Right, Left, Right, Wrong! An investigation of handedness - some myths, truths, opinions and research

What is Handedness?
Measuring Handedness
Handedness Statistics
Handedness and the Brain
Theories of Handedness ‣
Other Handedness Issues ‣
History of Handedness ‣
Famous Left-Handers ‣
A Few Final Thoughts
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Other Handedness Issues - Handedness and Animals
There is little evidence that other animals, even higher mammals like apes, show any population-level handedness
There is little evidence that other non-humans - even the higher apes, our closest relatives evolutionarily speaking - show any signs of population-level handedness. Although individual animals do tend to have a hand/paw preference (and indeed are remarkably reluctant to switch from their preferred hand in spite of the best efforts of animal experimenters), no preference has been observed at the species or population level, where it appears to remain close to 50% right and 50% left. Researchers have even tried to breed animals according to their paw preference, but the resulting generations still exhibit a random mix. Thus, although the lower animals may show handedness, they do not show right-handedness or left-handedness.

Evidence of Handedness in Animals

During the 1980s, however, some studies started showing some hand preference among chimpanzees, although more so in laboratory studies than in studies in the wild, and many of the results were hotly contested. Some studies showed a right-handed preference of about 60% - significant, but nothing like the level of bias observed in humans.

Bill Hopkins, at the Yerkes Regional Primate Research Center in Atlanta, USA, has made even more contentious claims in recent years, asserting that his captive chimpanzees exhibit a 70% right-handed preference for many tasks requiring manual dexterity, a rate that rises to almost 98% for very specific tasks, like the precise over-arm throwing of objects. However, for everyday food-related tasks (like cracking nuts or digging out honey), the rate remains closer to 50-50.

Some studies have also indicated some hand preference in prosimians (non-ape primates like bush-babies, lemurs, etc, which are considered more primitive in evolutionary terms that either apes or monkeys). Perhaps predictably, the right hand/paw was usually the dominant one, at last for major tasks (the hand used to grasp a branch after a leap, for example), although the left was definitely preferred for quick small movements like catching insects.

In the same way as we humans can open a door with either hand equally, yet struggle to write legibly with our non-dominant hand, the complexity of the task appears to be an important factor in the handedness of animals. Most lower order animals do not engage is many activities requiring significant levels of dexterity, but when they do, some evidence of a preferred handedness may emerge. A small study at Queen's University Belfast suggests that cats exhibit quite strong laterality preferences when engaged in sufficiently dextrous tasks, such as extracting food from a small jar. Interestingly, a distinct gender bias also emerged, with 95% of females favouring the right paw and 95% of males favouring the left for such tasks. For simpler tasks, the same cats used their right and left paws about equally.

It is still generally accepted that the lower animals do not exhibit anything like the same strength of hand preference as humans, but the waters continue to be muddied as new studies yield new and interesting results. For instance, it appears that some other animals that rely on the production and analysis of complex sounds, including whales and songbirds, also show evidence of lateralized brains. According to one study, humpback whales have also been seen to exhibit a 75% predilection for slapping their right flukes on the water surface. Some other aspects of laterality, particularly of the eyes, have also been observed in many lower animals, from toads to birds to fish.

Animal Handedness Myths

Many websites are fond of claiming that all polar bears are left-handed, but this turns out to be yet another left-handedness myth: in fact, they show a 50-50 paw preference, with perhaps a slight preference for the right according to one study. Another popular myth is that all horses are left-handed/hoofed. Horses are traditionally led and mounted from the left side and trained to turn to the left, and some people insist that this is in order to take advantage of a natural left-handed, left-turning instinct. Recent research reported in Applied Animal Behaviour Science, though, showed that about 53% of horses prefer to lead with the right leg, 40% with the left and 7% showed no preference.

In fact, the only other animal which has shown a distinct population-level left-handedness bias (and indeed the only animal exhibiting handedness at anything like the same level as humans) turns out to be the parrot, with 90% of parrots favouring the left-foot for picking things up in one major study.


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Introduction | What is Handedness? | Measuring Handedness | Handedness Statistics | Handedness and the Brain | Theories of Handedness | Other Handedness Issues | History of Handedness | Famous Left-Handers | A Few Final Thoughts | Sources
© 2012 Luke Mastin