“A prominent British psychiatrist recently revived old arguments about the origins of language and the evolution of humans. Tim Crow at Warneford Hospital in Oxford says that reports on ape brain asymmetry are distorted by observer bias. Those criticized point to ‘plenty of evidence’ that general functions and skills have gravitated to one side of the brain or the other in animals from chicks to chimps.
Crow argues that researchers are finding evidence of language precursors in apes because they want to believe in a graduated theory of evolution, rather than the leap proposed by Thomas Huxley, Stephen J. Gould, and others. Crow points to studies that have reanalyzed data and found no support for initial conclusions of asymmetry. He also asserts his support for the model proposed by neuropsychologist Marian Annett in 2002, in which she suggests that a single gene gave rise to language in the brain’s left hemisphere, and brought a shift towards right-handedness.
In 1877, Paul Broca argued that brain asymmetry distinguishes humans from other animals and gives humans the capacity for language. Then scientists started finding evidence of asymmetry in other vertebrates. ‘Many of the lateralized functions of the human are the same as those in animals,’ says Lesley Rogers of the University of New England in Australia, who with Richard Andrew coauthored the 2002 book Comparative Vertebrate Lateralization. ‘Language has a left-hemisphere location in most humans. It might rely on the evolution of some nuance of laterality, but the point is, it was superimposed on other lateralities that were already there.’
Rogers and Andrew offer examples, such as the left-footedness of parrots, the right-hand preference of toads, and the reliance of chicks on the right hemisphere for spatial cognition. Songbirds show strong lateralization for song production. But when it comes to the great apes, Rogers admits, the evidence for handedness is more controversial. Chimps at the Gombe National Park in Tanzania, for instance, showed no evidence of right- or left-hand preference at a population level according to a 1996 study.
Even in humans, says Richard Palmer at the University of Alberta, Canada, nobody really knows why handedness exists or whether it has a genetic basis. ‘The amount that we know with confidence about human handedness is so pitiful it’s almost shocking,’ he says. Indeed, no one has ever demonstrated a causal link between handedness and language.” —The Scientist
