Marc Verha
Thu, Nov-29-07, 06:16
MJ Rantala 2007 J.Zool.273:1-7 Evolution of nakedness in
Homo sapiens
Homo sapiens L. is the only existing primate species lacking
in functionally effective thermally insulating fur. As all
other primates have considerable hair covering, it has always
been accepted that our ancestors must once have had a
respectable amount of body hair. Unfortunately, fossils cannot
help us when it comes to differences in skin and hair. Recent
DNA analysis, however, has given us some idea of when and
where the great denudation took place. A number of hypotheses
have been proposed to account for this feature, but none of
these has gained general acceptance. In this paper, I present
these hypotheses in the light of current empirical evidence
and discussion.
...
The aquatic ape hypothesis, put forth by Hardy (1960), assumes
that hominids were forced by interspecies competition from an
arboreal life to feeding on the seashore, hunting for food
for example, shellfish and sea-urchins, and thus gradually
becoming more adapted to swimming. In time, hominids became
increasingly aquatic, moving further and further out from the
shore. Humans therefore lost their long, shaggy coat of fur,
which is typical of primates but not of marine animals. This
streamlining improved our smooth passage through the water
(Hardy, 1960). The aquatic ape theory was subsequently
elaborated by Morgan (1972, 1982, 1985, 1990), Morris (1977,
1994), Cuanne
(1980), La Lumiere (1981), Ellis (1986), Verhaegen (1985,
1987) and Evans
(1981). The nakedness of some aquatic mammals, such as whales,
manatees and dolphins, has been cited as evidence to
support the hypothesis that man may have an aquatic
ancestor (e.g. Hardy, 1960). Nakedness is naturally
advantageous to these aquatic mammals because it
reduces drag and buoyancy (Wheeler, 1985). Once
insulating fur is removed, however, excessive heat
loss is an even greater problem than for terrestrial
species, as water has a higher thermal conductivity
than air (Wheeler, 1985). Most of the diverse
mammalian groups that have adopted an aquatic mode of
life have therefore retained a dense covering of body
hair (Sokolov, 1962; Wheeler, 1985). Most of the
aquatic mammals that have lost their hair have large
and fusiform bodies with small appendages; large
animals possess low thermal conductances, while small
appendages minimize the area of skin in contact with
water (Wheeler, 1985). Furthermore, heat loss from the
extremities is restricted among these mammals by
vascular adaptation, such as heat-exchanging rates at
the base of the flippers (Scholander & Schevill,
1982). Neither of these properties, however, applies to early
hominids; it is therefore difficult to reconcile the
hairless condition of humans with an aquatic existence
(Wheeler, 1985). A naked mammal of the shape and size of
the early hominids or modern humans would have found
maintaining a high body temperature in the sea
energetically very expensive. Even those species of
comparable body mass that inhabit warm tropical
freshwater bodies have retained a thick coat (Wheeler,
1985). There is, furthermore, no fossil evidence to
support the aquatic ape hypothesis, although human fossil
remains are often found near bodies of water (Foley,
1987). It is not very realistic to claim that humans have
ever lived such a totally aquatic life as those marine
mammals that have shed their fur. It is more likely that
our ancestors lived on the shore and caught their food
offshore by wading and diving. Humans would naturally
have returned to the beach to sleep, and would have spent
most of their time ashore. At night, insulating fur would
have been an advantage. ...
_____
Outdated version of AAT (most recent Morgan 1990).
Nobody ever suggested that our ancestors ever lived a
totally aq.life.
Wheeler's papers are irrelevant nonsense here: Accounts of how
our Plio-Pleistocene ancestors may have lived on the savannah
include bouts of strenuous activity outside the gallery forest
for hunting or digging; dogged pursuit of swifter animals over
one or two days; and bipedal trekking after migrating herds of
savannah ungulates. Some of the even more imaginative versions
appear mutually contradictory. For example, the hypothesis of
a foraging or hunting male accords ill with the meridian
theory of Wheeler that our ancestors became bipedal to
minimise direct solar radiation at midday and retained a hairy
heat shield only on top of the head (1984, 1988, in imitation
of DHK Lee in Newman 1970 & in Schmidt-Nielsen 1974:89). If we
accept this reasoning, it must have been the women who ranged
over the plains at noon while the balding and bearded males
rested in the shade.
I'll place the paper in the AAT files within a few days.
