316 



Prof. Karl Pearson. 



" Data for the Problem of Evolution in Man. IV. Note on the 

 Effect of Fertility depending on Homogamy." By Karl 

 Pearson, F.R.S., University College, London. Received 

 March 12 —Read March 29, 1900. 



1 . In a paper recently contributed to the ' Proceedings of the Royal 

 Society,' " Data for the Problem of Evolution in Man. III. On the 

 Magnitude of Certain Coefficients of Correlation in Man,"* &c., I dealt 

 with the problem of the possible dependence of fertility on homogamy, 

 and I used the following words (p. 29) : — 



" When any form of life breaks up into two groups under the in- 

 fluence of natural selection, what is to prevent them intercrossing and 

 so destroying the differentiation at each fresh reproductive stage 1 " 



The answer I suggested was twofold — (i) homogamy, which I ca>n 

 demonstrate to actually exist in the case of man, and (ii) a possible 

 dependence of fertility on homogamy, which would render the cross 

 unions relatively sterile. Either (i) or (ii) would be effective, but (ii) 

 would have the advantage that it does not presuppose assortative 

 mating ; we could have a permanent differentiation even with random 

 mating. In writing the above sentence, I had two further points in 

 mind : (a) that reproductive selection, while quite capable of producing 

 an evolution, a progressive change in a species, could not by itself 

 differentiate a species into tw^o sub-groups, and (b) that no correlation 

 of homogamy with fertility could possibly differentiate a species, how- 

 ever much it might cause the species to progressively change as a 

 whole. My view was that a correlation of homogamy with fertility, 

 together with natural selection, could produce a permanent differentia- 

 tion of species, but that neither alone could be effectual. It was from 

 this standpoint that I concluded my paper with the words : — 



"I can conceive no more valuable investigation than a series of 

 experiments or measurements directed to ascertaining whether homo- 

 gamy is or is not correlated with fertility " (p. 32). 



In writing these words I overlooked a very admirable piece of work 

 by Mr. H. M. Vernon, M.A., published in our own ' Transactions,' on 

 " The Relations between the Hybrid and Parent Forms of Echinoid 

 Larvae."! Had I been acquainted with this memoir, I should certainly 

 have referred to it. In drawing my attention to it, Mr. Vernon has 

 also referred me to two papers by himself in ' Natural Science,' on 

 what he terms "Reproductive Divergence."! While welcoming 

 heartily Mr. Vernon's facts in the paper on " Echinoid Larvae," bearing 



* ' Proc. Eoy. Soc.,' vol. 66, p. 28. 



t ' Phil. Trans.,' B, vol. 190, p. 465—529. 



I Yol. 11, pp. 181—189 and pp. 404—407. 



