f the two things
depends on the instinctive necessity of health, combined with the
sexual appetite, although custom has produced numerous aberrations.
Everything which differs markedly from the type of the race is more
or less pathological. This is why instinct, determined by natural
selection, repels it.

Fashion also rules among savages, but is less changeable among them
than with us, and their taste for adornment only varies in the narrow
circle of their customs.

Climate has a powerful action on the types of races, the latter being
generally adapted to the climate in which they live. Thus, the
European becomes darker in the tropics while negroes and Indians
become paler in the north.

LAWS OF RESEMBLANCE--HYBRIDS

Every animal species has an instinctive repugnance to pair with
another. Even where they are possible, natural hybrids are rare, and
only become a little more frequent in domestic animals and plants. The
fecundity of hybrids diminishes when they have connection among
themselves, and this explains why the instinct for such connections
tends to gradually disappear.

In his book on "The Mneme," Semon explains the infecundity of hybrids
in a very plausible manner, by the disorder that a too large quantity
of dissimilar hereditary engrams causes in the hereditary mneme of two
conjugated cells. When the parents differ from each other only in a
moderate degree homophony may still be reestablished, and then the
divergencies have a very favorable effect on the product, by the new
combinations which they furnish in the course of its development.

Moral ideas follow the course of instincts, and this explains why
sexual connection with animals is regarded as a horrible crime. This
is especially produced by pathological aberration, or when one sex is
completely isolated from the other. There is also a certain degree of
aversion to copulation between different races, in animals as well as
man; for example, between sheep and horses of different races, and
between white men, negroes and Indians. There are, however, many
hybrids or half-breeds in South America, and in Mexico they even
constitute two-thirds of the population.

Broca maintained that human hybrids produced by the crossing of remote
races, for example, between English and negroes or Australians, were
usually sterile. Westermark disputes this, but agrees that these
hybrids become enfeebled in a few generations. It has also been
established that mixe