THE BIOLOGY OF TWINS 165 
mammals which were kept from earliest youth in 
peculiar conditions of artificial nurture and took on 
the ways and habits of their unrelated comrades; 
that many cases are known among children where 
those transplanted early from deteriorative to 
wholesome conditions have developed well; and that 
the changes of nurture in Galton’s cases were within 
very narrow limits. Hereditary “nature” is 
indeed the seed-corn; nurture is the sunshine and 
the soil, the wind and the rain. When both com- 
ponents of a resultant are essential, it does not seem 
to matter very much which we call the more im- 
portant. The fundamental factors of all sorts of 
characters are in the germ, but the precise expres- 
sion they find in development depends in some 
measure on the nurture. 
