Dance, dance evolution

It’s not often that YouTube spurs a scientific breakthrough, but that’s what happened when Aniruddh Patel, PhD, saw a video of Snowball, a sulphur-crested cockatoo, stepping side to side on the back of an armchair, bobbing his head and kicking his feet in time to “Everybody,” by the Backstreet Boys.

YouTube abounds with amusing animal videos, but this one was special, says Patel, a researcher at the Neurosciences Institute in San Diego. Scientists have long thought that only humans have the ability to move in time with music. Our closest genetic cousins, chimps, don’t move to music. Neither do dogs or cats, even though they’ve lived and evolved alongside humans for millennia.

“I thought it was remarkable, so I contacted the owner, and we ran an experiment,” says Patel.

His resulting paper, published in Current Biology (Vol. 19, No. 1), showed that Snowball moved in time with music, adjusting his pace when researchers slowed down or sped up the song. That’s an important finding, says Ahalya Hejmadi, PhD, a psychology professor at the University of Maryland University College, and it’s among a new wave of dance research that is helping scientists understand the way the brain coordinates movement. Such dance research could even lead to new therapies for people with movement disorders, adds Patel, noting that some people with Parkinson’s disease who generally can’t move at all can walk in time to music.

At the same time, dance research is giving us insight into a ubiquitous human phenomenon. Scientists are finding that an activity that probably started as an accident of evolution has become an important cultural force, one that gives us insight into selecting mates and tools for fostering cooperation.

“Dance is such a universal phenomenon,” says Hejmadi. “People all over the world love to dance, so there must be some reason for it.”

Bird and human brains

Twenty-somethings gyrate in clubs, ballet dancers rise up on tiptoe, revelers circle around a bride and groom — people around the world dance in many ways for many reasons. However, Snowball the cockatoo suggests that the basic capacity that underpins all this dancing, the ability to move in time with music, is probably just a happy accident of evolution.

The reason that cockatoos and humans can dance, while monkeys and dogs can’t, theorizes Patel, is that we are vocal learners. That is, we hear sounds and mimic them — a skill that requires close connections between our auditory and motor circuits.

“Dance requires a brain that’s been wired up to reproduce complex sounds,” says Patel. “It’s a very rare ability in nature — dolphins do it, seals do it and songbirds do it, but the vast majority of species don’t do it, including most primates.”

To investigate this idea, Harvard psychology student Adena Schachner and her colleagues realized that they needed far more data than typical experiments could provide. “To show that only vocal learners move to a beat, we need to show that non-learners can never do it,” Schachner says. So, they turned to YouTube, with its thousands of animal video clips from around the world. After systematically searching the database, they found more than 5,000 videos that supported Patel’s hypothesis. Only 33 of those showed animals moving in synch with music — 32 birds and one elephant — according to the study, published in Current Biology (Vol. 19, No. 1).

The dancing birds in the study were parrots, macaws and cockatoos — well-established vocal learners. The elephant, however, is a bit of a mystery, says Schachner. Researchers have not yet determined that elephants are vocal mimics. In addition, scientists haven’t observed an elephant spontaneously move in time to music, so You Tube’s “dancing” elephant could be the result of trainer trickery, such as adjusting a song’s tempo to match an elephant’s movement.

“The parrot owners say things like, ‘I don’t even know how to train animals — this parrot just started dancing one day when we had the music on,’” says Schachner. “We haven’t been able to reach the elephant owner.”

It’s striking, says Schachner, that despite the many cat and dog “dancing” videos, and strenuous efforts by trainers to teach these animals to dance, not one out of hundreds of YouTube videos showed one moving in time to a beat. In contrast, the vocal mimics seem to dance naturally, even though they have no apparent use for this skill in the wild.

“It seems that part of dance emerged as a byproduct of our ability to imitate sound,” she says. “Without vocal imitation, we wouldn’t be able to keep to a beat.”

Patel’s theory — that close ties between the brain’s motor system and the auditory cortex underpin our ability to dance — builds on research by Duke University neuroscientist Erich Jarvis, PhD. He has argued that birds and humans have similar brain wiring that allows them to mimic sound, and theorizes that the basal ganglia — a deep brain structure involved in motor control — is important to vocal learning. That’s a crucial connection because brain imaging research on humans has shown that activity in the basal ganglia becomes stronger and more tightly coupled to the auditory cortex when people hear music with a beat, even if they don’t move in time, Patel says.

“If humans and birds are wired up for vocal learning in similar ways, then comparative work with birds could be useful for studying the neuroscience of how we move to music, including the beneficial effects of rhythmic music for people with Parkinson’s disease,” says Patel.

Dancing for the ladies

Clinical applications are a long way off, but dance research is giving scientists insight into the purpose of this human phenomenon. After all, people around the world and throughout history have elaborated greatly on that ancient impulse to move to a beat. But while the whole-body convulsions of African folk dancers seem so different from the stiff posture of Irish dancers, these and many other cultures often use dance within their courtship and mating rituals, says William Michael Brown, PhD, a psychologist and dance researcher at Queen Mary University of London and the University of East London

“In Western societies, we go to nightclubs and dance, and it seems very much linked to sex,” he says.

