e
small hostile Indian or Malay tribes, who live in tropical regions and
often occupy only a few square leagues. The higher civilizations of
former times could not develop beyond a comparatively limited circle,
as their means of transport did not allow them to venture too far. The
conquest of the whole earth by modern civilization by means of the
mariner's compass, firearms, steam and electricity is thus an
absolutely contemporaneous event, unique in the history of the world,
the origin of which hardly goes back more than four hundred years.
This event has completely upset the natural internal evolution of
human races, by the fact that all the lower races attacked by
civilized races armed with guns and alcohol, are destined to rapid and
complete destruction.

Geology has discovered in the caves of the quaternary period, human
remains which are much lower in the scale of evolution and much nearer
the anthropoid apes than the lowest races still living. Their brain,
as shown by the cranial cavity, was still smaller. Lastly, _Dubois_
has discovered in Java the cranium of _Pithecanthropus erectus_ which
is intermediate between that of the orang-utan and man. If more such
remains are discovered the chain of transition between the apes and
man will be almost complete.

=Hybridity. Consanguinity.=--Before concluding this chapter we must
study the question of _hybrids_. It is important to know to what point
fecundity and descent are influenced by the degree of relationship
between the two procreators. Conjugation probably arises from the
general necessity of organisms to reenforce their race by variety.
Consanguinity perpetuated is harmful to the species, in the same way
as parthenogenesis, or indefinite reproduction by fission or budding.
It produces enfeeblement and degeneration of the race, and leads to
extinction by causing sterility.

By _consanguinity_ is meant continued sexual union between near
relatives. It is easy to understand that the conjugation of two germs
derived from brothers and sisters or from a father and his daughter
approaches parthenogenesis from the point of view of the mixing of
hereditary energies. We shall see later on that nearly all peoples
have a certain repugnance to consanguineous marriages. Among animals,
natural selection eliminates too consanguineous products.

On the other hand, sexual union between different species, however
little removed, gives no products. Near species may produce hyb