When the dogs looked at an aggressive, unfamiliar dog — a large Belgian shepherd Malinois — their tails all wagged with a bias to the left side of their bodies.
Thus when dogs were attracted to something, including a benign, approachable cat, their tails wagged right, and when they were fearful, their tails went left, Vallortigara said. It suggests that the muscles in the right side of the tail reflect positive emotions while the muscles in the left side express negative ones.
While some researchers have argued that only humans show brain asymmetry — based on the evolution of language in the left brain — strong left and right biases are showing up in the brains of many so-called simpler creatures, said Lesley Rogers, a neuroscientist who studies brain asymmetry at the University of New England in Armidale, Australia.
Honeybees learn better when using their right antenna, she said. Male chameleons show more aggression, reflected as changes in body color, when they look at another chameleon with their left eye. A toad is more likely to jump away when a predator is introduced to its left visual field (right brain/fear). The same toad prefers to flick its tongue to the right side when lashing out at a cricket (left brain/nourishment).
Chimpanzee brains are asymmetrical in the same ways as human brains, said William D. Hopkins, a researcher at the Yerkes National Primate Center and psychologist at Agnes Scott College in Atlanta. When chimps are excited, they tend to scratch themselves on the left side of their bodies, reflecting strong negative emotions, he said. And left-handed chimps are more fearful of novel stimuli than right-handers. Their dominant right brains may make them more cautious.
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