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I do not say that the giraffe or its ancestors have not had 
the best of it when there was a struggle for existence, and 
that natural selection has not played its part; the fact of the 
giraffe’s existence is proof enough that it was better adapted to 
its environment than some of its competitors; and the longer 
the neck grew doubtless the greater superiority the animal 
would possess. 
As to the short-necked forms which would connect the 
present giraffe with the stock from which it originally came, 
their dying out is not difficult to explain. The law of earlier 
inheritance allows us to imagine a small beginning becoming 
more accentuated in all members of a species as time goes on; 
and as the shorter-necked forms were really the parents of the 
longer-necked forms the disappearance of the former would be 
due, as the lawyers say of a lease, to effluxion of time. 
Arising from and co-existing with developmental variation 
there seems to be another factor important in differentiating 
species ; and this is the time when the offspring is produced. 
Offspring produced early and offspring produced late in the 
life of a parent shewing considerable developmental changes 
between early and late maturity, or between early maturity and 
senility, would in all probability differ to a certain extent. It 
is, I think, reasonable to suppose that if there were, say, a 
decline of vigour after a certain period of the parent’s life, the 
offspring produced after this time would be more likely not 
only to be somewhat less vigorous altogether, but would 
probably exhibit declining vigour at an earlier age than those 
produced before any decline of vigour set in. 
This seems to be a reasonable deduction from what is 
observed in phylogenetic series of Ammonites, where from the 
same stock arise one series which continue to progress, another 
series which retrograde, though both lived together and were 
presumably subject to the same environment. 
More marked still would be the effects if from any cause 
there arose a difference among members of a species as to the 
time in their lives when offspring were produced. There is the 
case in Man—the professional classes defer marriage till late 
in life, agricultural labourers marry very early. 
