Febeuabt 4, 1910] 



SCIENCE 



185 



raise up, in some part of the world, a race 

 superior to the stock from which it sprang. 



Natural selection has been suggested as 

 such a cause. Life in the tropics, it has 

 been said, is too easy to demand much in- 

 ventiveness or forethought, but a migration 

 to colder regions, where the banana does 

 not grow, would make mental activity im- 

 perative, and select those individuals who 

 were able to respond, so producing a su- 

 perior race. There is a difficulty here, since 

 we should expect natural selection to begin 

 by lopping off the most poorly endowed 

 fraction of the population, with the result, 

 finally, that the lower range of intelligence 

 should disappear from the higher races. 

 The lowest grade of intelligence in Europe 

 should accordingly be higher than the low- 

 est grade in Africa. But this is probably 

 not the case; the range of intelligence 

 reaches as low in one as in the other. The 

 distributions of intelligence in the two also 

 overlap to quite an extent. Extensive ex- 

 periment has shown that Africans can 

 maintain existence in the temperate zone. 



Sexual selection, or, more properly, 

 mating customs, furnish a more promising 

 factor. If a tendency could be detected in 

 any population for the most intelligent 

 members to mate with each other, the result 

 would be, not indeed a raising of the av- 

 erage intelligence, since the less intelligent 

 would also mate with each other, but an 

 increase of the variability, and greater 

 chance of the birth of very superior indi- 

 viduals. A caste system might operate in 

 this way, since the founders of aristocratic 

 families probably won admission to the 

 caste partly by virtue of intelligence, and 

 their descendants would tend, by heredity, 

 to exceed the average intelligence of the 

 population. Marriage confined to the caste 

 would thus tend to mate superior individ- 

 uals with each other, and might, in the 

 course of generations, raise the upper limit 



of intelligence. Customs of mating within 

 one's rank obtain among the aristocracy 

 and royalty of Europe, and may have been 

 a factor in increasing the number of su- 

 perior intelligences. But too much can not 

 be attributed to this factor, since the selec- 

 tion has been by classes, and not by indi- 

 viduals. Royalty, while marrying within 

 its rank, has not usually chosen the most 

 gifted individual available. Its selection 

 has been relatively inefficient from the 

 standpoint of royal eugenics. Certainly 

 the upper reach of European intelligence 

 has not been the' result of breeding by 

 castes ; for, though royalty has indeed pro- 

 duced a disproportionate number of high 

 intelligences, equally able individuals have, 

 as a matter of fact, risen from humble 

 birth. Moreover, marriage in all parts of 

 the world is largely governed by considera- 

 tions of family standing and wealth, so that 

 the same sort of influence toward variabil- 

 ity is everywhere operative. The dead 

 level of intelligence, which is sometimes 

 supposed to obtain among backward races, 

 is not borne out by psychological tests, 

 since individual differences are abundantly 

 found among all races, and, indeed, the 

 variability of different groups seems, from 

 these tests, to be about on a par. 



Selection by migration is also to be con- 

 sidered. When individuals leave their 

 group and go to a new country, it would 

 seem that those who emigrate must differ, 

 on the average, from those who remain be- 

 hind. An adventurous and enterprising 

 spirit, perhaps, would be characteristic of 

 the emigrants, and so of the new people 

 which they helped to form. On the other 

 hand, the ne'er-do-well and the criminal 

 might also be induced to emigrate. The 

 selective influence of migration would not 

 be all in one direction, and the net result 

 could not easily be predicted. Since we 

 are now witnessing, though little compre- 



