116 NATURAL INHERITANCE. [chap. 



In each generation, individuals are found to be tall 

 and short, heavy and light, strong and weak, dark 

 and pale ; and the proportions of those who present 

 these several characteristics in their various degrees, 

 tend to be constant. The records of geological history 

 afford striking evidences of this statistical similarity. 

 Fossil remains of plants and animals may be dug out of 

 strata at such different levels^ that thousands of genera- 

 tions must have intervened between the periods at which 

 they lived ; yet in large samples of such fossils we may 

 seek in vain for peculiarities that distinguish one 

 generation from another, the different sizes, marks, and 

 variations of every kind, occurring with equal frequency 

 in all. 



If any are inclined to reply that there is no wonder 

 in the matter, because each individual tends to leave his 

 like behind him, and therefore each generation must, as 

 a matter of course, resemble the one preceding, the 

 patent fact of Regression shows that they utterly 

 misunderstand the case. 



We have now reached a stage at which it has 

 become possible to discuss the problem with some 

 exactness, and I will do so by giving mathematical 

 expression to what actually took place in the Statures 

 of that sample of our Population whose life-histories 

 are recorded in the R.F.F. data. 



The Males and Females in Generation I. whose M has 

 the value of P (viz., 685- inches), and whose Q is 1*7 

 inch, were found to group themselves as it were at 

 random, into couples, and then to form a system of 



