Originally posted by Kerrie
a very basic question that i wonder a lot about...here we are on this earth, along with all the other forms of life, we physically must survive in the same manner - requiring sleep, food, adequate health - yet, personality wise, we are unique...why? this question is not limited to human beings either, as my roommate's dog has quite the personality for example...
Well I'm no neuroscientist, but according to what I think I understand...
Genetics determine a lot of things about our brains, but that is all modified by other conditions as we grow into an infant. Then, as we experience more and more, those experiences build on one another, creating unique conditioned responses, opinions, attitudes, and so on. In short, we are unique because we lead unique lives.
It is all based on how brains work. You can imagine the primate brain (and other somewhat intricate brains) as having two major areas (It's a lot more complex, but this simplistic way of dividing it is good for my point for now). There's the higher brain and the lower brain.
The lower brain (sometimes referred to as the instinctive or "lizard" brain) consists of the brain stem, cerebellum, and a few other parts. It's lower in the physical sense but also in an evolutionary and complexity sense. You'll find this area in everything all the way down to ants. It's the dominant "behavior maker" in animals (and some people who are brain damaged or who have suffered extremely traumatic early lives). In this area, the nerves are "hard wired", the cells have specific connections that are directly determined by DNA and don't change very much. This wiring is also a lot simpler. The simplicity of these connections mean that responses are quick and efficient, but it also means that they are crude and simplistic. This area gives us most of our instinctive impulses. Someone throws something at you and you react without "thinking about it" for example.
The upper brain is made up of "unspecialized brain cells". In these the DNA says, "here's the brain cells and how they act individually". Then, the experiences you have via your sensory input (sight, smell, taste, touch, feel) cause connections to form between the neurons (a type of brain cell). The nature of these experiences determines how and where the connections form and how strong they are. This not only codes all your memories, but also forms your "personality", or at least a good deal of it (remember the lower brain is still there and competing for attention). So, since everyone's experiences are different, these connections are different, and therefore give you a different personality than others. The good thing about unspecialized brain cells is that they can customize to the needs of the individual so s/he doesn't have to wait millenia for evolution to adapt his/her whole species. The bad thing is that the upper brain, being much more complex, tends to be slower and the connections more tenuous. That's why instincts feel so much more powerful an impulse than decisions made intellectually, and why it takes longer to come to complex conclusions than to react to being pricked.
So your upper and lower brain are constantly competing for "control" of you. This is the old thing about controlling your impulses and doing something even if you know it's not a good idea (like eating cheesburgers or cheating on a spouse - not to equate the two!).
An interesting thing I saw once was a study where they weighed the brains of children that had died. Some of them were from stable loving homes, and others were from abusive or otherwise threatening environments. What they found was that, for those children that developed in threatening environments, their lower brains weighed more in proportion to their upper brains, and vice versa.
This, as it was theorized, was due to the fact that when areas of the brain are used more they form more connections (these connections are physical and so have weight). The brain adapts to environmental needs so this happens. The result is that the lower brain will be more likely to overpower the upper brain whenever a conflict occurs (like you're mad and want to hit someone, but your upper brain knows you'll go to jail and shouldn't). This may give a little insight into why an unhealthy upbringing may lend itself more often to criminal behavior (although not a certainty, as many exceptions surely exist).
Dogs have some "upper brain" too, but not as much as us. Nevertheless, it's enough to learn tricks and develop their own personalities. In general, the more upper brain a species has, the more individualized it's members will be. For example, ants have almost no upper brain. Most all of their behavior is genetically determined so you won't see a great deal of difference between individuals, even if you give them vastly different experiences.
So, our personalities have a lot in common. We all like to be loved, we have a propensity for anger, jealousy, and so on. We all laugh, etc. A lot of this comes from the fact that we have the same DNA as a species, which gives us the lower half of our behavior. The areas where we differ are mostly due to that ability of the upper brain to form according to individual experience.
(note: the brain is actually a lot more diverse and complex than this would indicate, but this abstraction helps to get across a general way the whole personality differences thing works, at least as I understand it.)
