14 



SOCIAL EVOLUTION 



mice alone. Tliis is because tliey are piire*recessives. 

 But some of the normal mice produce only normal mice ; 

 these are pure dominants, while others of the normal 

 mice produce normal and waltzing mice in the proportion 

 of three normal to one waltzing- mice; these are impure 



NORMAL MOUSE WALTZING MOUSE 



Figure 5. .MemU-lian Inheritance in Mice. 



dominants. This law does not mean that if there were 

 only four offspring of a mouse in the first filial generation 

 Fi, one would be normal and would breed only normal, 

 two would be normal but would breed both normal and 

 waltzing mice, and one would be waltzing and would 

 breed only waltzing mice. It might, of course, happen 

 this way. What it means is, that on the average, if one 

 were to study a great number of matings of normal and 

 waltzing mice, the offspring would possess the waltzing 

 trait in the proyjortion indicated. It does not enable one 

 to make a dogmatic prediction about a small group of 

 brother and sister mice. 



Figure 6 shows the inheritance of color in which one 



