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Darwin-L Message Log 2:107 (October 1993)

Academic Discussion on the History and Theory of the Historical Sciences

This is one message from the Archives of Darwin-L (1993–1997), a professional discussion group on the history and theory of the historical sciences.

Note: Additional publications on evolution and the historical sciences by the Darwin-L list owner are available on SSRN.


<2:107>From hantuo@utu.fi  Wed Oct 20 15:02:49 1993

To: Darwin-L@ukanaix.cc.ukans.edu
From: hantuo@utu.fi (Hanna Tuomisto)
Subject: water babies
Date: 	Wed, 20 Oct 1993 22:05:55 +0200

>Why are the alternatives much less plausible? Are you familiar with them?

Yes, I'm familiar with them, I've traced back quite a few of the original
publications. Elaine Morgan has given an excellent answer to why they are
less plausible in her book "The Scars of Evolution. What our bodies tell us
about human origins". But I have not kept an eye on what has been published
during the last two years, so if you (or anyone else) know of any new
papers that are relevant to the topic, I'd be grateful to hear about them.

>> All the traits that are discussed by Morgan are apomorphies of Homo
>> sapiens. At least they are not shared with any other known primate species,
..(stuff deleted)

>I would argue that this is not true. Some of the traits she cites,
>particularly aspects of reproduction which was a major thrust of her first
>book, are not apomorphies. More recent primatology has found that pair
>bonding, estrous/menstrual patterns, extended sexual receptivity (tolerance?),
>etc., do not distinguish humans from other animals.

Sorry for my sloppy usage of terminology here. I was thinking of those
traits Morgan discusses in The Aquatic Ape and in The Scars of Evolution.
Her first book, The Descent of Woman, was not written to advocate the
aquatic theory. It was written to draw attention to the fact that at that
time (sixties-seventies) human evolution was written about as if it were
just male evolution, with females passively following along. It's in the
two last books were she elaborated the aquatic ape theory, and that's where
the sharpest arguments are found. I would like it to be otherwise, but hers
are the only texts I've seen so far that really weight the different
theories on the basis of their scientific merits.

>Many of the list of apomorphies belong to single adaptive complexes that
>require only a single explanation. Rather than considering them independently
>as evidence, they should be lumped.

You said it! This precisely is a very strong argument in favor of the
aquatic hypothesis. Put all the characteristics together that are
apomorphies in humans, and what do you get? The aquatic syndrome, many
traits of which are known from both birds and mammals.

>Evolutionary convergence does not necessarily imply adaptation to the same
>environmental conditions. Convergence with other species, especially distantly
>related ones should be examined carefully and in phylogenetic as well as
>functional context.

Sure, but if phylogeny does not give the answers, you're left with the
environmental explanation.

>For example, reduction of hair, increase in fat, increase in sweating, changes
>in  cutaneous innervation and circulation all relate to a thermoregulation
>strategy. While some of these are paralleled in aquatic animals, others
>(sweating, circulation) do not make sense as aquatic adaptations and are not
>paralleled in aquatic animals.

Humans are not aquatic now, and no one has suggested that they have ever
been fully aquatic. Obviously sweating makes no sense for a fully aquatic
mammal, because there's no evaporation when you're submerged. On the
contrary, there are lots of land mammals that cool themselves by sweating
(e.g. horses), but the difference between them and ourselves is that they
don't waste salts and water. When humans sweat, most of the water does not
even evaporate, it drips off. Someone living close to a permanent source of
salt and water, like a seashore, could afford that kind of a system, but
both substances are difficult to find in the savanna. The only savanna
mammals to my knowledge that sweat as copiously as humans are the hippos,
and they leave the water only at night.

>Replacement of hair with fat was a convergence
>for humans, pigs, and whales as a more efficient solution to heat loss. Whales
>are aquatic. Should we assume that pigs are too?

No.

>Humans and pigs are terrestrial
>and show it by their concern with heat dissipation as well-- pigs wallow and
>humans flush and sweat. Why are whales a better model for humans than pigs?

