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Darwin-L Message Log 2:102 (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.


<2:102>From hantuo@utu.fi  Tue Oct 19 17:43:12 1993

To: Darwin-L@ukanaix.cc.ukans.edu
From: hantuo@utu.fi (Hanna Tuomisto)
Subject: water babies
Date: 	Wed, 20 Oct 1993 00:46:41 +0200

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.

P.E. Griffiths wrote:
>Morgan's argument for the aquatic ape hypothesis is typical of a class of
>adaptationist arguments which try to increase the plausibility of an
>hypothesised adaptive phase by listing a large number of traits which it
>can simultaneously explain. It does this quite impressively.

>Bob O'Hara (1988) has drawn attention to the dangers of giving adaptive
>explanations of character states without paying attention to the cladistic
>relationships of those states.

>In this particular case, the argument falls down unless the proposed
>'adaptive character suite' emerges in the same general area of the tree for
>primate lineages. If, instead, it is a collage of traits from different
>portions of the tree then it cannot be a response to a single adaptive
>phase.

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.

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.

Hanna Tuomisto
Department of Biology
University of Turku
FIN-20500 Turku, FINLAND

Phone +358-21-6335634
Fax   +358-21-6335564
e-mail  hantuo@utu.fi

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