On the mirror test and the evolutionary origin of self-awareness in vertebrates.
Masanori Kohda, Shumpei Sogawa, Redouan Bshary
Philosophical transactions of the Royal Society of London. Series B, Biological sciences November 13, 2025 DOI: 10.1098/rstb.2024.0312 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Review Peer reviewed |
|---|---|
| Keywords | False-negatives Mirror self-recognition Photograph self-recognition Self-awareness Shared ancestry hypothesis |
| Key findings | Self-awareness does not require a large brain and may have been present in early shared ancestors of modern vertebrates. |
Abstract
Self-awareness in animals is often documented by showing evidence for mirror self-recognition (MSR), which is confirmed by the mirror mark-test. The classic assumption about self-awareness was that it is a complex cognitive process, restricted at best to a few large-brained species. Indeed, early MSR research yielded positive results only in great apes, elephants, dolphins and magpies, while most endotherm species failed. However, recent detailed proof of MSR based on a mental representation of self, i.e. private self-awareness (PrSA), in cleaner wrasse Labroides dimidiatus, a small-brained ectotherm fish, indicates that the origin and cognitive complexity of self-awareness must be reconsidered. Here, we first recapitulate key concepts on the evolution of self-awareness, and then summarize the evidence that cleaner wrasse exhibit PrSA. We propose that the many negative MSR results are potentially false-negatives, and that self-awareness does not require a large brain. We posit a new hypothesis: self-awareness was already present in the early shared ancestors of modern vertebrates.This article is part of the theme issue 'Evolutionary functions of consciousness'.