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In this thesis, the following explanation was given for why the majority of people are right handed:

Primitive hunters needed to protect their most vital organ of the body (the heart), so their left hand was used to hold the shield. The right hand was used to hold the sword or knife. Therefore the right hand acquired greater agility, which was passed down through the generations.

Is it true that people are right handed because they had to hold a shield in their left hand in order to protect their heart when hunting?

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Kenshin
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    Are apes "X-handed"? – user5341 Dec 27 '12 at 15:11
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    @DVK: Apparently that question is complicated enough to require an [entire book](http://books.google.com.au/books?hl=en&lr=&id=l2JONnVyGjMC&oi=fnd&pg=PA1&dq=handedness+in+apes&ots=hMnT2Eu2e2&sig=JbTjok4IdzmIe960UDE8aDR3LY0#v=onepage&q=handedness%20in%20apes&f=false) to review the conflicting evidence. – Oddthinking Dec 27 '12 at 22:21
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    I thought shields were used in warfare, not so much hunting…? – Weaver Mar 21 '16 at 09:26

2 Answers2

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The shield-holding idea is not well supported by the references.

Fisher's thesis "Psychosocal differences between left-handed and right-handed children" seems to mainly evaluating consequences not causation. She cites

  • Coates 1996
  • Hollingworth 1923

In the references section these are given as

  • Coates, E.F. (1996). The left handed: "Their sinister" history.
  • Hollingworth L.S. (1923). Special talents and defects, their significance for education.

In fact, the first paper was written by Costas, Elaine Fowler not by Coates. (I've put in a request for this paper)

Other theories about left-handedness claim that left-handers had an advantage in combat. It seems to me that these two ideas are both plausible and yet are contradictory. See Faurie and Raymond.

The location of the human heart is approximately central although it is skewed significantly to the left.

diagram human torso with location of heart diagram human torso with location of heart diagram human torso with location of heart Images from 1 2 3

Any benefit from holding a shield in the left hand is therefore perhaps marginal.

Preliminary conclusion

The selection of handedness is at least partly (but far from wholly) genetic and its origins are not definitively known. No single idea is likely to wholly explain the phenomenon.

Borror0
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RedGrittyBrick
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    Left-handed advantage to combat may be simply because the majority of the enemy are right-handed. If that is the case (that being opposite-handed of your enemy is an advantage), then that probably simply shows that combat has little to no effect on the human evolutionary process. – Flimzy Dec 27 '12 at 09:55
  • Thanks for your preliminary response, +1. I like the use of diagrams in your response. – Kenshin Dec 27 '12 at 10:24
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    @Flimzy : the advantage is not about being opposite-handed of the enemy, but being opposite-handed of the majority, so that a left-handed is used to fight aganist right-handed opponents, but right-handed are not used to fighting aganist opposite-handed. And with sword and shield in particular, the advantage is significative. – Duralumin Dec 27 '12 at 13:40
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    I dislike the image; the heart is in fact [much more central than shown in the image](https://en.wikipedia.org/wiki/File:Surface_anatomy_of_the_heart.png) in most humans. Many schematics simply exaggerate its left-sidedness to make the subtle trend more obvious. – Konrad Rudolph Dec 27 '12 at 21:05
  • @Konrad, I chose a less central version to avoid being accused of unfairly selecting only images that supported my case. Maybe I will add some others for balance. – RedGrittyBrick Dec 27 '12 at 21:21
  • @RedGrittyBrick, thanks for your pictures. Do you think that if the ancients thought the heart was on the left, they would carry the shied on the left and get used to being right handed, and socially pass on this trait, even though the heart is in the middle? – Kenshin Apr 17 '13 at 23:23
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No. Right-handedness appears to be caused by asymmetries in the brain, that arose before humans did. Because of their shared neuroanatomy with humans, most chimps are also right handed.

In a second study, Hopkins and Cantalupo report the first-ever evidence of an association between hand preference and asymmetries in three areas of the brain cortex in chimps. Observing 66 chimps, they correlated asymmetries in brain anatomy with three measures of handedness: Simple reaching (which hand chimps used to pick up a raisin thrown into the cage), two-handed feeding (which hand chimps used to feed themselves chunks of fruit while holding the whole piece, such as a banana, in the other hand), and a measure of coordinated bimanual actions (which hand chimps used to fish peanut butter from a plastic tube with a finger).

Left-handed and right-handed chimps differed relative to the asymmetries in two primary motor areas, the planum temporale and the precentral gyrus. Say the authors, the results “challenge the long-held belief that the neurobiological substrates for handedness are unique to humans.” Just as in humans, neuroanatomy governs whether a chimp becomes a lefty or a righty. Hopkins points out that chimps are also strongly right-handed for manual gestures and throwing, a clue to the origins of more general right-hand dominance in both chimps and humans.” (“Just Like Us: Chimpanzee Brains Are Asymmetrical in Key Areas and Their Handedness Reflects It”, American Psychological Association, December 5, 2004 http://www.apa.org/news/press/releases/2004/12/chimp-brains.aspx )

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    Other mammals (horses, dogs, &c) have 'handedness' or laterality as well, though it tends to be more evenly distributed between left and right. And of course it's harder to notice, since they don't have hands. – jamesqf Mar 20 '16 at 18:23
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    ...and as any football (soccer) player or fan knows, most people are [left or right "footed"](https://en.wikipedia.org/wiki/Footedness) as well as "handed". Right-footedness is also more common than left-footedness, and it's possible to be right-handed but left-footed and vica versa. I'm pretty sure no-one's ever held a shield using their left foot... People also have a [dominant eye](https://en.wikipedia.org/wiki/Ocular_dominance), which is important in activities like archery. Roughly two-thirds of people are right-eyed. – user56reinstatemonica8 Mar 21 '16 at 10:55