n hemisphere, we find the Malays and
Malayo-Polynesians, differentiated offshoots of the Mongolian stock,
restricted to the Tropics, except where Polynesians have spread to
outlying New Zealand. The Chinese draw their political boundary nearly
along the Tropic of Cancer, but they have freely lapped over this
frontier into Indo-China as far as Singapore.[197] Combined with this
expansion was the early infiltration of the Chinese into the
Philippines, Borneo, and the western Sunda Isles, all distinctly
tropical. The fact that the Chinese show a physical capacity for
acclimatization found in no other race explains in part their presence
into the Tropics. In contrast, the Aryan folk of India, whether in their
pure type as found in the Punjab and Rajputana Desert, or mingled with
the earlier Dravidian races belong to the hot belt but scarcely reach
the Tropic of Cancer,[198] though their language has far overshot this
line both in the Deccan and the Ganges Delta. One spore of Aryan stock,
in about 450 B.C., moved by sea from the Bay of Cambay to Ceylon;
mingling there with the Tamil natives, they became the progenitors of
the Singhalese, forming a hybrid tropical offshoot.

Europe, except for its small sub-arctic area, has received immigrants,
according to the testimony of history and ethnology, only from the
temperate parts of Asia and Africa, with the one exception of the
Saracens of Arabia, whose original home lay wholly within the hot
climate belt of 20 deg.C. (68 deg.F.). Saracen expansion, in covering Persia,
Syria, and Egypt, still kept to this hot belt; only in the Barbary Coast
of Africa and in Spain did it protrude into the temperate belt. Though
this last territory was extra-tropical, it was essentially semi-arid and
sub-tropical in temperature, like the dry trade-wind belt whence the
Saracens had sprung.

[Illustration: ETHNOGRAPHICAL MAP OF AFRICA AND ARABIA.]

[Sidenote: Range of movements in Africa.]

The Semitic folk of Arabia and the desert Hamites of northern Africa,
bred by their hot, dry environment to a nomadic life, have been drawn
southward over the Sahara across the Tropic into the grasslands of the
Sudan, permeating a wide zone of negro folk with the political control,
religion, civilization and blood of the Mediterranean north. Here
similar though better conditions of life, a climate hotter though less
arid, attracted Hamitic invasion, while the relatively dense native
population in a lower stag