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Aquatic Adaptationists
In 1979, Gould and Lewontin described, and argued against, a
research methodology whose purpose was to explain observable traits
strictly as adaptations and to view natural selection as the primary
agent leading to such traits; they called this methodology the
Adaptationist Program. Gould and Lewontin claimed that under this
program, which dominates evolutionary thinking, researchers assume
that every trait is an adaptation—a trait conferring a survival advantage
and resulting from natural selection—and that they accordingly construct ad hoc or “Just So” explanations for these traits. Other evolutionists, such as Mayr, have attempted to defend adaptive approaches by
pointing out that the supposed flaws described by Gould and Lewontin
actually represent mistakes which no evolutionist with a good understanding of selection and adaptation would make. Gould and Lewontin’s
arguments may thus be based in part on assumptions held only by their
caricatures of adaptationists. While the adaptationist program will
obviously lead to problems with studies, the solution rests not in
abandoning adaptive explanations entirely; rather, it is likely that a
synthesis of these views, one which recognizes the importance of both
adaptive and non-adaptive hypotheses and emphasizes a holistic concept of organisms, will yield the best results.
According to Gould and Lewontin, the adaptationist program is
flawed on several levels. First, it is based on the notion that natural
selection is so powerful that all traits can be explained purely as
adaptations. Studies under this program therefore consist of two stages,
the first of which is to atomize the organism into parts which have been
optimized by selection; once this optimization is proven to be impossible, the investigator attempts to explain traits as tradeoffs between
competing selective pressures. In this way, the program is Panglossian
in nature, as it is based on the concept that animals are optimally
designed, that their bodies are the best of all possible alternatives. The
idea that traits may not be adaptive, however, receives no consideration. Natural selection is seen as so powerful and adaptation as so
universal that researchers blind themselves to the possibility of other,
non-adaptive, explanations. Indeed, if a given adaptive account is
proven false, adherents of this program merely substitute novel adaptive explanations, never stepping back to consider other factors such as
random effects, developmental constraints, or adaptations divorced
from selection. The program, in short, introduces flaws into the
researcher’s framework for developing and testing evolutionary hypotheses.
Other evolutionists, however, reject these criticisms. Mayr argues
that the adaptationist program as defined by Gould and Lewontin
represents a misunderstanding of selection and a faulty implementation
of adaptive explanations. For example, Mayr insists that the concept
of perfection is not a major concern of adaptationists; they do not see
animals as existing in a Panglossian world. Although selection favors
the best of the genotypes at hand, it is not always the best that survive;
random effects can be just as powerful as selection. The practice of
viewing traits as adaptations functions as a heuristic tool, useful in
defining a starting point for study and for giving a framework to
hypotheses and experimentation. It is the misapplication of such a
program, Mayr claims, which is the real danger.
The debate over the adaptationist program has recently been applied to a theory which suggests that certain human characteristics may
be explicable in terms of an aquatic stage in human evolution. The
specific merits or shortcomings of the evidence in question are not at
issue here; suffice it to say that the Aquatic Ape Theory, or AAT, was
originally proposed in the writings of Hardy and Morgan to explain a
number of human traits, including loss of bodily hair, the diving reflex,
the subcutaneous layer of body fat, the eccrine sweat glands, and a host
of features involving the legs, pelvis, and toes. According to Morgan,
all such traits can be explained as adaptations if one assumes that
humans passed through an aquatic stage during their evolution. For
example, the diving reflex would be adaptive if it allowed humans to
plan for and undertake extended dives below the surface, while reduced
hair would be adaptive in that it would facilitate quicker swimming.
The theory was immediately attacked by opponents of the adaptationist
program; Turner, for instance, claimed that the AAT was based on the
assumption that any trait can be explained as an adaptation. This is
precisely the crux of the program’s flaws.
The Aquatic Ape Theory, although derived from a legitimate framework, would seem to represent a misuse of adaptationist methodology.
Even proponents of the adaptationist program recognize the danger
inherent in approaches such as Morgan’s. Under the AAT, Morgan
makes the mistake of atomizing the human organism into a bundle of
traits, hypothesizing that each trait under consideration is discretely
adaptive, and in doing so takes the first step in Gould and Lewontin’s
critical paradigm. It is a mistake to consider that hair loss, fat deposits,
and pelvic structure need all have given humans a selective advantage
and must, therefore, all be adaptations. By breaking up an animal into
discrete pieces and giving these pieces different adaptive explanations,
Morgan loses sight of the holistic sense of the animal. Viewing an
animal as an integrated being which is likely to have parts that have not
resulted directly from selection is a more fruitful course of study. As
Mayr would argue, no good evolutionist, even one working from the
adaptationist program, would neglect the whole animal in favor of its
parts. Morgan fails to look at the human structure in relation to the
evolution of other mammals and does not recognize that humans as a
whole are as well designed for terrestrial life as their individual traits
may seem suited for aquatic life. That humans exhibit adaptations,
many of which may allow them to exploit aquatic resources, should not
cause evolutionists seeking to understand these traits to devise explanations that go against a holistic sense of the animal’s place in the
world. These are the ad hoc stories which opponents of the program
rightly set their sights on.
