Note on the Skin-Colour of the Crosses Between Negro and White

Note on the Skin-Colour of the Crosses Between Negro and White

Biometrika
Volume 6, Number 4 (March 1909)
pages 348-353
DOI: 10.1093/biomet/6.4.348

Karl Pearson (1857-1936), F.R.S.

Those who feel compelled at present to hold their final judgment with regard to Mendelism in suspense, who do not think the statistical proof of its generality by any means yet complete, and who still question on logical grounds many of the statements made with regard to it, have nevertheless been ready to emphasise the paramount service of Mendel in drawing attention to the great factor of segregation in many inheritance problems. This admission can be made without overlooking the facts—too often disregarded—that segregation is not a universal principle, that it is, where it does occur, often incomplete, and that even where it occurs and is more or less complete it does not necessarily follow the simple Mendelian ratios. The theory of the “pure gamete,” the “unit character” and the  “allelomorph” may have aided, suggested and controlled much experimental work on inheritance, but this theory has undoubtedly been pushed—chiefly by young and enthusiastic disciples of Mendelism, who thought that at last a formula of heredity requiring no mathematical knowledge had been discovered—far beyond the limits of actual experimental work, or in some cases beyond the inferences allowable from the data actually observed. The public has been dosed by the general Mendelian practitioner with:

(DR) x (DR) = (DD) + 2(DR) + (RR)

and told that it solved all difficulties. But the higher consultants know that at the very best many complications arise, that even in segregation transitional forms occur occasionally or even frequently, and that “unit characters” are not independent but often highly correlated. They are also fully conscious that much straining of the theory of probability often is needed to make the ratios fit a simple Mendelian formula. The reason for these prefatory remarks lies in the fact that some time ago it was asserted by an ardent Mendelian that skin colour in crosses between dark and light skinned races would probably be found to obey Mendelian principles.   It had been hitherto almost universally accepted that skin colour did…

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