io 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. 



Variation 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 



