The global preference for being right-handed has always interested me. Every now and then you here fluff pieces on the news, especially when they are trying to kill a couple of minutes, about new studies showing “Left handed people are more X” or “Right handed people are less Y” etc. Fun facts to dish out next time you’re in that awkward moment after calling someone the wrong name during sex, but I have often wondered, what about our ancestors?
In western societies today, about 90% of the adult population is said to be right-handed with the remaining 10% consisting of persons variably identified as left-handed, ambidextrous and/or ambiguously handed (McManus, 2002; Soper et al., 1986).
First we should consider what are the fitness advantages of ‘choosing’ a hand? Well, by focussing on one hand we can get significantly better at performing tasks with that hand rather than getting average results with both. So a dominant hand would seem to be of a genetic advantage, however, wouldn’t the ability to switch hands, as the situation requires, also have some benefit?
I found the following study from back in 1977 which addresses the question, emphasis added by me:
"The predominance of the right hand over the left was also reported by Dennis even among Egyptian art forms 3,500 to 4,500 years old, where the ratio of left- to right-handers was 9:111 and 5:100, respectively. However, going further back, Parello, using the "Draw-a-Man Test," found that ancient paleolithic man, from 1,750,000 to 8,000 years B.C., was probably either more ambidextrous or that there was a greater proportion of left-handers than there are now. This is an extremely interesting finding, which fits in very well with evidence from Hole, that the main paleolithic substence economy to 8,000 B.C. was hunting, while agriculture began shortly thereafter. Thus evidence will be presented to show that among the present traditional hunting-fishing population such as the Eskimo, Barry also found a lower degree of conformity on the Asch Conformity Test and more independent values. Hence a higher number of left-handers was predicted for the Eskimo, while observed incidence is 11.3 percent. Conversely, the majority of the agriculturalists of the world since 8,000 B.C., such as the Hong Kong Chinese Hakka, have harsher socialization with very few left-handers (an observed incidence of 1.5 percent).
What this seems to say, although right-handed may have still been dominant in paleothic times, it was much less dominant that it is today, or agrarian cultures.
Another study (full paper available online here) says:
Handedness in the past: Handedness in ancient humans has been inferred by analysis of archaeological samples from skeletons, stone tools and various other artifacts (Llaurens et al., 2009). Several studies indicate that the coexistence of both right and left-handed individuals has been maintained for a long time in hominids. The oldest undisputed evidence is from the middle (ca. 425,000-180,000 YBP) and early upper Pleistocene (upper Pleistocene was 180,000-10,000 YBP), where marking on incisors indicates the existence of Homo neanderthalensis individuals who were right or left handed for sharp tool manipulation while slicing meat held between the front teeth and the other hand (Bermudez de Castro et al., 1988; Lalueza and Frayer, 1997). In the Homo sapiens taxon, indications of handedness polymorphism come from studies of stone artefacts, holemaking rotation movements in wood and wear marks on spoons (e.g., Paleolithic: Keeley (1977) and Westergaard and Suomi (1996); Neolithic: (Faurie and Raymond, 2004). Negative hands painted in caves during the Upper Palaeolithic in Western Europe or more recently elsewhere in the world could also be informative on the handedness of the painter. In all cases, both right and left hands are found with a higher prevalence of left hands, indicating a higher proportion of right-handers for this task (Steele and Uomini, 2005). All the above described studies clearly show a polymorphism of hand use in Hominid populations during prehistoric and historic times with an overall dominance of right-handers. The polymorphism thus seems to have persisted over significant evolutionary time, suggesting that selection may play an important role in the persistence of this diversity (Llaurens et al., 2009).
Aint that something…
Now what about the reasons why we are a species dominated by right-handedness? Well evolutionary theory tells us that natural selection will favour a genetic trait until equilibrium is reached in the environment. The fact that there have always been a similar a number of left-handed people throughout modern history suggests that even though there maybe some negatives in being left handed,there are obviously some positives as well or the distribution would have reached zero. So whatever the physiological reason for some people becoming left-handed and others right, the fact that that genetic variance still exists, proves that there are benefits for both. The above paper elaborates further on this matter.
Overall I believe it would be genetically superior to be truly ambidextrous and have the ability to use both hands just as well as most of us use one. But I concede that our ancestors probably didn’t have the time to train themselves to be ambidextrous, what with all dinosaurs and woolly mammoths chasing them. Whether our caveman ancestors were ambidextrous, I guess is still open for debate, but I don’t see why we couldn’t train ourselves to be…
This morning I brushed my teeth with my left hand (if you want to really feel like an idiot and brush your teeth harder than you ever have, i suggest you try this.) I purposely have been reaching for cups, pens etc. with my left hand. I even moved my computer mouse to the left side. That’s right I am performing an experiment, for 30days I am going to live the left sided life.
Who’s with me?! (crickets)