They are nature's
miserable castaways, parasitical tribes lost in a great dry wilderness
where no blood is; and every marsh-born mosquito, piping of the hunger
gnawing its vitals, and every forest tick, blindly feeling with its
grappling-irons for the beast that never brushes by, seems to tell us of
a world peopled with gigantic forms, mammalian and reptilian, which once
afforded abundant pasture to the parasite, and which the parasite
perhaps assisted to overthrow.
It is almost necessary to transport oneself to the vast tick-infested
wilderness of the New World to appreciate the full significance of a
passage in Belt's _Naturalist in Nicaragua,_ in which it is suggested
that man's hairless condition was perhaps brought about by natural
selection in tropical regions, where he was greatly troubled with
parasites of this kind. It is certain that if in such a country as
Brazil he possessed a hairy coat, affording cover to the tick and
enabling it to get a footing on the body, his condition would be a very
sad one. Savages abhor hairs on the body, and even pluck them off their
faces. This seems like a survival of an ancient habit acquired when the
whole body was clothed with hair; and if primitive man ever possessed
such a habit, nature only followed his lead in giving him a hairless
offspring.
Is it not also probable that the small amount of mammalian life in South
America, and the aquatic habits of nearly all the large animals in the
warmer districts, is due to the persecutions of the tick?
The only way in which a large animal can rid itself of the pest is by
going into the water or wallowing in the mud; and this perhaps accounts
for the more or less aquatic habits of the jaguar, aguara-guazu, the
large Cervus paluclosus, tapir, capybara, and peccary.
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