Abstract
Mirror self-recognition (MSR), investigated in primates and recently in non-primate species, is considered a measure of self-awareness. Nowadays, the only reliable test for investigating MSR potential skills consists in the untrained response to a visual body mark detected using a reflective surface. Here, we report the first evidence of MSR at group level in horses, by facing the weaknesses of methodology present in a previous pilot study. Fourteen horses were used in a 4-phases mirror test (covered mirror, open mirror, invisible mark, visible colored mark). After engaging in a series of contingency behaviors (looking behind the mirror, peek-a-boo, head and tongue movements), our horses used the mirror surface to guide their movements towards their colored cheeks, thus showing that they can recognize themselves in a mirror. The analysis at the group level, which ‘marks’ a turning point in the analytical technique of MSR exploration in non-primate species, showed that horses spent a longer time in scratching their faces when marked with the visible mark compared to the non-visible mark. This finding indicates that horses did not see the non-visible mark and that they did not touch their own face guided by the tactile sensation, suggesting the presence of MSR in horses. Although a heated debate on the binary versus gradualist model in the MSR interpretation exists, recent empirical pieces of evidence, including ours, indicate that MSR is not an all-or-nothing phenomenon that appeared once in phylogeny and that a convergent evolution mechanism can be at the basis of its presence in phylogenetically distant taxa.
Highlights
Since the 1960′s mirror self-recognition (MSR) has been introduced as a measure of the “awareness of self” in great apes and humans (Gallup 1968, 1977a)
The only reliable data informing us of the presence of MSR is the untrained response to a visual body mark detected with the assistance of a reflective surface
Three out of the 14 horses did not shift from social response to contingency behaviors in the presence of the reflective surface
Summary
Since the 1960′s mirror self-recognition (MSR) has been introduced as a measure of the “awareness of self” in great apes and humans (Gallup 1968, 1977a). Other-directed behaviors are elicited by the perception of the presence of a conspecific, while self-directed behaviors involve the investigation of body parts normally not visible without the aid of a reflective surface. In these terms, this shift has been interpreted as a mirror-induced demonstration of self-recognition ability (Suárez and Gallup 1981). The first successful experiments showing the presence of the phenomenon in non-human primates were obtained on Pan and Pongo genera (for an extensive review Anderson and Gallup 2015)
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