286 



The Journal of Heredity 



cial, projects, and such records of 

 human breeding as are available, 

 would probably be the most direct 

 method of approaching an understand- 

 ing of the laws governing the inherit- 

 ance of characters in domesticated 

 artimals and man. Thousands of 

 grouse locusts of strikingly contrast- 

 ing characters and for ten or twelve 

 succeeding generations may be bred 

 with the facilities, expense and time re- 

 quired in breeding one, or two, of the 

 higher domesticated mammals. Just 

 as the bulk of the facts of surgery 

 and medicine has been gained largely 

 through experimentation on lower 

 animals, so it appears that an ap- 

 proach to an understanding of the 

 laws of inheritance as applied to 

 domesticated animals and man may be 

 made, with proper supplementation, 

 largely through the utilization in ex- 

 perimentation of such rapidly breed- 

 ing and comparatively simple forms 

 as fruit flies, grouse locusts and lower 

 mammals. 



Th breeding pens and cages of the 

 geneticists are instruments analogous 

 to the test tubes and mortars of the 

 chemist. This is not overdrawn, for 

 in the breeding of fruit flies millions 

 of reactions of the factors of heredity 

 have been recorded. In one experi- 

 ment with grasshoppers we have 

 checked and recorded more than 350,- 

 000 reactions among contrasting char- 

 acters. Many other groups of animals 

 and plants have been used in the same 

 way. It is a fact that thousands of 

 the factors which manifest themselves 

 in the characters of animals and ])lants 

 are every day being manipulated with 

 the same precision and method as are 

 a];plicable to the operations of the 

 chemical elements. Even the same 

 difiiculties of errors resulting from 

 contaminations, failure in the identifi- 

 cation of end results, etc., have to be 

 met. The precision with which gene- 

 tic factors react towards each other 

 has called for the establishment of a 

 s])ecial branch or sub-branch of 

 mathematics with which to deal with 

 the subject ; so that now when one 



contemplates entering the field of 

 genetics he finds a knowledge of cer- 

 tain lines of mathematics a prerequis- 

 ite. 



There are about 140 characteristics 

 of man known to be inherited. It has 

 been ascertained that a large propor- 

 tion of these are inherited according 

 to Mendelian expectation, and none 

 have been proved to be inherited 

 otherwise. Color blindness, a chart 

 for which I have shown (see Figure 

 14), is one of the conspicuous exam- 

 ples of those which have been thor- 

 oughly worked out. Skin color ; the 

 hair, whether straight, curly, kinkey, 

 golden, red or black ; tallness ; dwarf- 

 ness ; thinness ; fatness ; bodily mal- 

 formation ; susceptibilities ; immunities ; 

 inebrity ; sobriety ; sex immorality ; 

 criminality ; inbecility ; intellectuality ; 

 ambition ; vigor ; longevity ; altruism 

 and religious fervor are a few of the 

 constantly increasing number of such 

 herital)le characters that are coming 

 into recognition. 



We have time to consider only one 

 characteristic of man, besides the case 

 of color-blindness already illustrated. 

 I shall take the case of skin color of 

 the negro stvidied especially by the 

 Davenports. After extensive studies 

 they concluded that there are two fac- 

 tors for black pigmentation in the 

 full-blooded negro of the West coast 

 of Africa. Briefly this means that 

 the mulatto first generation offspring 

 from pure black crossed with pure 

 whites, when inbred, should produce 

 one pure white and one pure black in 

 every sixteen of the second generation 

 offspring. (See Figure 15.) Now, this 

 refers to color only. According to 

 the laws of the shuflling of factors, 

 the pure white individual in color may 

 have more of the other negroid char- 

 acteristics, such as flat nose, thick 

 lips, curly hair, mental traits, than the 

 pure black individual of the same par- 

 entage and vice versa. To secure a 

 pure black, with all other negroid 

 characters, or a pure white, with all 

 other Caucasian traits from mulattos 

 would be a very rare occurrence in- 



