270 Evolution and Adaptation 
what is quantitively the rate at which it is working and has 
worked.” This statement expresses no more than Pearson’s 
conviction that the process of evolution has taken place by 
means of selection. He ignores other possibilities, which if 
established may put the whole question in a very different 
light. 
HEREDITY AND CONTINUOUS VARIATION 
It has been to a certain extent assumed in the preceding 
pages that both parents are alike, or, if different, that they 
have an equal influence on the offspring. This may be true 
in many cases for certain characteristics. Thus a son from 
a tall father and a short mother may be intermediate in 
height, or if the father is white and. the mother black, the 
children are mulattoes. But other characters rarely or never 
blend. In such cases the offspring is more like one or the 
other parent, in which case the inheritance is said to be 
exclusive. Thus if one parent has blue eyes and the other 
black, some of the children may have black eyes and others 
blue. There are also cases of particular inheritance where 
there may be patches of color, some like the color of one 
parent, some like that of the other parent. The latter two 
- kinds of inheritance will be more especially considered in the 
subsequent part of this chapter; for the present we are here 
chiefly concerned with blended characters. 
How much in such cases does each parent contribute to the 
offspring ? This has been expressed by Galton in his law of 
ancestral heredity. This law takes into account not only the 
two parents, but also the four grandparents, and the eight 
great-grandparents, etc. There will be 1024 in the tenth 
generation. These 1024 individuals may be taken as a fair 
sample of the general population, provided there has not been 
much interbreeding. Are we then to look upon the individ- 
ual as the fused or blended product of the population a few 
generations back? If this were true, should we not expect 
