selections of slight
increments in the length of the limbs of individuals necessary to
produce a long-limbed breed, we might expect that such increments would
take place in different individuals (as we do not certainly know at what
period they do take place), some earlier and some later in the embryonic
state, and some during early youth; and these increments would reappear
in their offspring only at corresponding periods. Hence, the entire
length of limb in the new long-limbed breed would only be acquired at
the latest period of life, when that one which was latest of the
thousand primary increments of length supervened. Consequently, the
foetus of the new breed during the earlier part of its existence would
remain much less changed in the proportions of its limbs; and the
earlier the period the less would the change be.

{476} This seems to me to be more strongly stated here than in the
_Origin_, Ed. i.

Whatever may be thought of the facts on which this reasoning is
grounded, it shows how the embryos and young of different species might
come to remain less changed than their mature parents; and practically
we find that the young of our domestic animals, though differing, differ
less than their full-grown parents. Thus if we look at the young
puppies{477} of the greyhound and bulldog--(the two most obviously
modified of the breeds of dog)--we find their puppies at the age of six
days with legs and noses (the latter measured from the eyes to the tip)
of the same length; though in the proportional thicknesses and general
appearance of these parts there is a great difference. So it is with
cattle, though the young calves of different breeds are easily
recognisable, yet they do not differ so much in their proportions as the
full-grown animals. We see this clearly in the fact that it shows the
highest skill to select the best forms early in life, either in horses,
cattle or poultry; no one would attempt it only a few hours after birth;
and it requires great discrimination to judge with accuracy even during
their full youth, and the best judges are sometimes deceived. This shows
that the ultimate proportions of the body are not acquired till near
mature age. If I had collected sufficient facts to firmly establish the
proposition that in artificially selected breeds the embryonic and young
animals are not changed in a corresponding degree with their mature
parents, I might have omitted all the foregoing reasoning