Chapter II 



HEREDITY, VARIATION AND DEATH 



HEREDITY is so familiar a thing that we have ceased to wonder The 

 at it. It is a matter of course that children should be like their a " cient 



theory 



parents, that an acorn should grow into an oak, an orange pip 

 into an orange tree. But whenever men have reflected seriously 

 on the matter, it has filled them with astonishment. The old 

 theory was that the acorn contained a tiny oak tree which " un- 

 folded " and so became a giant of the forest ; and not only that, 

 but within the tiny embryo tree was another tiny embryo and 

 within that another. If it was not so, where did the oak come 

 from ? The reasoning was perfectly sound, but when good 

 microscopes were obtainable, men looked for the oak tree and it 

 was not to be found. 



No actual oak tree is there, yet a potential oak there is. Plant 

 an acorn and it will be proved. In the same way the chicken 

 must be potentially in the egg before incubation has taken place 

 though no chicken is to be seen. And here another question 

 arises : an egg is the mother of the hen, but is a hen the mother 

 of the eggs she lays? Professor Weismann says "certainly 

 not" and the world is coming to agree with him. The egg and 

 the hen that lays it are both sprung from the same egg. In the 

 line of descent egg follows egg ; each, if it hatches, becomes the 

 mother of a chick and, if the chick be a hen bird, of other eggs 

 also that may in time be laid and duly sat upon and hatched. This 

 is the theory that Professor Weismann has spent years in maintain- 

 ing, and since the inferences that may be drawn from it are of the 

 utmost importance, I shall try to state his views as clearly as I can. Br . f 



" The nucleus of the reproductive cell bears all the hereditary ment of 

 characters : and it is almost certain that it is not the whole Weis ; 



mann s 



nucleus but the loops of chromatin that have this function : views 



19 



