g is more
odoriferous than other dogs. Isidore Geoffroy[47] gave to a dog the same
odour as that from a jackal by feeding it on raw flesh.

The belief that our dogs are descended from wolves, jackals, South American
Canidae, and other species, suggests a far more important difficulty. These
animals in their undomesticated state, judging from a widely-spread
analogy, would have been in some degree sterile if intercrossed; and such
sterility will be admitted as almost certain by all those who believe that
the lessened fertility of crossed forms is an infallible criterion of
specific distinctness. Anyhow these animals keep distinct in the countries
which they inhabit in common. On the other hand, all domestic dogs, which
are here supposed to be descended {31} from several distinct species, are,
as far as is known, mutually fertile together. But, as Broca has well
remarked,[48] the fertility of successive generations of mongrel dogs has
never been scrutinised with that care which is thought indispensable when
species are crossed. The few facts leading to the conclusion that the
sexual feelings and reproductive powers differ in the several races of the
dog when crossed are (passing over mere size as rendering propagation
difficult) as follows: the Mexican Alco[49] apparently dislikes dogs of
other kinds, but this perhaps is not strictly a sexual feeling; the
hairless endemic dog of Paraguay, according to Rengger, mixes less with the
European races than these do with each other; the Spitz-dog in Germany is
said to receive the fox more readily than do other breeds; and Dr. Hodgkin
states that a female Dingo in England attracted the male wild foxes. If
these latter statements can be trusted, they prove some degree of sexual
difference in the breeds of the dog. But the fact remains that our domestic
dogs, differing so widely as they do in external structure, are far more
fertile together than we have reason to believe their supposed wild parents
would have been. Pallas assumes[50] that a long course of domestication
eliminates that sterility which the parent-species would have exhibited if
only lately captured; no distinct facts are recorded in support of this
hypothesis; but the evidence seems to me so strong (independently of the
evidence derived from other domesticated animals) in favour of our domestic
dogs having descended from several wild stocks, that I am led to admit the
truth of this hypothesis.

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