I attended the Physics lecture yesterday at UCL, given by Professor Chris McManus from the UCL Faculty of Life & Medical Sciences.
9.9% of people in the world are left-handers. 11.6% of guys and 8.6% of girls are left-handers, so for every 4 female lefties, there are 5 male lefties. One famous left-hander is Obama, both writing and throwing balls with his left hand. 30% of lefties and just 2% of righties throw balls with their ‘opposite’ hand.
Pierre Curie, husband of Marie Curie, who discovered rubidium, developed the Curie Principal. In 1894, Curie said that “When certain effects show a certain asymmetry, this asymmetry must be found in the causes which gave rise to them.” This confused most of us, so we were kinda relieved when we were introduced to another quote by a guy called Japp in 1898, which made more sense: “Only asymmetry begets asymmetry.”
Simplicity can be symmetric, and complexity begets asymmetry. For example, hobby horses, which were like the skateboards of the 1810s, and the penny farthing, were symmetrical. When safety bicycles, the bikes of today, were introduced, bicycles became asymmetric. The gears always go on the right side, and brakes differ from country to country. The brakes on the left are for the back wheel in Britain, whereas the brakes on the right are for the back wheel in France.
There’s quite a lot of symbolism linked to left and right. When asked, most people will say that left is bad and right is good. Robert Hertz found that in every society that he studied, the right hand side is always good. In a church in Assisi, Italy, the left hand side fresco shows the Old Testament, and has symbols linked to the devil, evil, women, and secular symbols. The right hand side fresco shows the New Testament, and spiritual and righteous symbols. Furthermore, no society has more left handed people than right handed people.
So why are most people right handed? Plato’s theory was that “it is due to the folly of nurses and mothers” that we are the way we are. Aristotle argued that “the right hand is… superior to the left… by natural distinction”. The former was wrong, and the latter was correct. This led on to the question of nature versus nurture. When in life does handedness develop? It was found that most foetuses suck their right thumb, and most that sucked their right thumb became right handed when they were five years old. Studying stone tools have shown that humans have been right-handed for about 2-3 million years.
Humans are 90% right-handed, so what about animals? Experiments have found that animals are 50% left-handed and 50% right-handed. It seems that asymmetry arises as organisms become more complex. In all animals, the right hand is controlled by the left half of the brain. We have asymmetric bodies. We may look symmetric on the outside, but that’s where the symmetry ends. Our hearts are on the left hand side, but 1 in 10,000 people have Situs inversus, a condition where the heart is on the right hand side. Insects in Eric Carle’s Animals Animals are depicted to have their hearts on the left hand side. In actual fact, their hearts are bang in the middle.
Louis Pasteur, a French chemist, found that biological molecules are asymmetrical. Living organisms are almost entirely composed of L-amino acids. Humans are made up of, among other things, D-sugars and L-valine. Most amino acids on Earth are left handed, because once life started using L-amino acids, it could only continue that way. Meteorites contain amino acids and many other organic molecules. Carl Sagan and others calculated that it took 300 million years to provide all the amino acids on Earth. The amino acids in meteorites were predominantly left handed.
I hope that explains a bit about left and right handedness. I apologise for any mistakes that may have cropped up.