naturalists and anatomists that bodily function not only controls form but is generally adaptive or purposive in its effects. According to this Lamarck-Spencer-Cope explanation a change of environment^ of habit and of function should always be antecedent to changes of form in succeeding generations; moreover, if this explanation were the true one, successive changes in evolutionary series would be like growth, they would be observed to follow the direct lines of individual action, reaction and interaction, the young would be increasingly similar to the adults of antecedent generations, which is frequently the case but unfortunately for the Lamarckian explanation is not invariably the case.

The opposed explanation, the Darwinian, as restated by Weismann and De Yries, is that the beginning of new form and function is to be sought in the germ cells or chromatin. This is based upon the direct anti-Lamarckian view that the ac- tions, reactions and interactions which cause certain bodily organs to origioate, to develop, or to de- generate, to exhibit momentum or inertia in development, are not in- herited and do not give rise to corre- sponding sets of predispositions in the chromatin. According to this explanation all predispositions to new form and function not only begin in the germ cells but are more or less lawless or experimen- tal, they are constantly being tested or tried out by bodily experience, habits and functions. Technically stated they are fortuitous variations followed by selection of the fittest variations. Thus Darwin's disciple, Poulton, also De Vries, who has merely restated in his law of "muta- tion '* Darwin's original principle of 1859, and Bateson, the most radical thinker of the three, hold the opin- ion that there is no adaptive law observed in variation but that the chro- matin is continuously experimenting and that from these experiments selection guides the organism into adaptive and purposive lines.

Neither the Lamarckian nor the Darwinian explanation accords

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a. The peculiar slgnlflcance of ver- tebrate chromatin is its stability in combination with incessant plasticity and adaptability to varying environ- mental conditions and new forms of bodily action.

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