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One historical theory which has been put forward to explain the primacy of right-handedness, is sometimes referred to as the Sword and Shield Theory, and was proposed by the great 19th Century British writer Thomas Carlyle among others. It posits that, in olden times, warriors and soldiers who held a sword in their right hand could better protect their (left-sided) heart with their shield. Right-handed swordsmen, so the theory concludes, therefore thrived at the expense of left-handers. However, the theory ignores the fact that even a shield held in the right-handed could still protect the heart, which is after all reasonably centrally located in the chest. Neither does it explain why all the left-handers have not died out completely over the centuries, nor the evidence of a large right-handed majority long before the days of fighting with swords and shields, nor the purported combat advantage of left-handed fighters (see the section on Handedness and Combat). In addition, as we have seen in the section on Genetic Theories, the heredity of handedness through the ages is far from as simple as this theory implies.
Another history-based theory conjectures that, when one-handed tools like scythes and sickles were first introduced, they were precious objects owned by the community, not by individuals. It was therefore a practical necessity for everyone to share the same handedness in order to be able to use the tools properly and safely, so a bias for one side developed. However, this does not explain why the right side in particular should have been chosen.
Yet another theory suggests that the right side, and particularly movement towards the right, gained great significance as a result of sun worship in prehistoric times. In the Northern Hemisphere, worshippers would face the south or the rising sun in the east and follow the sun from left to right, so that the right became associated with warmth and life. However, this does not explain the right side preference which is also observed in the Southern Hemisphere, nor why the right should have been the side to gain significance, rather than the left side, which is where the Sun came from.
It has been hypothesized that handedness may be a reflection of a person�s innate �turning tendency�, the natural tendency to turn in one direction (usually the right) more than the other. Tests have shown that blindfolded drivers, walker and swimmers actually tend to move in curves, either clockwise or anti-clockwise - with clockwise (to the right) being the more common - while under the impression that they are going straight ahead. Also, it has been shown that people tend to turn more to the right than to the left throughout the course of the day (right-handers turn more to the right and left-handers turn more to the left). However, the theory remains unsatisfactory, as it fails to explain where the turning tendency comes from in the first place.
Finally, in the interests of completeness, mention should also made of an ingenious theory for handedness developed by the Ancient Greek philosopher Plato, which completely lacks credibility but at least suggests that people were thinking about these issues back in 400BC. Plato hypothesized that right-handed mothers and nurses, who carried their child in their left arm so that they could attend to others things with their right, would raise a child that would cling to its mother with its right hand, leaving its left hand free to explore its surrounding and increase in dexterity. According to this theory, a right-handed mother would therefore raise a left-handed child and vice versa, and that left-handed child, if a girl, would presumably reverse the process when it came to her turn to raise a child, so that the proportion of left-handers and right-handers would then switch each generation! However, this is not what we see in practice: although about 83% of right-handed mothers do carry their babies in their left arms, an almost equal percentage (80%) of left-handed mothers do as well, and there is certainly no evidence of generational switching.