52 ANIMAL LIFE AND HUMAN PROGRESS 



(1) What have all these experiments on fruit-flies and peas 

 and other animals and plants got to do with man ? 



(2) The characters enumerated and the factors that give 

 rise to them are all small structural characters, and where is 

 the evidence that mental endowments are subject to these 

 laws ? 



The answer to the first criticism is that a considerable 

 number of characters in man have been shown to follow 

 Mendelian laws. It is not possible, of course, to make exact 

 breeding experiments with man, but by carefully collecting 

 and recording the pedigrees of families affected by some 

 peculiarity, it has been shown that colour-blindness, night- 

 blindness, brachydactyly and a number of other characters 

 are transmitted in accordance with these laws, some, such as 

 colour-blindness, affording curious examples of sex-linked 

 inheritance. 



As to the second criticism, it is notorious that feeble- 

 mindedness is inherited in man, and that is a mental character, 

 if not exactly an endowment. There is another interesting 

 fact which I have frequently witnessed and can personally 

 vouch for the truth of. Many experiments have been made 

 with mice. A common cross has been that between an albino 

 mouse and a Japanese waltzing mouse. Both of these have 

 red eyes, and in addition to other characters are peculiar for 

 their tameness. They show no fear on being handled and do 

 not try to escape. 



When crossed together these two races give a hybrid in Fl 

 which is very like but somewhat paler than the common grey 

 (" agouti ") house-mouse and has black eyes. When these 

 hybrids are interbred a variety of forms are produced, among 

 which there is always a certain proportion of grey mice indis- 

 tinguishable from the common house-mouse. These greys are 

 invariably ivild, will not bear handling and are continually 

 eating through and escaping from their cages. Tameness and 

 wildness are mental characteristics. There is in this case a 

 curious linkage between the external appearance and the 

 mental habit, and it illustrates the statement of Morgan that a 

 " factor " may control more than one character in the indi- 



