war. These seem to be intended as functionless uses or by-products rather than
true fitness-enhancing, co-opted spandrels. Gould (1991) concluded that among
features of interest to psychologists, such by-products are ‘‘a mountain to the
adaptive molehill’’ (p. 59).
From these arguments, Gould (1991) concluded that the concepts of exapta-
tions and spandrels provide a ‘‘one-line refutation of... an ultra-Darwinian
theory based on adaptation’’ (p. 58). The two standard pillars of evolutionary
biology—natural selection and adaptation—cannot, in principle, account for
human behavior ‘‘without fatal revisions in its basic intent’’ (p. 58). Note that
Gould was not challenging the importance of evolutionary biology for under-
standing human behavior. Indeed, as we show later in this article, under-
standing the nature of the adaptation responsible for producing spandrels (in
this case, the nature of the large human brain) is critical to the analysis. Rather,
he argued that there has been an overreliance on explanation in terms of adap-
tation, and to this important explanatory concept must be added the concept of
exaptation, which is ‘‘a crucial tool for evolutionary psychology’’ (Gould, 1991,
p. 43).
Terminological and Conceptual Confusions in the Invocation of Exaptation and
Adaptation
To apply evolutionary concepts to psychology and to properly evaluate and
contrast the concepts of exaptation and adaptation as potentially critical tools
for evolutionary psychology, several distinctions need to be made, and some
common terminological confusions should be clarified.
Confusion 1: Adaptation versus Intuitions about Psychological Adjustment
Psychologists often use the termadaptiveormaladaptivein a colloquial nonevo-
lutionary sense. Often, these usages refer to notions such as personal happi-
ness, social appropriateness, the ability to adjust to changing conditions, or
other intuitive notions of well-being. It is important to distinguish these collo-
quial uses from the technical evolutionary uses, although evolved mechanisms
may eventually turn out to be important in explaining personal happiness,
well-being, or the ability to adjust to changing conditions (see, e.g., Nesse,
1990).
Confusion 2: Current Utility versus Explanation in Terms of Past Functionality
Taken literally, Gould’s (1991) cited definition of exaptation requires that a
feature be co-opted for its current function and that it now enhances fitness. It
may seem from these phrases that exaptations concern only functions operating
at the present moment, whether or not they operated in the past. However,
evolutionary psychologists and biologists are generally interested in explaining
existing features of organisms. Obviously, a characteristic cannot be explained
by current fitness-enhancing properties that came about after the characteristic
already existed. When evolutionists attempt to explain the existence of a fea-
ture, they must do so by reference to its evolutionary history. All evolutionary
explanations of the existence of species-wide mechanisms are to this extent
explanationsintermsofthepastfitnesseffectsofthatkindofmechanismthat
Adaptations, Exaptations, and Spandrels 649