A male crouches, sharply drawing his breath to tighten his chest. The cape descending from his neck presses closely against his back. He turns his head upwards, fixing his eyes upon the female.
Suddenly, he puffs his chest, extending it up and out, before returning to his original position. Then, he flips his cape forward, up and over his body, slightly bowing his head. If he's confident that she's interested in his advances, he opens his cape, revealing two reflective blue-green "eye spots" just above his eyes. While holding this posture, he circles slowly around the female. If the female is interested, she takes a slightly submissive stance and turns in place. Their faces nearly touch as she rotates, constantly maintaining eye contact.
The setting for this elaborate courtship ceremony is not some medieval court or Dancing with the Stars. It isn't even a dance club or a crowded bar. This particular ritual takes place in the montane forests of Papua New Guinea. And the participants aren't humans, though they could be. They're superb birds of paradise, Lophorina superba, the cape in this case formed by a splendid plumage of black feathers.
People often suggest dancing as an example of activities that are uniquely human. Many species like the bird of paradise have various sorts of mating rituals, which could be described as "dances" by analogy. But dancing means something more specific: the "rhythmic entrainment to music". In other words, dancing isn't only moving the body in some stereotyped or over-learned fashion. Dancing requires that an individual moves his or her arms, legs, and body in sync with a musical beat. All human cultures ever encountered can do this, and until recently we thought this talent or ability was unique to our species. Until, that is, a celebrity parrot named Snowball knocked us off our place of perceived prominence.
Snowball became famous on the internet when videos were uploaded of the twelve-year-old cockatoo appearing to dance to a Backstreet Boys song. He seems to bob his head up and down in sync with the beat of the song. Sometimes he lifts his feet off his perch, occasionally alternating back and forth between his right and left legs. His crest also seems to raise and lower in rhythm with the music. Could it really be that humans aren't unique in their abilities to dance?
A sceptic might wonder if perhaps Snowball was simply imitating an off-camera human: an impressive ability in its own right, but not good enough to dance with the stars. But a neuroscientist named Aniruddh D. Patel, of The Neurosciences Institute, in San Diego, California, conducted an experiment to find out if Snowball was truly moving to the music, whether his dancing skills were purely the result of anthropomorphism on the part of human YouTube viewers, or whether it was simply imitation.
Patel took one of the tunes that Snowball was familiar with, a Backstreet Boys song called Everybody, and modified it so that the tempo could be sped up or slowed down from 86 to 130 beats per minute, without altering the song's pitch. The researchers took video recordings of the bird's movements while the songs were playing. After analysing their videos, they found that Snowball's dance steps were synchronized to the music. The parrot had moves, after all.
Signs of desire
Was Snowball an oddball, or is dancing widespread elsewhere in the animal kingdom? A second group of researchers ploughed through YouTube in search of data, and wound up with 1,019 uploaded videos that claimed to show non-human animals dancing. After a careful analysis, the researchers were left with evidence of dancing in fifteen species. Fourteen of those were, like Snowball, different kinds of parrot. The fifteenth example was an Asian elephant.
One thing that parrots, humans, and elephants have in common is that they are all vocal learners, meaning they can change the composition of the sounds they make, by changing pitch or the order of a song, for example. The list of species that YouTubers claim can dance is much longer, including ferrets, dogs, horses, pigeons, cats, fish, lizards, snakes, owls, camels, chimpanzees, turtles, ducks, hamsters, penguins, and bears, but they don't pass scientific muster. As domestic species like dogs and horses don't appear have any dancing aptitude, it suggests that this talent doesn't develop entirely from exposure to music. Its origin lies deeper, within the biology of the species.
Human culture has transformed dancing into a form of art, a means of expression. But beneath that scaffolding lies something far more ancient.
Darwin himself noted the apparent similarities between dance rituals in birds and humans in The Descent of Man and Selection in Relation to Sex, writing, "the males sometimes pay their court by dancing, or by fantastic antics performed either on the ground or in the air." He continues, "With birds of paradise a dozen or more full-plumaged males congregate in a tree to hold a dancing-party, as it is called by the natives: and here they fly about, raise their wings, elevate their exquisite plumes, and make them vibrate, and the whole tree seems, as Mr. [Alfred] Wallace remarks, to be filled with waving plumes…One observer, who kept several pairs alive, did not doubt that the display of the male was intended to please the female."
If Darwin was right, and dancing is used as a means for selecting mates – then dancing ability might correlate with the genetic quality of the dancer. In other words, dancing ability might serve as a signal that communicates one's own desirability as a mate. In 2005, William Brown and colleagues from Rutgers University and the University of Washington published a paper in Nature demonstrating that this might indeed be the case.
The researchers used motion capture technology to record people dancing to the same song. They also calculated, for each dancer, the degree to which their bodies were symmetrical. Previous research has indicated that this feature, called fluctuating asymmetry, is related to a person's attractiveness, whether based on odour, voice, or facial appearance. (Note, however, that the use of this measurement is controversial.)
The researchers showed animations, derived from the motion capture process, to 155 people and asked them to rate the dance abilities of the cartoon dancers. They found that males who were more symmetrical were thought of as better dancers than males who were more asymmetrical. (Video samples of symmetrical and asymmetrical dancers can be found here.) Symmetry explained nearly half of the total variation in dance ability for the men.
Symmetrical females were also rated as better dancers than their asymmetrical counterparts, but this only explained less than one quarter of the variation in their dance skills. What this means is that dance ability was a more useful indicator of one's quality as a prospective mate for men than for women, a pattern that would be expected in species where females are thought to be the more selective sex. At least three other research groups have found evidence to support the notion that differences in dance ability among human males reflects some underlying biological or genetic quality, and that females are attentive to those differences.
Both dancing and courtship are, of course, made more complicated and more elaborate thanks to human culture. Strip away that culture, though, and the distinctions among species melt away. When it comes to the birds and the bees, humans might be more like the birds than they realise.