Life and Death, Heredity and Evolution 



visible difference made by mating, and it is the same sort of 

 result that is produced by mating in higher organisms. In 

 the latter in consequence of mating, offspring are produced 

 which are more alike than are individuals taken at random; 

 this is likewise what happens in Paramecium. 



In higher organisms we say that this result is an example 

 of heredity. As we are accustomed to think of it, the off- 

 spring in a family inherit from both their parents ; they 

 resemble both the parents ; and this appeals to us as a reason 

 why they should resemble each other. Now, whether the off- 

 spring of the two members of a pair of Paramecia resemble 

 also their parents has not been directly shown; it is a dif- 

 ficult matter to get at; what we know is that they do 

 show a marked resemblance to each other. But this matter 

 of resemblance between the external features of parent and 

 offspring is in reality a totally inadequate basis for a con- 

 ception of heredity. In the study of heredity in higher 

 organisms, we often discover that the offspring inherit char- 

 acteristics from the parents which the parents do not show, 

 as when rabbits with white hair are born from parents 

 with brown hair; or when two white fowls produce black 

 chicks. In such cases the black color of the chicks is in- 

 herited from the white parents just as truly and in just the 

 same way as occurs when black parents produce black 

 chicks. The only consistent meaning we can give to heredity 

 is this : heredity is the appearance of peculiarities in the off- 

 spring that are due to the peculiarities of the germinal 

 material they obtained from their parents. And we know 

 that white fowls do frequently transmit to their offspring 

 germ cells of such a character that the offspring must be 

 black; such cases are recognized as clear examples of Men- 

 delian inheritance. By biparental inheritance we mean mere- 

 ly this: the peculiarities of the given individual, taken as a 



