Nature

Picture, if you will, a set of identical twins.

These two twins were separated at birth, and adopted by families of a similar financial status on either side of the continental United States. Thirty-six years after they'd been separated, the two brothers found one another.

Both were named Jim. They both worked in law enforcement. One named his son James Alan, while the other named his son James Allan. They each had been married twice, and were in the habit of leaving notes to their wives on the kitchen table each morning before they went to work. Their dogs had the same names, they lived in similarly-styled houses, slept on the same side of the bed.

Sure, similarities are seen when we go looking for them, but to that degree? It simply couldn't be possible without some sort of genetic connections.

You are who you are because of nature.

In addition to twin studies, adoption studies help to answer the nature-nurture question. If nurture was the real answer, would adopted children consistently share personality traits with their biological parents, as opposed to their adopted ones? Certainly not.

Studies show that genetic predisposition and prenatal environment--that is, the chemicals that are present while genes are developing--have a 40-50% odds of changing a child.

Parental influence has a 10% effect on a child.

Nature is even in the numbers.