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Darwin-L Message Log 2:104 (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.


<2:104>From LANGDON@GANDLF.UINDY.EDU  Wed Oct 20 10:45:45 1993

Date: Wed, 20 Oct 1993 10:45:45 -0500
From: "JOHN LANGDON"  <LANGDON@GANDLF.UINDY.EDU>
To: darwin-l@ukanaix.cc.ukans.edu
Subject: Re: water babies

In message <93Oct20.004643eet.144261-4@utu.fi>  writes:

> Iain Davidson wrote:
> >Elaine Morgan raises some really interesting problems for which her
> >elaboration of the theory seem to offer a plauible explanation, but
> >plausibility is not really enough.
>
> Maybe, but as long as the alternatives are much less plausible, Morgan's
> explanations remain (in my opinion) a better choice for a working
> hypotheses.

Why are the alternatives much less plausible? Are you familiar with 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,
> present or extinct, with the exception of those that are supposed to be our
> immediate ancestors. When non-primate mammals (or birds, for that matter)
> are considered, the "human" 'adaptive character suite' appears in several
> non-related species, and then it must obviously be the result of convergent
> evolution: adaptation of separate evolutionary lineages to shared
> environmental conditions. It just so happens that all these species live in
> aquatic environments.

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.

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.

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.
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. 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? 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?

Bipedalism is not much of an adaptation for aquatic life. Seals and otters are
not bipedal. 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. If you are going to swim in deeper water, why be 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.

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

> JOHN H. LANGDON wrote:
> >There is still enough uncertainty in this date that the strict chronology
> >does not rule out an extremely (phenomonally) rapid aquatic adaptation, but
> >one that effectively discards Australopithecus. However, the aquatic ape
> >model (proposed 1960, developed 1972) makes the most sense under the 1970's
> >and earlier chronology where humans and chimps split 14 Myr. That time scale
> >has since been discarded.
>
> The evolution of humans may indeed be characterized as extremely rapid. Now
> why did humans evolve more rapidly than the other apes? Usually rapid
> evolution is supposed to be connected with rapid environmental changes that
> impose new selection pressures to a species, and that is the standard
> explanation of the savanna hypothesis, too. However, the forest-savanna
> boundary does not seem like a drastical enough environmental change to
> provoke so fundamental morphological and physiological changes as humans
> have, especially since these traits make no sense in the savanna
> environment. An (semi)aquatic phase in human history explains nicely both
> the rapidity of the evolutionary change and the peculiarly marine character
> of those traits that distinguish us from other primates.

What I meant in this comment was that if we had to place the aquatic adaptation
AND its reversal in this narrower time frame (between 7 and 5 Myr), then this
would be impossibly rapid. There was indeed a climatic change in eastern Africa
at the end of the Miocene and into the Pliocene. That very likely correlates
with speciation and rapid evolution of our lineage in the conventional models
for terrestrial evolution. Evolutionary mechanisms, not chronology, make the
aquatic diversion unlikely.

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).

I made a similar reply on the anthro-l list recently. I append it below to
flesh out some of these points.


From: "JOHN LANGDON"  <LANGDON>
Date: Fri, Oct 8, 1993 1:09 PM
To: dhanson@osteon.win.net ANTHRO-L@UBVM.cc.buffalo.edu
Subject: Re: The Aquatic Ape - news (fwd); replies to Douglas Adams please

As a paleoanthropologist, I cannot let this discussion pass by without comment.
The first questions I would ask in critiquing the aquatic theory are:

   What does the aquatic theory explain better that the more conventional
(terrestrial) models?
   Can the individual hypotheses of the aquatic theory be better explained by
conventional models?
   What other predictions/expectations are to be derived from the aquatic
theory? Can these be used to test the theory?
   Is it reasonable in light of our larger understanding of primate and human
evolution and of evolutionary theory?

I suspect that it has been dismissed with little published examination largely
because it fails these questions.

> His guess was that the reason it was not taken seriously was that most of the
> people working in this field were used to looking to the fossil record for
> evidence, and there simply isn't any - but then it is fairly astonishing that
> we have any evidence for anything in the fossil record.

