Re: Parasites and paleoanthropology
Paul Crowley (Paul@crowleyp.demon.co.uk)
Sat, 20 Jul 96 14:23:46 GMT
In article <4sqboc$lgc@lyra.csx.cam.ac.uk>
nmm1@cus.cam.ac.uk "Nick Maclaren" writes:
> So animals without fixed home bases don't have species-specific
> exoparasites (of the flea type)? Well, well, well. I learn something
> new every day :-)
Fleas jump on for a feed and then jump off. If the host never
returns to base they die. So chimps and gorillas don't have them.
> > ... Let's say
> > it was proved that the Guinea worm (dracunculus) speciated at
> > 1 mya; we'd have good evidence that before that time hominid
> > populations were in permanent residence around the types of
> > water holes inhabited by certain species of water snails and
> > that they had achieved a certain level of population density.
> > This information could point to a definite type of habitat and
> > indicate probable diets.
>
> Er, no. What it would demonstrate is that the probabilities of
> humans returning to specific water holes (and not necessarily the
> same humans) are high enough for a stable state. This does not show
> permanent residence.
It *might* be possible for dracunculus to survive in a nomadic
population that shared the same water holes. I doubt it. I'd
want to see evidence, which should be obtainable from say the
!Kung or the Berbers. I understand that the period of
infectivity for an adult worm is short (about 2 weeks) and
largely incapacitates the host. A painful sore appears on the
leg, through which the worm pours its eggs when the sore is
submerged in water. This has to occur in a pool with the right
species of snails. The parasite lives in the snails for a while
and then moves to a crustacean which is consumed by humans when
they drink the water. Again the crustacean must both acquire
the parasite and be consumed at the right time. A parasitic life
is full of problems; this one can't survive in a stream, nor
drying out. Dracunculus is being eliminated by the WHO by means
of a program of (a) treating infected hosts and stopping them
from walking in open wells (b) killing the snails where water is
drawn, and (c) getting everyone to strain their drinking water
through a cloth to avoid ingesting the crustaceans. Dracunculus
is close to extinction.
> In fact, the existence of water-borne parasites does not even show
> that humans used permanent water-holes. If the parasite can last a
> complete dry season in either the human or the dormant phase of the
> aquatic host, then it can be transmitted entirely via transient water
> holes and streams.
You should not be so dogmatic when you are so ignorant. The human
flea (which is not water-borne) indicates fixed home bases, which
implies permanent water-holes. Each of the 200 or so macroparasites
needs to be studied *and_the_results_correlated* together. I'd be
surprised if many of them did not clearly indicate permanent and
fairly dense hominid populations. The main uncertainty, as I see
it, is "how long ago?". DNA and other studies could tell us that.
Paul.
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