SOCIAL EVOLUTION 



VAEIATION AND HEREDITY 



WE know that among both animals and plants the off- 

 spring tend to resemble their parents. The young of a 

 dog is always a dog and never a cat. Rabbits do not give 

 birth to guinea pigs. Roses will not grow from potato 

 seeds. Each kind of animal and plant breeds true as the 

 biologist says. But this principle has not always been 

 recognized. The Greeks believed that certain animals 

 originated from plants. In the Middle Ages it was be- 

 lieved that the goose-barnacle (a kind of crustacean) 

 transforms into a barnacle-goose. But we have accumu- 

 lated sufficient experience of nature in the centuries that 

 have passed since Medieval times to affirm with confi- 

 dence that animals and plants do breed true. 



It is a fact perfectly familiar to breeders that the 

 young usually resemble the particular individuals from 

 which they have sprung. Therefore we can say that not 

 only do plants and animals, when they reproduce, give 

 rise to young which belong to the same species as their 

 parents, but further than this they tend to resemble 

 their parents in individual peculiarities. Thus, among 

 domestic cattle, the offspring resemble the parents in such 

 qualities as size, form, color, amount and quality of milk, 

 as well as many other qualities. 1 



iMetcalf, M. M. Organic Evolution, 3rd ed., 1911, p. 6. 

 3 



