When I was a (what I thought) wise college student there was a debate about how children's personalities developed. There were those who thought children were largely shaped by their environment or learned behaviors - Such as their parents likes/dislikes, discipline, participation of fathers/mothers in the home, culture, etc. The other train of thought was largely based on biology. The child was born with a predetermined personality or set of behaviors that their biological makeup determined. My friends and roommates would occasionally debate this issue. At the time we found ourselves leaning towards the environment side of the argument. Perhaps because we were taking the time to evaluate our own upbringings and its effects on us out in the 'real' world.
WRONG.
All that debate in the academic world and all they really had to do was ask a mother.
Children are not mini-me's. They come with their own personality the day they are born. I use my own children as examples. Madilyn has been, from the day she was born, a high intensity kid. She cried harder, longer, and louder than other babies. She isn't a problem child but she is extremely sensitive to sound, light, taste, texture, etc. I hate the people who put seams in socks. All of these things, when they get out of the parameters Madilyn deems normal, make her completely decompose into the crying tantrums we experienced when she was a baby.
My other two children do not have this problem.
Don't tell me environment has anything to do with the fact that my girls want to wear dresses everyday and that one HAS to have a puffy skirt and other CANNOT have a skirt that is too puffy or she breaks down into tears. (Ok maybe this has more to do with their ages 5 and 3 but come on every day!)
Now, having said all this I know the environment children are raised in makes a huge difference. There are certain behaviors that can be learned. I also now believe there are certain aspects of a child that cannot be changed. As parents we cannot make our children into miniature versions of ourselves, nor would I want to. As parents we get to try to figure out these little creatures with their own personalities and quarks and how we can best help mold them into little people that can function normally in society.
As with most things, the answer is somewhere in the middle between biology and environment. I just want to state that I believe anyone who thinks its entirely environment is wrong. A lot wrong. I'm talking a lot.