Page:Popular Science Monthly Volume 76.djvu/319

Rh such modifications as are known to occur within the individual life at any time from conception to death or within a single generation. This will throw out of the question a hoard of cases where it is not quite clear whether the observed changes are the result of direct modification, in the true restricted sense, or are perhaps due in part to accumulated influences acting through several generations.

Confining ourselves then to a discussion of modification in the strict sense of the term, let us briefly survey the conclusions of experimental zoology, embryology and botany, and also experiments on regeneration, to see what lesson may be learned from the results of all this painstaking work. It will be of course impossible to treat of more than a fraction of the multitudinous results which have already been handed in as contributions to this young and rapidly growing branch of knowledge—experimental biology; but I believe that even a superficial survey will suffice to bring out my general contention.

The fact that ordinary differences in human environment, as shown in the history of royalty, appeared to alter the innate character and capacity for achievement but little, together with the fact that experimentally a great deal in the way of modification could be produced in the domains of zoology and botany, led me to suppose that there must be some inherent biological differences rendering tissues low in the organic scale especially susceptible to the molding of external influences.

This idea I advanced as an hypothesis in 1906 in the following words:

In 1908 I expressed the same idea in the following passage:

It is to offer the proof for this generalization that I now propose a survey of the whole question.