of
plants, the larger animals play their part. Insects are, in numberless
instances, borne along in the coats of animals, or the feathers of
birds; and the eggs of some species are capable, like seeds, of
resisting the digestive powers of the stomach, and after they are
swallowed with herbage, may be ejected again unharmed in the dung.

_Geographical Distribution and Diffusion of Man._

I have reserved for the last some observations on the range and
diffusion of the human species over the earth, and the influence of man
in spreading other animals and plants, especially the terrestrial.

Many naturalists have amused themselves in speculating on the probable
birth-place of mankind, the point from which, if we assume the whole
human race to have descended from a single pair, the tide of emigration
must originally have proceeded. It has been always a favorite
conjecture, that this birth-place was situated within or near the
tropics, where perpetual summer reigns, and where fruits, herbs, and
roots are plentifully supplied throughout the year. The climate of these
regions, it has been said, is suited to a being born without any
covering, and who had not yet acquired the arts of building habitations
or providing clothes.

_Progress of Human Population._--"The hunter state," it has been argued,
"which Montesquieu placed the first, was probably only the second stage
to which mankind arrived; since so many arts must have been invented to
catch a salmon, or a deer, that society could no longer have been in its
infancy when they came into use."[935] When regions where the
spontaneous fruits of the earth abound became overpeopled, men would
naturally diffuse themselves over the neighboring parts of the temperate
zone; but a considerable time would probably elapse before this event
took place; and it is possible, as a writer before cited observes, that
in the interval before the multiplication of their numbers and their
increasing wants had compelled them to emigrate, some arts to take
animals were invented, but far inferior to what we see practised at this
day among savages. As their habitations gradually advanced into the
temperate zone, the new difficulties they had to encounter would call
forth by degrees the spirit of invention, and the probability of such
inventions always rises with the number of people involved in the same
necessity.[936]

A distinguished modern writer, who coincides for the most part in the
views ab