"Just-So Stories"

Critics assert that many hypotheses put forward to explain the adaptive nature of human behavioural traits are "Just-so stories"; neat adaptive explanations for the evolution of given traits that do not rest on any evidence beyond their own internal logic. They allege that evolutionary psychology can predict many, or even all, behaviours for a given situation, including contradictory ones. Therefore many human behaviours will always fit some hypotheses.[citation needed]

For example, kin selection predicts that humans will be altruistic toward relatives in proportion to their relatedness, while reciprocal altruism predicts that we will be altruistic toward people from whom we can expect altruism in the future (but not strangers). A story of any complexity can be constructed to fit any behaviour, but, critics assert, nothing distinguishes one story from another experimentally.[citation needed]

Defenders of evolutionary psychology suggest that the term "just so story" is a derogatory way of describing alternative hypotheses which need empirical evaluation. Furthermore there is no known scientific mechanism which can explain human behaviour besides natural selection.

Leda Cosmides noted in an interview:

"Those who have a professional knowledge of evolutionary biology know that it is not possible to cook up after the fact explanations of just any trait. There are important constraints on evolutionary explanation. More to the point, every decent evolutionary explanation has testable predictions about the design of the trait. For example, the hypothesis that pregnancy sickness is a byproduct of prenatal hormones predicts different patterns of food aversions than the hypothesis that it is an adaptation that evolved to protect the fetus from pathogens and plant toxins in food at the point in embryogenesis when the fetus is most vulnerable - during the first trimester. Evolutionary hypotheses - whether generated to discover a new trait or to explain one that is already known - carry predictions about the nature of that trait. The alternative - having no hypothesis about adaptive function - carries no predictions whatsoever. So which is the more constrained and sober scientific approach?"

In his review article Discovery and Confirmation in Evolutionary Psychology (in The Oxford Handbook of Philosophy of Psychology) Edouard Machery concludes:

"Evolutionary psychology remains a very controversial approach in psychology, maybe because skeptics sometimes have little first-hand knowledge of this field, maybe because the research done by evolutionary psychologists is of uneven quality. However, there is little reason to endorse a principled skepticism toward evolutionary psychology: Although clearly fallible, the discovery heuristics and the strategies of confirmation used by evolutionary psychologists are on a firm grounding."