TORONTO--Watching chimps at play has led one researcher to conclude that humans must have started walking upright before they developed speech. A quadruped's breathing apparatus, according to a report here on 17 June at the American Psychological Society meeting, makes it impossible to talk and run at the same time.
Most laughter research is done on humor, said developmental neuroscientist Robert Provine of the University of Maryland, Baltimore County. But his research focuses on laughter's relationship to social relationships and play. This led Provine to Yerkes Regional Primate Research Center in Atlanta, where he observed what he believes is the evolutionary precursor of human laughter: the "ritualized panting" of chimps during play.
Chimps have to take a separate breath for each gasp, Provine notes, while humans can burst out with a "ha-ha-ha" all in one expiration. He also noted that when quadrupeds run they have to take a breath with every step, which makes it impossible to develop the sophisticated respiratory control necessary for speech. Thus, he says, bipedality, which allowed "the redirection of breathing in the service of soundmaking," enabled humans to evolve speech.
Other researchers have tied bipedality to speech for different reasons. Philip Lieberman of Brown University in Providence, who studies the evolution of the human vocal tract, says Provine's theory fits with his own research. Brain structures that regulate bipedal locomotion are also essential in regulating speech, he says. Thus walking on two legs may have helped shape the brain in a way that was later used for speech and syntax.