On the mirror test and the evolutionary origin of self-awareness in vertebrates.
Philosophical transactions of the Royal Society of London. Series B, Biological sciences November 13, 2025 Masanori Kohda, Shumpei Sogawa, Redouan Bshary
Self-awareness in animals, typically assessed via mirror self-recognition (MSR) in the mark test, was long thought to require a large brain and complex cognition, with positive results only in great apes, elephants, dolphins, and magpies. But recent evidence that cleaner wrasse, a small-brained fish, exhibit private self-awareness—a mental representation of self—challenges that view. This review argues that many negative MSR results may be false-negatives, and that self-awareness does not require a large brain. The authors propose that self-awareness was already present in the early shared ancestors of modern vertebrates.