Many evolutionary explanations are convincing because they make intuitive sense. But when can we say that a trait is truly an adaptation?

Consider the tendency to err on the side of caution – to interpret ambiguous signals as threats. A common evolutionary explanation runs as follows: organisms that avoided potential danger were more likely to survive, so natural selection must have shaped this tendency. But how precise is this claim?

Is this bias itself a specific adaptation shaped by natural selection? Or is it simply a feature that is useful today, but not directly selected for in our evolutionary past? The answer may turn out to be more layered than this question suggests. To begin examining this this, we need to distinguish between two concepts: adaptation and adaptive property.

An adaptation is a trait that evolved through natural selection because it increased survival or reproductive success in a specific environment. It is not only useful – it has a history of selection and is heritable.

An adaptive property, by contrast, is simply a trait that is useful in the present. It may increase fitness today, but it does not have to be the result of direct selection for that function.

This distinction matters. Reading, for example, is highly useful in modern societies. But it is not an adaptation. It relies on cognitive capacities that evolved for other purposes. By contrast, other traits may be genuine adaptations even if they no longer serve a clear function today. Confusing these two categories – treating every useful trait as if it were shaped by natural selection – is one of the most common problems in evolutionary explanations.

Returning to the example of threat perception, the question becomes more precise:

Is the tendency to favor false alarms a specific adaptation – a single trait shaped by selection for a particular function? Or is it a general design principle – a recurring pattern that selection produces in any decision system where the costs of errors are asymmetric? And if so, could we use this idea for identifying actual adaptations?

At this stage, we cannot yet answer this question, and the answer may turn out to be more layered than a simple yes or no. But we now have a first tool to examine it more carefully.

Reflect

Consider the tendency to interpret ambiguous signals as threats. Is it a specific adaptation, an adaptive property, or perhaps something that does not fit neatly into either category? What would you need to know in order to justify your answer?

Author: Fabian Müller

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References

Alberch, P. (1982). Developmental constraints in evolutionary processes. In J.T. Bonner (Ed.), Evolution and Development. Springer.

Amundson, R. (1994). Two concepts of constraint: Adaptationism and the challenge from developmental biology. Philosophy of Science, 61(4), 556–578.

Gould, S. J., & Lewontin, R. C. (1979). The spandrels of San Marco and the Panglossian paradigm: A critique of the adaptationist programme. Proceedings of the Royal Society of London B, 205(1161), 581–598.

Mayr, E. (2005). Das ist Evolution. München: Goldmann.

Richardson, R. C. (2007). Evolutionary Psychology as Maladapted Psychology. MIT Press.

Scholl, R. (2015). Vorlesung: Philosophie der Biologie (Herbstsemester 2015, Universität Bern).