While it is true that this tendency towards atomization represents
a misuse of adaptive theories, it is not a reason to dismiss adaptation
entirely. An adaptationist approach, if used correctly, gives evolutionists a place from which they can begin to investigate; if a given
adaptive explanation proves to be unsatisfactory, another one, again
based on adaptation via natural selection, may be substituted. Mayr
refers to this as the “dilemma of the adaptationist”: by recognizing the
importance of natural selection and adaptation, the investigator is
forced to consider as many adaptive explanations for a trait as possible
before accepting the possibility that a trait may not be adaptive at all.
This seems to be a reasonable approach—to test several hypotheses,
abandoning those which are not in accord with the facts and moving to
alternatives—so long as it is not used to explain individual traits in a
way that neglects more general facts about an organism. Investigating
traits with the assumption that they are adaptive is like any other
scientific study which starts with a hypothesis and then seeks to prove
or refute it. As long as no pertinent information is neglected, such as
the entire structure or likely evolutionary history of an organism, no
mistake is being made. The AAT may be right or wrong, but the fact
that it is based on viewing traits as adaptations cannot be used to negate
the theory a priori.
Another way to understand this idea is to consider how a nonadaptationist might study the traits Morgan discusses. Alternative approaches, such as those suggested by Gould and Lewontin, might
simply be based on the notion that traits like hairlessness are not
adaptive at all, but resulted from processes other than natural selection.
Possible explanations might be that the trait under consideration is a
consequence of selection acting elsewhere, or that selection is not
acting to produce adaptations. These hypotheses allow for, and in some
cases are explicitly based upon, natural selection; however, they still
allow for the existence of non-adaptive traits or non-adaptive explanations for traits, and, in so doing, sidestep what Gould and Lewontin
regard as the problems with the adaptationist program. In approaching
the AAT, for example, a non-adaptationist may contend that hair loss
is the result of selection on another trait whose effect might be to
reduce the length or density of hair on the body, or that thick, long hair
growth is prevented in humans by developmental constraints. Alternatively, non-adaptationists might point to elements of chance, such as
founders’ effects or bottlenecks, to explain hairlessness: a population
might be reduced to a small number of individuals with little bodily
hair relative to other members of their species, resulting in subsequent
hairless generations. Selection for hair loss need not be occurring at all.
Is the AAT an ad hoc hypothesis, based on the flawed program
described by Gould and Lewontin? In many ways, it is. But this fact
should serve more to emphasize the importance of using an adaptationist
approach correctly than to argue against using this approach as a
heuristic tool. The solution to the debate would seem to lie in a
synthesis of the two sides. An adaptationist, for instance, might make
use of the alternatives suggested by Gould and Lewontin while avoiding the tendency to look at an animal as a collection of unrelated traits;
if tests are done fully and not just acknowledged as an afterthought,
they may actually serve to strengthen an adaptive argument. And if
they are effective, these alternatives should rightly become a part of
every evolutionary study. Opponents of the adaptationist program point
out, quite correctly, that atomizing organisms, suggesting adaptive
explanations for their traits, and then moving from one adaptive explanation to another without considering non-adaptive explanations is not
a good strategy. Proponents of the program, however, are also right in
claiming that looking at traits as adaptive provides distinct hypotheses
which can then be tested. Looking at an animal holistically and then
forming hypotheses about the traits being studied—an approach that
Morgan failed to use—can be done fruitfully from an adaptationist
standpoint. The problem lies in the question of whether evolutionists
are really considering all of the possible explanations.
Works Cited
Gould, S. J., and R. C. Lewontin. “The Spandrels of San Marco and the
Panglossian Paradigm: A Critique of the Adaptationist
Programme.” Proc. Royal Soc. London B 205 (1979): 581–598.
Mayr, E. Towards a New Philosophy of Biology. Cambridge: Harvard
UP, 1988.
Morgan, E. “The Aquatic Hypothesis.” New Scientist 12 Apr. 1984.
. “Sweaty Old Man and the Sea.” New Scientist 21 Mar. 1985.
Turner, A. The Aquatic Ape: Fact or Fiction. London: Souvenir, 1991.