APPLICATIONS OF PRINCIPLES OF HEREDITY 455 



it would be necessary to go back' several centuries ; and such 

 records were not kept in so remote a period. With annual 

 plants and many animals it is possible to get a generation each 

 year, and with some organisms several generations in a year. 



The number of offspring in human matings is comparatively 

 small, so that it is never possible to get even an approxi- 

 mation of all the character combinations in any one family. 

 Experiments are, of course, out of the question. 



Finally, what we call the human race is really a mixture of 

 many distinct types or combinations of characters, and these 

 are so thoroughly mixed up that we never find a pure race 

 of human beings at the present time. 



Nevertheless, by comparing such family records as are avail- 

 able with the behavior of various characters in the pedigrees 

 of plants and animals, it has been possible to show that 

 many human characters follow the same hereditary principles 

 of dominance, segregation, and recombination. 



The diagrams in Fig. 243 show the course of certain 

 characters in several carefully studied cases. 



The following table gives a list of human characters that 

 are known to be dominant or recessive : 



HEREDITY IN MAN 



DOMINANT CHARACTER 



RECESSIVE CHARACTER 



Curly hair 



Dark hair 



Beaded hair 



Brown eyes 



Normal pigmentation 



Hapsburg lip 



Normal muscular tone 



Nervous temperament 



Fused ringers or toes 



Supernumerary digits 



Broad fingers (lacking one joint) 



Limb dwarfing 



Normal growth 



Straight hair 



Light ; red 



Even hair 



Blue eyes 



Albinism 



Normal lip 



Low muscular tone 



Phlegmatic temperament 



Normal digits 



Normal number 



Normal length 



Normal proportion 



General dwarfing 



