es of greyhounds so manifestly
adapted to speed of foot, or the delicate powers of smell in
pointers and setters, or a dozen cases of modified structure
effected by artificial selection."

In none of the assertions contained in this passage can I agree. Had the
inheritance of "functional and structural decline" been "not generally
disputed," half my argument would have been needless; and had the
inheritance of "increased strength and development" caused by use been
recognized, as "illustrated by many examples," the other half of my
argument would have been needless. But both are disputed; and, if not
positively denied, are held to be unproved. Greyhounds and pointers do
not yield valid evidence, because their peculiarities are more due to
artificial selection than to any other cause. It may, indeed, be doubted
whether greyhounds use their legs more than other dogs. Dogs of all
kinds are daily in the habit of running about and chasing one another at
the top of their speed--other dogs more frequently than greyhounds,
which are not much given to play. The occasions on which greyhounds
exercise their legs in chasing hares, occupy but inconsiderable spaces
in their lives, and can play but small parts in developing their legs.
And then, how about their long heads and sharp noses? Are these
developed by running? The structure of the greyhound is explicable as a
result mainly of selection of variations occasionally arising from
unknown causes; but it is inexplicable otherwise. Still more obviously
invalid is the evidence said to be furnished by pointers and setters.
How can these be said to exercise their organs of smell more than other
dogs? Do not all dogs occupy themselves in sniffing about here and there
all day long: tracing animals of their own kind and of other kinds?
Instead of admitting that the olfactory sense is more exercised in
pointers and setters than in other dogs, it might, contrariwise, be
contended that it is exercised less; seeing that during the greater
parts of their lives they are shut up in kennels where the varieties of
odours, on which to practise their noses, is but small. Clearly if
breeders of sporting dogs have from early days habitually bred from
those puppies of each litter which had the keenest noses (and it is
undeniable that the puppies of each litter are made different from one
another, as are the children in each human family, by unknown
combinations of causes), then the exist