Study
Exaptation — a missing term in the science of form
Gould, Stephen Jay; Vrba, Elisabeth S.
Paleobiology, 1982
Proposes a term for a feature that is currently useful for something other than what selection originally built it for, distinguishing it from an adaptation in the strict historical sense.
- Studied in
- Animalia
- Sample size
- conceptual paper
Current utility and evolutionary origin are separate questions, and a large fraction of useful traits were co-opted rather than built for the job they now do.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
The vocabulary of adaptation needs a term for co-option, because without one every useful feature gets described as though selection produced it for its present use.
How NatureHQ reads it
Cited on the survival pages because so many extreme-tolerance mechanisms are co-options. The proteins that let a tardigrade dry out, the sugars that protect a frozen frog, the haemoglobin variants of high-altitude birds — several of these have ordinary jobs elsewhere and were recruited, which is a different story from being built for the extreme.
- Conceptual rather than empirical, and distinguishing an adaptation from an exaptation for any given trait requires historical evidence that is often unavailable.
- The terminology is not universally adopted.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Adaptation
Finding that a feature helps an animal survive somewhere does not show that it evolved for that. It may be a by-product, a leftover, or something built for another job entirely and later put to this one.
Antifreeze proteins
The antifreeze protein of Antarctic fish evolved from a digestive enzyme gene. Parts of the original are still legible in the sequence — a survival mechanism that was recruited rather than invented.
High-altitude adaptation
The Tibetan altitude variant came from Denisovans, inherited from another human lineage and then selected for. It damps the usual low-oxygen response rather than amplifying it.
Venom
Venom was not built from nothing. The same handful of protein families — digestive enzymes, immune proteins, signalling peptides — have been recruited into venom independently in many unrelated lineages.
Published by: University press journalsPublished in a university press journal.
doi.org/10.1017/s0094837300004310
Checked against Crossref on 2026-09-28, and they agree on the title, the authors and the year.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-09-03.