In particular, people may use dance to spot genetically robust mates, according to research by Brown, published in Nature (Vol. 438, No. 2). In the study, Brown and his colleagues used motion-capture technology to record the movements of 40 Jamaican men and women as they danced to a popular song. The researchers reduced the dancers to stick figures to remove any cues about the dancers’ bodies and attractiveness.

Then, a different group of 155 Jamaicans watched the dances, and they greatly preferred the dances of people with symmetrical bodies. Women judged the dances by asymmetrical men particularly harshly, says Brown. Asymmetrical men, he says, tended to be more lenient, sometimes even preferring the dances of asymmetrical women. Perhaps, says Brown, men who know they are not attractive lower their standards for female dancers, thus increasing their chance to mate. Asymmetrical women may keep their standard high because a bad mating is more costly for women, who invest nine months in gestation and then tend to take on the bulk of child-rearing responsibilities.

But even to a casual viewer, the symmetrical dancers seem more skilled, Brown adds.

“Their movements are smooth; they appear designed for efficiency,” he says.

Past research suggests that people and other animals prefer symmetrical mates, and scientists believe this is because small differences in the two halves of the body reveal developmental snafus, disease and perhaps even defective genes. However, without whipping out a ruler on a date, it’s pretty tough to tell whether a person’s left ear is a millimeter longer than the right. So perhaps we use dance to make asymmetries — and the developmental and genetic problems they indicate — more apparent, says Brown.

“Asymmetry could go hand in hand with balance and coordination problems, and those are pretty hard to conceal when you’re dancing,” he says. However, even inept dancers are expected to play the game. In Jamaican culture, and in the mating dances of many animals, it’s better to be a bad dancer than a nondancer, Brown says.

In addition to preferring the dances of symmetrical men, women also prefer the dances of stronger men and those who had high exposure to testosterone in the womb, according to research by Bernhard Fink, PhD, a psychology professor at the University of Goettingen, in Germany. In a study, published in Personality and Individual Differences (Vol. 42, No. 1), Fink and his colleagues blurred videos of 12 male dancers and had a panel of 104 women rate their attractiveness. The women significantly preferred the dances performed by men with a low second-to-fourth-finger ratio — a reliable indicator of early testosterone exposure. In a similar study by Fink, published in Personality and Individual Differences (Vol. 47, No. 1), men who did well on a handgrip strength test also danced well, at least in the eyes of female viewers.

“Like with physical characteristics, we believe that dance conveys information about an individual’s quality, which may be used by men and women in their mating decisions,” Fink says.

Both Fink and Brown are investigating what it is about these testosterone-fueled, symmetrical, strong men’s dances that make them so attractive to women. Brown even strapped accelerometers onto good and bad dancers, to measure how fast they move and estimate how many calories they burn while doing it. Preliminary data suggest that good dancers cover more ground without burning as much energy.

“Moving efficiently would definitely have survival and mating benefits,” he says.

Cultural customs

Dance doesn’t just help you attract a mate, it also may help you keep one. Swans, for example, paddle circles around lakes in perfect sync with their mates, a movement that seems to deter potential interlopers, says Brown. The same may be true for humans.

Couples dancing together in tightly coordinated ways signal that they are highly bonded and committed to one another, he says. “So committed that you don’t have a chance to get with this person, no matter how good-looking you are,” he adds.

A pilot study by Brown showed that couples can transmit this signal by simply holding hands and walking in a circle — the foundation for a variety of partner dances. A group of undergraduates who watched stick-figure versions of the couples could easily tell which ones were in a romantic relationship and which were strangers.

Dancing in sync with other people also seems to foster feelings of group affiliation, says Scott Wiltermuth, PhD, an organizational behavior professor at the University of Southern California. In a study published in Psychological Science (Vol. 20, No. 1), Wiltermuth and his colleague Chip Heath, PhD, asked groups of students to walk around campus together, some marching in step, while others walked normally. He then brought the groups back to his lab and had each person secretly select a number between one and seven. The group members were told that whoever chose the lowest number received the most money, and that number set the payout for the rest of the group. Therefore, it made sense to select a high number for the good of the group, though selecting a low number ensured the greatest chance of a decent individual payout.

Wiltermuth found that people who had walked in step around campus tended to choose higher numbers, on average, than the control group. They also reported greater feelings of connection with their group members.

“There is something about doing the same thing at the same time with other people that really bonds us and expands our sense of self,” he says. “We come to think of the group as part of us.”

That feeling can be fostered by something as simple as tapping in time with other people, according to research published in Social Cognition (Vol. 27, No. 2). In the study, people who tapped in time with an experimenter felt closer to that person than participants who tapped out of time with the experimenter or alone.

“Synchrony seems to blur the distinction between self and other,” says study author Michael Hove, PhD, a psychologist at the Max Planck Institute for Human and Cognitive Brain Sciences, in Germany.

Cultures, companies and armies have long capitalized on this phenomenon, adds Brown. Japanese corporations, for example, often have employees do calisthenics together in the morning to boost feelings of group membership. That’s probably the same reason armies teach new recruits to march in step. It’s certainly not for practical reasons, says Brown, as marching into war has been a terrible and possibly suicidal tactic since the advent of machine guns.

In fact, anthropologists have observed that many folk dances are large, group numbers. In addition to giving strong dancers the opportunity to showcase their good genes, these rituals enhance everyday cooperation and possibly even helped lay the foundation for human civilization.

“Perhaps it’s no accident that communities come together through dancing,” Brown says.