lo HEREDITY AND INHERITANCE 



be transmitted from generation to generation. In short, the 

 fundamental importance of inheritance was long ago demon- 

 strated up to the hilt. 



It remains, however, (i) to make the evidence of transmissibility 

 more precise and systematic ; (2) to inquire into the trans- 

 missibility of subtle characters such as longevity and fecundity ; 

 (3) to discover the different degrees of transmissibility, for some 

 characters are much more heritable than others ; and (4) to 

 classify different modes of hereditary resemblance — e.g. blending 

 of the characters of the two parents, taking after the father in 

 one feature and after the mother in another, apparently resem- 

 bling one parent only, rehabilitating a grandsire's features, 

 harking back to a remoter ancestor, and so on. What happens 

 when there is close in-breeding or pairing within a narrow radius 

 of relationship ? What happens when two hybrids are paired ? 

 In what sense, if any, is a disease heritable ? These and many 

 similar questions will be discussed in our inquiry into the facts 

 of inheritance. 



Yariation — Whenever we begin to compare the characters 

 of an organism with those of its parents, we discover that the 

 familiar saying, " Like begets like," must be modified into, " Like 

 tends to beget like." On the one hand, the child is like its 

 parents, " a chip of the old block," a literal reproduction ; on 

 the other hand, the child is something original, a new pattern, 

 a fresh start — leading the race. We do not gather grapes of 

 thorns, or figs of thistles ; yet two brothers may be very unlike 

 one another or either of their parents, and even the peas in one 

 pod may be different. On the one hand, there is a tendency 

 towards continuity, towards persistence of characters, towards 

 complete hereditary resemblance — in short, a kind of organic 

 inertia in a family or stock or species. On the other hand, there 

 is a tendency towards variation, towards new departures, to- 

 wards incomplete hereditary resemblance, or much more than 

 that. It is necessary to hold the balance between these two 



