15. The evolution of hand
Animals' front feet and rear feet are similar. However, human being's hands and feet are clearly different. Fingers are longer than toes, and the thumb can be rotated 90 degrees, so it makes it easier to hold things. It becomes clear that thumb can be rotated 90 degrees when you clench your fist. Reversely, toes are shorter, and the great toe cannot be rotated, so it is hard to grab things. To summarize, if you compare hands and feet, you can see how hands have evolved.
Skin of palm and sole is the thickest among human body. Also at the center of palm and sole, there is a thick aponeurosis. Thick skin and aponeurosis protects muscle, nerves, and blood vessels in palm and sole. This is reasonable, since remote ancestors of human beings crawled. Due to thick skin and aponeurosis, it is hard to pinch the center of palm and sole. "You can easily find out that one's palm is harder to pinch compared to the dorsum of hand."
Between the skin and aponeurosis of palm, there is subcutaneous tissue which is made of fat. However, there is a place where subcutaneous tissue is not present. At this place, the skin touches aponeurosis so it is caved in, and that location is the palm crease. Due to palm creases, one can easily bend the thick skin of the palm, and thus one can easily bend one¡¯s fingers. To put it concretely, due to longitudinal palm crease one can easily bend one¡¯s thumb, and due to two transverse creases one can easily bend the rest of the fingers. At the sole, sole creases are also present, but it is not clear like palm creases. This is because toes are not as free as fingers. ¡°Along with fingers with freedom, humans who are evolving now have clearer palm creases."
I researched about palm creases in order to define Korean's anthropometric characteristics. I looked at lots of university students' palm creases, and thus I was able to compare palm creases of students majoring in liberal arts and students majoring in natural sciences. Lots of people believe that palm creases are related to destiny. Therefore, I was expecting the two group's palm creases to be different, but disappointingly, I did not see a difference. "I cannot declare that palm creases have nothing to do with destiny, but I can assume that they do not. I hold women's hands saying that I will examine their palm creases. Men's palm creases are big and clear, so I do not have to hold hands to see them."
Monkeys use both hands and feet to climb trees, so their toes have same length as fingers. When you visit a zoo, look at the monkey's toes closely. Then, would monkeys be more evolved species than human beings? The answer is no. What is important is the thumb. Among five fingers, thumb performs 40% of the functions. That is, if thumb disappears, 40% of the hand disappears with it. Monkeys have shorter thumbs, and it does not rotate well, so they cannot hold things well like human beings. "The reason why monkeys cannot write is because they cannot hold pens like human."
There is also another difference between human and monkey's hands. In human's palm, there are thenar eminence and hypothenar eminence which connects the thumb and little finger. A monkey does not have sufficient muscle to move the thumb and little finger, so their thenar eminence and hypothenar eminence are not thick as those of humans. As a result, monkeys, unlike humans, cannot touch little fingers with their thumb. "Human cannot climb trees like monkeys, but is the only animal that can type due to the freedom of the fingers"
When studying for an exam, why do people memorize by writing on papers? This is because as hands move, cerebrum also works. Hands are much smaller than legs including feet. However, at cerebrum, parts that hands cover is as big as parts that the legs cover. A human being's cerebrum got bigger as hands developed. In other words, human beings got smarter as they utilized hands after learning to walk with two feet. Like this, hands are closely related to cerebrum. Children playing with toys and dolls are likely to be smarter. "These days people of all ages old hold cell phones and computers. We need to hold other things: pens, instruments, or other people's hands. Then, we can become smarter."