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Sleeping on the ground

Subject: Sleeping on the ground
From: "Paul Crowley"
Date: Tue, 12 Jul 2005 13:13:49 +0100
Newsgroups: sci.anthropology.paleo
There are 12 hours of dark in every 24, and the
manner in which an animal uses, or disposes
of, its limbs in those hours (the greater part of
its existence) is a matter of crucial importance
in its evolution.  Chimps have four 'hands' at
the end of each limb, and use all of them to hold
on to branches.  This is especially the case in
windy weather, or when they have to go high
in the trees to minimise the risk of predation.

At some point in our evolution, our ancestors
stopped sleeping in trees.  This represented a
major change in niche.  No longer were they
bound to find, each night, a 'sleeping tree' -- 
one that would provide a fairly comfortable
night and was relatively safe from nocturnal
predators. They could move into territory
quite devoid of such trees.

Sleeping on the ground brought in sets of new
and entirely different problems.  Firstly, the
hominid territory had to be effectively free of
nocturnal predators.  Hominids on the ground
at night, especially hominid young, are
extremely vulnerable.  The initial hominid
population must have evolved in a predator-
free location (probably an island).  Later, once
they began to exploit typical mainland locations,
one of the principal functions of hominid adult
males would have been to keep their territory
clear of predators by constant patrolling, and
then killing or harassing any they located.

Sleeping on the ground would have made the
sexual dominance by an alpha-male of a harem
impossible.  The basis for chimp-style mating
systems would have ceased to exist. However,
females and their young would have been
vulnerable in the dark to attack by stranger
males, as well as in danger from other hazards,
such as smaller predators like jackals (on
babies).  Monogamy would have come in at
this point, partly to help minimise these
problems.

For some strange reasons (probably mostly
historical) standard PA fails to recognise the
enormity of the changes brought in by the
switch to sleeping on the ground.
(Presumably the 'thinking' involved here
originated in the absence of any concept of
niche.)  There can be no doubt that the switch
was integral with the evolution of bipedalism.

Defecation (of faeces or urine) by an infant at
night is no problem when the mother-infant
dyad is sleeping in a tree.  The execreta will
harmlessly fall out of the tree.  But it will be a
serious matter when both are sleeping on the
ground.  The mother will find it much more
convenient to make up a separate sleeping
ground-nest for her infant, close to her own.
The moss, dried grass, etc., used to form it
will have to be renewed frequently, but her
own bedding will remain uncontaminated.

For the previous 30-40 million years or so,
the physical link between the mother and her
infant operated on a 24/7 basis.  At this point
it is broken, and the infant sleeps in its own
'cot'.  The mother can leave it there during
daylight hours as well.  For the first time, she
is able to stand upright, without the weight
of an infant on her belly.  Infant altriciality
evolves rapidly at this time;  over-active
infants that crawl out of their nests during
the night or the day, will be rapidly selected
out.

The immediate cause for this shift was
probably the same as that for bipedalism in
males: the need to be able to carry a club.
Females may have wielded them in action
relatively rarely, but from a distance, or when
partially obscured by trees, a female with a
club would often have been indistinguishable
from a male, and the more numerous a club-
wielding group appeared, the less likely it
was to be attacked.

The primary responsibility of females was
always infant- and child-rearing.  In later
hominid societies with larger groups, females
would have adopted the modern human
pattern of staying at home while males went
to war.  But the first female bipeds, living in
quite small groups, were probably more
immediately involved in the defence of their
territory.  The species would have exhibited
relatively little sexual dimorphism at this
point.

Both infant nakedness and infant fat would
also have evolved at this time.  It was
difficult to keep infant nests dry, especially
in the rainy season. Damp ground,  rain,
condensation, and infant pee, all made it
very difficult for the infant to stay warm and
dry at night.  The infant, sleeping on its own,
would not have benefited from the warmth
of its mother.  Hair is worse than useless in
damp conditions, and infant nakedness
rapidly evolved, as did subcutaneous infant
fat, to provide better insulation.  Adults also
evolved substantial nakedness, with some
subcutaneous fat, for essentially the same
reasons.

This evolution would have taken place at
great speed in a small, isolated population.
This population found a new niche, and
rapidly evolved into it, swiftly taking on
almost all the adaptations that make the
taxon distinctive.  They are all inter-linked
and, as with all other species, they form a
solution to a complex problem set by the
niche.


Paul.



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