Don't sell the fossil record short. Blanket statements such as this are
commonly found in creationist literature. The fossil record can tell us quite a
bit. For example, the skeletal anatomy of Australopithecus from 3.0 myr is
reasonably well known, even if we are not in agreement on how to interpret it.
The highly fragmentary fossils earlier than that indicate the presence of
Australopithecus afarensis (or at least its teeth) in inland habitats a couple
of million years previously. This narrows the temporal window for the aquatic
phase and its reversal.

> For instance: EM makes much of the fact that man, uniquely amongst
> terrestrial mammals, is bipedal. She argues that there is a very great
> difference  between an anatomical structure which is essentially quadrapedal
> but allows for bipedal locomotion on occasions, and an anatomical structure
> that is exclusively bipedal. She maintains that there is no argument in
> favour of an animal making the huge anatomical changes and sacrifices
> necessary that wouldn't apply equally to many other animals, none of which
> have made that change. (The argument which says that man, uniquely, became
> bipedal in order to carry tools implies that man intended to become
> toolmakers which is obviously ridiculous, but nevertheless seems to slip past
> people's defences with surprising ease.)

[Incidentally, since her first book presented the model in a rather strident
feminist rhetoric, I presume that Morgan would prefer gender-neutral
terminology. Humans, not just men, are bipedal.]

I am in agreement with her criticism of the cultural models for bipedalism. One
cannot comfortably use arguments to explain unique human traits that apply just
as easily to other species. An explanation for human bipedalism must build on
the unique context of our ancestors before bipedalism as we recognize it
evolved, not afterwards.

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).
Humans can and do exploit coastal resources, but I doubt they could have
survived just on those that lie in water shallow enough for us to stand up and
breathe. One would expect that humans adapted for the water would have been as
reliant on swimming as muskrats and otters. I don't find this a convincing
reason for becoming bipedal.

> I looked up bipedalism in the CEHE, but while it went into the mechanism of
> bipedalism in some detail, it passed over the question of how it could
> possibly have arisen rather briefly and vaguely (p79), which surprised me.
> Isn't the evolution of a completely unique and expensive feature like
> bipedalism rather significant?

I think it is significant. I don't want to speak for the CEHE, which I have not
read, but I believe bipedalism to have been one of the first and most
fundamental adaptive shifts which distinguishes the hominid lineage. Is there a
better explanation for it? I think so. As several anthropologists (including
myself) have argued in print, the alternative to human bipedalism is not the
efficient quadrupedalism of most mammals, but the specialized arboreal climbing
anatomy of modern apes, who are not spectacularly efficient on the ground. A
climbing ape committing itself to terrestrialism, would do well to make
whatever anatomical adjustments were necessary to increase its locomotor
efficiency. 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.
Why did our ancestors "choose" bipedalism? Many authors have argued that it was
because of cultural behaviors (e.g. food carrying) that we preferred that
alternative. [This argument is far different from the simplistic model that
says we left an efficient, well-adapted quadrupedal posture for cultural
reasons.] I prefer to consider the possibility that we took the bipedal
alternative by fortuitous chance.

