With respect to the precise causes and steps by which the several races of
dogs have come to differ so greatly from each other, we are, as in most
other cases, profoundly ignorant. We may attribute part of the difference
in external form and constitution to inheritance from distinct wild stocks,
that is to changes effected under nature before domestication. We must
attribute something to the crossing of the several domestic and natural
races. I shall, however, soon recur to the crossing of races. We have
already seen how often savages cross their dogs with wild native species;
and Pennant gives a curious account (1/74. 'History of Quadrupeds' 1793
volume 1 page 238.) of the manner in which Fochabers, in Scotland, was
stocked "with a multitude of curs of a most wolfish aspect" from a single
hybrid-wolf brought into that district.

It would appear that climate to a certain extent directly modifies the
forms of dogs. We have lately seen that several of our English breeds
cannot live in India, and it is positively asserted that when bred there
for a few generations they degenerate not only in their mental faculties,
but in form. Captain Williamson (1/75. 'Oriental Field Sports' quoted by
Youatt 'The Dog' page 15.), who carefully attended to this subject, states
that "hounds are the most rapid in their decline;" "greyhounds and
pointers, also, rapidly decline." But spaniels, after eight or nine
generations, and without a cross from Europe, are as good as their
ancestors. Dr. Falconer informs me that bulldogs, which have been known,
when first brought into the country, to pin down even an elephant by its
trunk, not only fall off after two or three generations in pluck and
ferocity, but lose the under-hung character of their lower jaws; their
muzzles become finer and their bodies lighter. English dogs imported into
India are so valuable that probably due care has been taken to prevent
their crossing with native dogs; so that the deterioration cannot be thus
accounted for. The Rev. R. Everest informs me that he obtained a pair of