Re: Anyone want to discuss paleoanthropology?

The savanna nonsense is still not dead:

The Evolution of Body Heat Conductivity, Skin
and Brain Size in Human
AI Ibraimov 2007 JHE 21:95-103
What is unusual about the human brain is that
we are the only largish mammal whose brain size
kept pace with our growth in body size.

(if we want to understand why we have a large
brain, we have to compare to other large-brained
mammals: arboreals (eg, many primates) have typically
brains twice as large as terrestrials, (semi)
aquatics have typically brains 3 times as large as
comparable land mammals, we descend from arboreals &
have always been waterside animals, no wonder our
brains are about 6 times as big as could be expected
in equally large terrestrials - has nothing to
do directly with our skin)

The plausible reason of this phenomenon is his skin, when
after having lost its hair it became the largest and almost
universal organ of sense, which begins functioning as early
as in the prenatal period of human development.

(pure fantasy: the man is raving)

???
Why is it fantasy?

He thinks "this phenomenon" (very large brain) is explained by our skin...
It's true that several furless spp have large brains (Cetacea, elephants),
but rhinos & seacows are furless & rel.small-brained. Why on earth must
naked mammals have large brains or v.v.?? (The savanna loons will probably
say: we need a very strong cooling mechanism to protect our large brain from
overheating in the hot savanna... :-D)

Besides, he is in the illusion that a fur is no "universal organ of
sense"...

Seldom seen such nonsense.

It is assumed that H.sapiens became the possessor
of the largest brain among the primates after he
has lost hair on his skin. Apparently skin became
hairless as a result of evolution of condensed
chromatin in the genome of the direct ancestors
of a modern human. In particular in their karyotypes
together with chromosomal Q-heterochromatin regions
3 pairs of autosomes (1, 9 & 16), and Y chromosome
became the carriers of unusually large
C-heterochromatin regions, which have lead to
significant increase of body heat conductivity.

(as in other naked mammals such as whales,
seacows, hippos etc...)

In conditions of tropical Africa, where our
ancestors inhabited,

(ah? the author postulates savanna)

That was my impression, on reading his paper.
Also disagreed, with his conclusion that being
relatively hairless preceded the increase in
brain size (if that were the case most of the
other large apes, would be hairless too).

Fossils can't help us here. We have only embryological data.
My impression:
- Apes have about the same EQ as NWMs (OWMs could have slightly reduced CC
after becoming more ground-dwelling?).
- Afr.ape fetuses are furless prenatally.
- Brain enlargement is obvious since Mojokerto c 1.8 Ma with estimated CC as
an adult 800-99 cc.
So I think that the author is right when he believes that our furlessness
preceded our great brain enlargement.


availability of skin covered with hair became a
serious obstacle in keeping the temperature
homeostasis, particularly in dissipation
of excessive heat from the organism that finally
has lead to hairlessness.

(ridiculous nonsense: if we want to know why we
are naked we have to compare to other naked mammals:
medium-sized tropical waterside mammals like
babirusas are typically naked)

There are no other large brained naked primates
to make comparisons with.

We don't need these.
1) We have consider CC & furlessness apart. It's a common mistake (esp.by
savanna believers: hot>sweat>naked>fat) trying to link things that have
nothing to do with each other.
2) We can compare both to non-primate spp. Bat wings can be compared to bird
wings. The combination of fat & furless (independent from each other) is
only seen in (semi)aquatic mammals (all of which are non-primate). Only
savanna-biased people think humans must be an exception.

IMO he is correct in saying body hair is an
obstacle to sweating. For example, for sweating
to be 100 % effective the skin has to be
relatively hairless, an bare.

I'm not sure (AFAIK patas monkeys sweat in furred regions), but it's well
possible.

A comparison would be wearing a tight shirt while
sweating, the shirt would get damp, but the body
would lose very little of the heat it is
trying to shed ...

Yes, not unlikely.

About 90 % of body heat is lost through the
skin. We lose heat by conduction, convection
and sweating, and of the three sweating is the
most of effective, short of jumping into a pool
of cold water (not recommended - as rapid
cooling in water, can be fatal).

One strategy by savanna mammals it letting your temperature go up, but
humans (as expected for waterside endotherms) are unable to do that. "Real"
savanna mammals have brains that can tolerate up to 45°C. Aquatic mammals
OTOH have brains with rel.low temperatures (36-37°C).

Given this, the heat protection function of the
hair cover was taken over by a large amount of
subcutaneous adipose tissue.

(even bigger nonsense:
- fur, SC fat : mammoth, seal...
- fur, no fat : most mammals incl.chimps, baboons...
- SC fat, no fur : Cetacea, human...
- no fat, no fur : naked molerat, elephant...
IOW, fat & fur evolved independently, as adaptations
to different things)

Not so sure it is nonsense ...
Both could have easily evolved independently
in early Homo, but once we became relatively
hairless ... SC fat could have taken on the
additional role. ---m3d

IMO fat & fur have to be considered apart: some mammals are fat, some are
furred, some are both, some are neither. Only in small semi-aquatics a very
dense fur (sea otter) can compensate for the absence of a thermo-insulative
fat layer, but this is not so in medium-sized (humans) & large mammals. All
non-tropical semi-aquatic mammals (unless very big, like male sea-elephants)
need a fur for thermo-insulation on land. It's not because we're fat that
could lose of fur.

http://www.krepublishers.com/02-Journals/JHE/JHE-21-0-000-000-2007-Web/JHE-2
1-2-000-000-2007-Abstract-PDF/JHE-21-2-095-103-2007-1528-Ibraimov-A-I/JHE-21
-2-095-103-2007-1528-Ibraimov-A-I-Tt.pdf
or google "hominid sweating Ibraimov"

--Marc

.

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