Whales are NOT a better model. Both animals show equally well the
thermoregulation point: when a mammal lives in an environment that keeps it
wet, it gets rid of its hair and develops subcutaneous fat instead. Whales
are fully aquatic, humans are not. Pigs are mud-dwellers, humans are not.

>Bipedalism is not much of an adaptation for aquatic life. Seals and otters are
>not bipedal.

They did not evolve from primates either, so their bodies did not have the
flexibility that enabled our ancestors to stand up.

>Standing in the water allows you to exploit water up to five feet
>or so in height. (For Lucy, maybe up to four feet.) If you really wanted to
>collect shell fish from water this shallow, wait until the tide goes out like
>clam rakers do.

You may want to go into the water to avoid terrestrial predators, or to
cross a river. You need much less energy for wading if you have most of
your body out of the water. There are two other primates who habitually
wade in a bipedal position: the Japanese macaque and the proboscis monkey.

>If you are going to swim in deeper water, why be bipedal.

In deep water the important thing is not that you're bipedal, but that
you're streamlined. The most streamlined position for a primate is to
stretch the legs backwards parallelly to the spine. Retain that posture
when you go to land, and you become bipedal.

>On the other hand, if you are going to become bipedal, then you may be
>secondarily adapted for swimming (as we are), because both utilize powerful
>lower limbs.

I'd say it went the other way round. Bipedalism is a very difficult way of
walking and has necessitated impressive changes in our anatomy and
physiology. With the support of water, that change could take place
relatively painlessly.

>Are we really well adapted to the water? What other aquatic species looses as
>many of its members in drowning accidents?

What other PRIMATE loses so many in drowning accidents? None, since they
would not play in water like humans do. Except perhaps the Japanese
macaques and the proboscis monkeys.

>Evolutionary mechanisms, not chronology, make the
>aquatic diversion unlikely.

Why?

>If this critique of the aquatic hypothesis is spotty, it is because there are
>so many angles to attack that I hardly know where to begin-- evolutionary
>improbability, the plausibility of conventional models, the lack of parsimony
>of Morgan's model, errors in it (some only apparent in light of more recent
>knowledge).

If you know a more parsimonious theory than Morgan's, please tell me. All
I've seen is a bunch of statements about single characteristics, most of
them contradicting each other. I've never seen a coherent terrestrial
theory. I am very interested in that recent knowledge that shows errors in
the aquatic one.

>Cannot the same criticism be leveled at the aquatic hypothesis? Why are there
>no other bipedal aquatic tetrapods (aside from birds, which don't count).

Why don't they count? The penguins walk on land in a remarkably similar
position than humans do, in spite of the fact that non-aquatic birds have
their spines horizontally when they walk. (I know that geese have their
spines horizontally. But they don't dive, they float.)

>Good monkey-like quadrupedalism is one possibility, but given the tendency for
>upright posture and substantial hindlimb weight-bearing, bipedalism was an
>equally viable strategy.

Except that lifting the spine into a vertical position is a totally new
construction for the entire mammalian lineage. Quadrupedalism could have
been attained by a simple reversal to the original way of locomotion.

>I find the aquatic hypothesis as guilty of this teological thinking as Darwin.
>It focuses entirely on modern anatomy, asking how we got here and ignores the
>really essential consideration of any evolutionary explanation: What did we
>start with and how did that influence our pathway? Nor does she really make
>any use of what we know of the fossil record. The fossils give no hint of any
>such aquatic diversion in the transition from semi-arboreal apes to
>terrestrial humans.

Dear John Langdon:
You cannot have read Morgan's books. She devotes entire chapters to the
fossil record. We seem to be talking about entirely different theories.

Let's make a deal: send out the references to the papers/books that
describe The orthodox Terrestrial Theory, so I can learn what exactly you
are defending. Then you read Morgan's books so you know what I'm defending.
Otherwise we just keep arguing without getting anywhere.

Hanna Tuomisto
hantuo@utu.fi

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