...that we do with our hands.
Last night I noticed how I was playing with my keys as I was discussing sociology with another person. My thoughts were directed at the subject matter and I payed no attention to other things. My mind was among Marx and arguments about any usefulness of literature in sociological research. And a few times I realized that I was playing with the keys in my hands. I was just doing some random repetitive things to them while talking or listening.
And I could not help to wonder why. Why was it that when I was thinking about something, I had to do something with my hands? In fact, why is it that many other people subconsciously begin twisting a pen or turning their bracelet/watch or playing with hair whenever they are contemplating? Or reading/writing? Or speaking in front of public? What causes this seemingly illogical behavior?
My best guess is: evolution.
First, I am not a psychologist, but I can tell conscious from subconscious activity and these minor movements with a bunch of keys were definitely subconscious. I did not realize I was doing it for most of the time. Furthermore, such things have occurred whenever I (or other people I have seen, for instance my 9th grade English teacher who used to play with her bracelet) were busy thinking about something. Whether it be reading, writing, arguing, watching a video of something, or simply dreaming.
Second, it was manual physical action. In all cases, we either chew the pen/cil or our nails or hair or we twist and turn some small objects that are around or even shuffle a deck of cards (don't ask). Inductive reasoning leads me to conclude that human beings have this tendency of engaging in actions with their hands or possibly teeth.
So, there is a connection between thought and manual activity. When we give in to thoughts, some natural tendency kicks in and compels our hands to do something, whatever it is. What, in turn, could cause that? This is where evolution comes into our considerations.
We, humans, have evolved as users of tools. Basic tools have been a part of the hominids' existence ever since Homo habilis walked the earth 2.5 to 1.6 million years ago. Ever since then, our family, the hominids, have been coerced by the merciless process natural selection to employ tools in order to enhance the population's capabilities of survival. Tools then became spears and bows and hatchets and nets, but the important thing is that there was pressure from natural selection to make those half-apes of prehistoric times use tools.
Now, using tools is a manual activity. The Homo habilis grabs a rock and cleans up some of the meat it found. Later hominids, more reminiscent of us, begin forming the tools to make spears or nets. But it is also an activity that requires thinking. The primitive man has to figure the length and the shape of the spear tip, or the knots of the fishing net. He has to use his imagination and reasoning capabilities to make or use the tool against prey. Thus, there has been a certain connection between thinking and manual activity connected with tools. This connection has existed for millions of years in our evolutionary history.
The exact reason, according to this explanation, then, is that natural selection has forced humans to be more attentive on the tools they were making or using. It stands to reason how - whoever failed to make a good hatchet or to thrust the spear well was less successful with hunting and getting food and staying alive. In case of fighting predators, less successful in maintaining personal safety and fighting back. Thus, the process of natural selection has applied pressure against our species as it evolved and has led to the thinking process to be somehow bound to using one's hands. It has been going on for 2.5 to 1.6 million years now. And still lingers.
Alternatively, the subconscious manual activity that I have observed could serve a different purpose. First of all, it is subconscious. This means that the hands are doing one thing, while the brain is processing information about another. In my case the hands are tweaking the keys, while the brain is tweaking sociology. What does this lack of relation imply? It implies that natural selection could have, au contraire, given us the ability to split our activity into two. While the hands automatically do something monotonous and not requiring our attention, our brains are free to tackle other issues that we face and imagine possible solutions. Back in the days this would have looked like the man sharpening his spear, thinking about where to hunt next.
I realize that this is a rough and incomplete explanation. It does not account for chewing pencils or gum. It may also be arguable from evolutionary psychological point of view. But it is worth mentioning.