--Marc Verhaegen http://groups.yahoo.com/group/AAT
http://users.ugent.be/~mvaneech/outthere.htm
http://users.ugent.be/~mvaneech/Symposium.html
Homo sapiens
Homo sapiens L. is the only existing primate species lacking
in functionally effective thermally insulating fur. As all
other primates have considerable hair covering, it has always
been accepted that our ancestors must once have had a
respectable amount of body hair. Unfortunately, fossils cannot
help us when it comes to differences in skin and hair. Recent
DNA analysis, however, has given us some idea of when and
where the great denudation took place. A number of hypotheses
have been proposed to account for this feature, but none of
these has gained general acceptance. In this paper, I present
these hypotheses in the light of current empirical evidence
and discussion.
...
The aquatic ape hypothesis, put forth by Hardy (1960), assumes
that hominids were forced by interspecies competition from an
arboreal life to feeding on the seashore, hunting for food
for example, shellfish and sea-urchins, and thus gradually
becoming more adapted to swimming. In time, hominids became
increasingly aquatic, moving further and further out from the
shore. Humans therefore lost their long, shaggy coat of fur,
which is typical of primates but not of marine animals. This
streamlining improved our smooth passage through the water
(Hardy, 1960). The aquatic ape theory was subsequently
elaborated by Morgan (1972, 1982, 1985, 1990), Morris (1977,
1994), Cuanne
(1980), La Lumiere (1981), Ellis (1986), Verhaegen (1985,
1987) and Evans
(1981). The nakedness of some aquatic mammals, such as whales,
manatees and dolphins, has been cited as evidence to
support the hypothesis that man may have an aquatic
ancestor (e.g. Hardy, 1960). Nakedness is naturally
advantageous to these aquatic mammals because it
reduces drag and buoyancy (Wheeler, 1985). Once
insulating fur is removed, however, excessive heat
loss is an even greater problem than for terrestrial
species, as water has a higher thermal conductivity
than air (Wheeler, 1985). Most of the diverse
mammalian groups that have adopted an aquatic mode of
life have therefore retained a dense covering of body
hair (Sokolov, 1962; Wheeler, 1985). Most of the
aquatic mammals that have lost their hair have large
and fusiform bodies with small appendages; large
animals possess low thermal conductances, while small
appendages minimize the area of skin in contact with
water (Wheeler, 1985). Furthermore, heat loss from the
extremities is restricted among these mammals by
vascular adaptation, such as heat-exchanging rates at
the base of the flippers (Scholander & Schevill,
1982). Neither of these properties, however, applies to early
hominids; it is therefore difficult to reconcile the
hairless condition of humans with an aquatic existence
(Wheeler, 1985). A naked mammal of the shape and size of
the early hominids or modern humans would have found
maintaining a high body temperature in the sea
energetically very expensive. Even those species of
comparable body mass that inhabit warm tropical
freshwater bodies have retained a thick coat (Wheeler,
1985). There is, furthermore, no fossil evidence to
support the aquatic ape hypothesis, although human fossil
remains are often found near bodies of water (Foley,
1987). It is not very realistic to claim that humans have
ever lived such a totally aquatic life as those marine
mammals that have shed their fur. It is more likely that
our ancestors lived on the shore and caught their food
offshore by wading and diving. Humans would naturally
have returned to the beach to sleep, and would have spent
most of their time ashore. At night, insulating fur would
have been an advantage. ...
_____
Outdated version of AAT (most recent Morgan 1990).
Nobody ever suggested that our ancestors ever lived a
totally aq.life.
Wheeler's papers are irrelevant nonsense here: Accounts of how
our Plio-Pleistocene ancestors may have lived on the savannah
include bouts of strenuous activity outside the gallery forest
for hunting or digging; dogged pursuit of swifter animals over
one or two days; and bipedal trekking after migrating herds of
savannah ungulates. Some of the even more imaginative versions
appear mutually contradictory. For example, the hypothesis of
a foraging or hunting male accords ill with the meridian
theory of Wheeler that our ancestors became bipedal to
minimise direct solar radiation at midday and retained a hairy
heat shield only on top of the head (1984, 1988, in imitation
of DHK Lee in Newman 1970 & in Schmidt-Nielsen 1974:89). If we
accept this reasoning, it must have been the women who ranged
over the plains at noon while the balding and bearded males
rested in the shade.
I'll place the paper in the AAT files within a few days.
--Marc Verhaegen http://groups.yahoo.com/group/AAT
http://users.ugent.be/~mvaneech/outthere.htm
http://users.ugent.be/~mvaneech/Symposium.html