The power of environment : nurture versus nature / editor: Henry Smith Williams, M.D., LL.D.

Date:
[1914]
Catalogue details

Licence: Public Domain Mark

Credit: The power of environment : nurture versus nature / editor: Henry Smith Williams, M.D., LL.D. Source: Wellcome Collection.

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    average diversity of tendencies, and (2) an ab- normal instability of tendencies, due to the accent- uation of certain groups. And here practical ob- servation fully sustains theory. It is by the appli- cation of these principles that all the specialized races of domestic animals have been so rapidly developed. The influence of Mendelian heredity might be described, for the present purpose, in closely similar terms. Through this influence, as we have seen, the factors for various qualities in the organ- ism may be so distributed that some of the off- spring are entirely without certain of the tenden- cies of their parents. Reverting again to our familiar illustration, it will be recalled that the offspring of blue-eyed parents all have blue eyes, with no tendency to blackness, even though one of their grandparents may have had black eyes. Stated in Mendelian terms, this implies that blue eyes are recessive; it being observed that re- cessive qualities, once they reappear, breed true. On the other hand, a person with blue eyes may have a brother or sister with black eyes, representing a strain in which there is no tendency whatever to blue eyes. So two different strains, as regards eye color, may be developed from indi- viduals of the same fraternity. And what is true of eye color is true also of a [20]
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