What makes a person who they are?

Answer 1

We know from research on twins that at most, only 50% of the variance of a given trait (e.g. intelligence) can be attributed to genetics, with the rest attributable to individual environment. Humans, from conception, come with such complex genetic baggage, including the ability for language, social organization and rational thought, that we have only begun to study how our genes interact with our environments to produce the six billion plus individuals now inhabiting our planet. If we consider from the other end all the possible environments in which to live and all the variations within even the seemingly most mundane existence, we can begin to understand the magnitude of trying to parse all that goes into making an individual.

From individual genetics we go to the immediate family and the family environment, determined by parents, siblings and others living in the household. From there we consider the local community, including friends, schoolmates, teachers, etc. The local community exists within a larger culture, and most likely that local culture is itself part of a greater nation. With the ease of communication in today's computer age, national boundaries are no boundaries to the transfer of ideas, so ultimately the entire world goes into the making of an individual.

Answer 2

DNA. People have different genetic codes and when they have kid, the two DNA from the parents mix together and form a unique set of DNA for the offspring. Also, DNA naturally mutates over time.