Page 5 - My FlipBook

Pulex irritans, the so-called
human ea, is seen here under
magni cation. Such eas are
known to bite mammals, including
rats, mice, pigs, dogs, cats, bats,
monkeys, and humans, and
historically have spread deadly
diseases, notably bubonic plague.

More certain is that the effects of diseases on human popu-
lations worsened following the switch from hunting and gather-
ing to settled agriculture, which occurred sometime between ten
thousand and twelve thousand years ago. That watershed event
in humanity’s story signifi cantly changed people’s social habits,
making contracting and spreading those illnesses easier. Accord-
ing to McNeill:

Settling down to prolonged or permanent occupancy of a
single village site involved new risks of parasitic invasion.
Increased contact with human feces as they accumulated
in proximity to living quarters, for instance, could allow
a wide variety of intestinal parasites to move safely from
host to host. By contrast, a hunting band, perpetually on
the move . . . would risk little from this kind of infectious
cycle. We should expect that human populations living in
sedentary communities were therefore far more quickly
infested with worms and similar parasites than their hunt-
ing predecessors. 7

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