> >EM also makes much of our hairlessness, also an almost unique feature
> amongst terrestrial mammals. How did that arise? I looked in the CEHE but
> there was no entry for 'hair' in the index. I would have thought that the
> evolutionary signicance of hair in the only terrestrial mammal to have
> dispensed with it was worth a mention. So I tried to track the subject down
> by following various other leads from EM's chapter on hair.
> For instance she talks at length about the relative functions of eccrine and
> apocrine glands in other animals and in ourselves. She says that whereas we
> might expected to have apocrine scent and sweat glands all over our bodies
> like our ancestors, ours have atrophied and are only found in limited areas
> of the body. Instead we now sweat dilute salt water from modified eccrine
> glands which other animals use to secret moisture on to their paws to get a
> good grip. Whatever the reason for this change, (and EM, of course, argues
> that it flows directly from our alleged aquatic period) something must have
> caused it. If not an aquatic period, then what? I looked up eccrine and
> apocrine glands in the CEHE and found almost nothing, certainly no sense that
> there was anything here that needed to be investigated or explained. Is EM
> right that our arrangement is highly unusual? If it is highly unusual isn't
> that significant? If it is significant, then what is wrong with the
> consequent arguments made by EM? Maybe a lot - I just can't find out what.
> >The CEHE mentions eccrine glands in the entry about sweat on page 48. It
> >says that our sweating mechanism is particularly effective because it pours
> >copious quantities of weakly saline water on to our skin to cool us down.
> >This means of course that we have to pour copious quantities of water back
> >into ourselves. It doesn't make clear why this profligate expenditure of
> >moisture (which often drips off us before it has a chance to cool us by
> >evaporation) is better for us than the more economical systems used by other
> >terrestrial mammals. The entry states that 'our lack of body hair also
> >ensures that sweat provides very efficient cooling as it evaporates from the
> >heated skin.' If this is true, then why is it that every other terrestrial
> >mammal uses fur as an insulator against both heat and cold, while humans
> >have to wear clothes to cope with either? I wouldn't like to have to wander
> >round the savannah during the day protected only by my sweat glands. Or at
> >night, for that matter. There is no entry in the index for 'clothes'. EM
> >also says that human skin is unusual in having an abundance of subcutaneous
> >fat, which is characteristic of marine rather than terrestrial mammals. From
> >all this she draws a variety of conclusions which support her thesis in a
> >pretty logical and straightforward way. P49 of the CEHE makes the only
> >mention of subcutaneous fat, but doesn't say whether we have more or less of
> >it than other mammals. It notes that 'Fat is particularly beneficial in cold
> >water, because neither fur nor clothing provides significant insulation in
> >these conditions.' It doesn't follow this line of thought anywhere, though,
> >other than to say that successful Channel swimmers are usually the fatter
> >ones.

She is right in describing modern human anatomy. The characteristics she
observed make a consistent picture: Humans are adapted for sustained high
levels of energy expenditure, particularly in hot environments. Sweating
permits us to cool down more efficiently; it also serves as a supplement to the
waste-filtering system of the kidneys. Relying on fat for insulation rather
than hair permits us to bypass that insulation with the bloodstream when
necessary, so that excess heat can be dumped through the skin.
Typical furry mammals in hot climates use their insulation as much to keep body
heat in as to keep solar heat out. This means they have a narrower range of
thermal tolerance and thus a limited ability to shift to high metabolic gear
for very long. Louis Leakey demonstrated this by running some fast savannah
species to exhaustion.
Aquatic species (e.g. hippos) have pursued a strategy resembling ours for a
different reason: water generally penetrates fur and neutralizes its ability to
insulate. Thus fat is better for them.

Clothes were undoubtedly a more recent cultural invention to cope with climates
outside of the tropics. (Even Morgan would have to concede that our ancestors
did not put on bathrobes as soon as they came out of the water.
Yes, there are limits to running around in the tropical sun. People generally
don't-- only mad dogs and Englishmen, as the saying goes.

To me, human skin is reasonably explained. I am investigating parallel
adaptations in other body systems. The aquatic theory offers nothing in this
line that we don't already have.

> So is it the idea that an animal might have been forced into an aquatic
> environment, started to adapt, and was then forced back into a land
> environment?

I happen to find this a very unlikely scenario, given the very narrow time
period allowed for it.

> >The underlying assumption is that the place at which we have arrived is the
> >one towards which we have always been inexorably heading. To think anything
> >else makes us feel insecure of our very existence.
> >The Aquatic Ape Theory, by contrast, gives us picture of a world which
> >happened to tip a few of us into the water and then happened to tip us back
> >out again when we were half-done.

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.

Morgan's other main body of argument comes from reproduction. It also offers no
improvement on conventional models and incorporates some of the same problems.
In short, I fail to see where the aquatic theory has anything to offer that is
better than more conventional ones, and there is no direct evidence in support
of it. She says swimming predisposed us to bipedalism. Isn't it equally likely
that bipedalism predisposed us to swimming?

All of this is not disproof, but it argues that the aquatic hypothesis is
superfluous and unparsimonious. I suggest this is a major reason
anthropologists have generally ignored it. I could go on, but I am out of time.
My class started nine minutes ago.

JOHN H. LANGDON      email LANGDON@GANDLF.UINDY.EDU
DEPARTMENT OF BIOLOGY    FAX  (317) 788-3569
UNIVERSITY OF INDIANAPOLIS   PHONE (317) 788-3447
INDIANAPOLIS, IN 46227

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