Study
Mirror self-recognition in the bottlenose dolphin: A case of cognitive convergence
Reiss, Diana; Marino, Lori
Proceedings of the National Academy of Sciences, 2001
Two dolphins were marked with non-toxic ink on parts of the body they could not see directly, then given access to reflective surfaces. Sham-marking with a water-filled marker controlled for the sensation of being touched.
- Studied in
- Tursiops truncatus
- Sample size
- 2 captive bottlenose dolphins
Both dolphins spent markedly more time at the mirror after real marking than after sham marking, and positioned themselves to bring the marked area into view.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Dolphins show mirror self-recognition, which — given the distance from primates — indicates convergent evolution of the capacity rather than shared ancestry.
How NatureHQ reads it
Two animals is a very small sample, and the mark test is a blunt instrument: passing it is informative, failing it is not, because an animal may simply not care about a mark. The convergence argument is the durable part. Dolphins, elephants, magpies and great apes are not close relatives, and if the capacity has appeared several times independently it is telling us something about what large social brains do rather than about primate ancestry.
- Two individuals, both captive and habituated to humans and to reflective surfaces.
- The mark test cannot be failed informatively — absence of a response is not absence of the capacity.
- Dolphins cannot touch a mark, so the classic self-directed behaviour is unavailable and positioning is used instead.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Proceedings of the National Academy of SciencesPublished in PNAS.
doi.org/10.1073/pnas.101086398
This reference was resolved automatically against Crossref on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-09.