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Mirror, Mirror

Evidence that psychology, like biology, is conserved between human and nonhuman species augurs a shake-up for science and society

G. A. Bradshaw, Robert Sapolsky

Four Square

Science constantly winnows stronger hypotheses from weaker ones by testing them against current knowledge. In making such judgments, a scientist can be right by failing to reject a hypothesis that is true or by rejecting one that is false. Conversely, there are two ways of being wrong: by dismissing a valid hypothesis (what statisticians term a “type I” error) or by embracing an incorrect hypothesis (a “type II” error). With respect to inference, if humans share a trait, such as empathy, with some other animal, then the rejection of that possibility constitutes a type I error, or what primatologist Frans de Waal at Emory University refers to as anthropodenial. At the other end of the spectrum lies the type II error of anthropomorphism, the belief that humans share some trait with another animal when they actually do not.

Evolutionary theory suggests that species with a recent common ancestor are more likely to have traits in common than are distantly related species. Of course, common ancestry does not ensure identity, but as a reflexive stance, neither anthropomorphism nor anthropodenial makes sense. If morphological, physiological and genetic traits merit bidirectional inference, then there is scant reason to exclude mental states. Continuing to do so encourages systematic (and unrecognized) type I errors, thereby adding to a canon of groundless theory.

The obvious gain of a trans-species convention, in which the arrow of inference is independent of species, is consistency in theory and in practice. This dividend pays off in statistical power and subtler perception. As a bonus, such a convention would help scientists from different disciplines, such as ethology and psychology, share theories and speak a common language. But convergence to commonality calls for some additional sorting out.

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