and plant
geography requires a previous knowledge of the various means of
dispersal, active and passive, possessed by these lower forms of life,
so anthropo-geography must start with a study of the movements of
mankind.

[Sidenote: Mobility of primitive peoples.]

First of all is to be noted an evolution in the mobility of peoples. In
the lower stages of culture mobility is great. It is favored by the
persistent food-quest over wide areas incident to retarded economic
methods, and by the loose attachment of society to the soil. The small
social groups peculiar to these stages and their innate tendency to
fission help the movements to ramify. The consequent scattered
distribution of the population offers wide interstices between
encampments or villages, and into these vacant spaces other wandering
tribes easily penetrate. The rapid decline of the Indian race in America
before the advancing whites was due chiefly to the division of the
savages into small groups, scattered sparsely over a wide territory.
Hunter and pastoral peoples need far more land than they can occupy at
any one time. Hence the temporarily vacant spots invite incursion.
Moreover, the slight impedimenta carried by primitive folk minimize the
natural physical obstacles which they meet when on the march. The
lightly equipped war parties of the Shawnee Indians used gorges and gaps
for the passage of the Allegheny Mountains which were prohibitive to all
white pioneers except the lonely trapper. Finally, this mobility gets
into the primitive mind. The _Wanderlust_ is strong. Long residence in
one territory is irksome, attachment is weak. Therefore a small cause
suffices to start the whole or part of the social body moving. A
temporary failure of the food supply, cruelty or excessive exaction of
tribute on the part of the chief, occasions an exodus. The history of
every negro tribe in Africa gives instances of such secessions, which
often leave whole districts empty and exposed to the next wandering
occupant. Methods of preventing such withdrawals, and therewith the
diminution of his treasury receipts and his fighting force, belong to
the policy of every negro chieftain.

[Sidenote: Natural barriers to movement.]

The checks to this native mobility of primitive peoples are two:
physical and mental. In addition to the usual barriers of mountains,
deserts, and seas before the invention of boats, primeval forests have
always offered serious obstacles to man