Monday, May 1, 2017

Synchrony, Dance, and Cultural Evolution

Kevin Laland has an interesting article on cultural evolution over at This View of Life, "Darwin’s Unfinished Symphony: How Culture Made the Human Mind". I'm not going to try to summarize it beyond noting that he comes to focus on dance as an example, arguing that dance is necessarily learned through imitation and that the tricky aspect of imitation is what he calls the correspondence problem. What's the correspondence between movements you observe in others and the actions you must take so that your movements imitate them? Your observations consist of visual information, but your actions are motor and kinesthetic.

Here's a passage that speaks to my hobby horse, synchronization:
This ability to move in rhythmic synchrony with a musical beat by nodding our head or tapping our feet, for instance, is a universal characteristic of humans,[42] but is rarely observed in other species.[43] The most prominent explanation for why this should be, known as the “vocal learning and rhythmic synchronization” hypothesis,[44] is broadly in accord with the arguments presented here.[45] This hypothesis suggests that moving in time to the rhythm (known as “entrainment”) relies on the neural circuitry for complex vocal learning; it is an ability that requires a tight link between auditory and motor circuits in the brain.[46] The hypothesis predicts that only species of animal capable of vocal imitation, such as humans, parrots and songbirds, cetaceans, and pinnipeds, but not nonhuman primates and not those birds that do not learn their songs, will be capable of synchronizing movements to music. [...]

Thus far, evidence for spontaneous motor entrainment to music has been reported in at least nine species of birds including several types of parrot, and the Asian elephant, all of whom are vocal imitators,[51] and several of which show motor imitation.[52] Entrainment has also been shown in a chimpanzee,[53] a renowned motor imitator.[54] The sole exception to this association is the California sea lion,[55] which is not known to exhibit vocal learning. However, the fact that related species show vocal learning, including several seals and the walrus,[56] raises the possibility that this capability or a relevant precursor may yet be demonstrated. Lyrebirds have not been subject to entrainment experiments, but males are famous for their ability to imitate virtually any sounds, including dog barks, chainsaws, and car alarms. They can match subsets of songs from their extensive vocal repertoire with tail, wing, and leg movements to devise their own “dance” choreography.[57] Clearly, there is more to dance, at least social or collective dance, than entrainment to music. There must also be coordination with others’ movements, which would seemingly draw on the neural circuitry that underlies motor, rather than vocal, imitation.[58] However, a recent analysis of the avian brain suggests that vocal learning evolved through exploitation of pre-existing motor pathways,[59] implying that vocal and motor imitation are reliant on similar circuitry. The animal data provide compelling support for a causal link between the capabilities for imitation and dance. Whether this is because imitation is necessary for entrainment, or merely facilitates it through reinforcing relevant neural circuitry, remains to be established.

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