CHAPTER XV 



MAN 



Though the interest attaching to heredity in man is 

 more widespread than in other animals, it is far more 

 difficult to obtain evidence that is both complete and ac- 

 curate. The species is one in which the differentiating 

 characters separating individual from individual are very 

 numerous, while the number of the offspring is compara- 

 tively few, and the generations are far between. For 

 these reasons, even if it were possible, direct experimen- 

 tal work with man would be likely to prove both tedious 

 and expensive. There is, however, another method be- 

 sides the direct one from which something can be learned. 

 This consists in collecting all the evidence possible, ar- 

 ranging it in the form of pedigrees, and comparing it with 

 standard cases already worked out in animals and plants. 

 In this way it has been possible to demonstrate in man 

 the existence of several characters showing simple Men- 

 delian inheritance. As few besides medical men have 

 hitherto been concerned practically with heredity, such 

 records as exist are, for the most part, records of deform- 

 ity or of disease. So it happens that most of the pedi- 



