Re: Waking up covered in dew
Paul Crowley (Paul@crowleyp.demon.co.uk)
Thu, 05 Sep 96 18:36:06 GMT
In article <50k17n$nnk@lyra.csx.cam.ac.uk>
nmm1@cus.cam.ac.uk "Nick Maclaren" writes:
> |> Would you sleep up in a tree in order to avoid cold?
>
> Yes, and I do! In radiative conditions (e.g. savannah and not
> jungle), the coldest air is near the ground (i.e. exactly the
> converse of during the day). A hammock is often warmer than a
> tent, as I can witness - though much of that is due to reduced
> conduction through the ground.
I take your points about open country. I was thinking about apes
in a forest. However, I don't want the basic question forgotten:
At some point (proto-?) hominids left the trees and started sleeping
on the ground. When and where was this? No one suggests that they
had fire, shelter or blankets at that time. So either they did it
in a location with a warm night ground temperature OR they had
hair and lost it later for some compelling (if unknown) reason.
> If there is one cold spell every
> 10 years severe enough to kill even 10% of immature animals, this is
> a massive evolutionary pressure. Any mutation that halves this
> death rate could have significant disadvantages and still spread
> throughout the population over hundreds of millenia.
Your point is sound (even if your figures seem a bit extreme to
me). The easiest mutation would be to re-grow the hair; it's
not an uncommon one in modern Hss.
Surely all this has got to mean that until recently (say about
75 kya) our ancestors lived in locations with warm nightime
temperatures. The fact that some populations survived outside
their *natural* habitat by means of fire, shelter and blankets
does not invalidate this conclusion.
Paul.
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