In their basic properties, MNs constitute a relatively simple action–perception mechanism that could have been exploited several times in the course of animal evolution: first as a monitoring system for tracking own behavior, then by functioning as an extended recognition system matching one’s own and other motor representations, and finally for contributing to speech perception and production in humans.86,87
Despite the higher cognitive functions it could serve in some species, the basic mirroring mechanism is very likely much simpler and widespread in the animal kingdom than previously imagined ().
Figure 2 Phylogenetic tree of mirroring mechanisms. Red groups include species where direct evidence of single MNs is available. Orange groups include cases of indirect convergent evidence at both the anatomical and the behavioral level (no recording of single (more ...)
Behavioral and ethological studies have shown that a number of animal species have rich behavioral88
interactions with conspecifics, ranging from body synchronization and mimicry of similar motor patterns to learning action sequences by copying them with high fidelity. Besides primates,90
an astonishing example is provided by the cephalopoda Octopus vulgaris
, which can benefit from the observation of a trained demonstrator performing a motor task to learn to solve the same task more rapidly.96,97
Recent studies indicate that even a non-social reptile, the Red-footed tortoise, shows some forms of behavioral mirroring,98,99
suggesting the possible presence of a “mirror-like” mechanism in this animal.
Until now, direct evidence for MNs has only been available in monkeys, humans, and birds due to technical/methodological difficulties or ethical problems that single neurons recordings involve in many species. Clearly, these limits prevent the reconstruction of a phylogenetic tree of MN systems. However, the behavioral data reviewed here suggest that MNs might have been retained from ancient brain structures, appear to have been well preserved during evolution, and accomplish similar recognition functions, although in different domains and in several species not necessarily closely related to each other.
This would be another one of the many instances57
demonstrating how evolution has shaped not only anatomical, genetic, and developmental traits, but also the underlying neural mechanisms of complex cognitive capacities.