The answer is too obvious for mention. If not environment, perhaps the answer lies in human perception. Maybe our perception is erroneous. I think in this regard of Pelagius, a theologian of the fifth century. He argued that indeed the whole matter is one of perception.
Sin is only imaginary.
The human nature therefore is basically good. The answer here is likewise obvious. It is his thesis that all men have inherited moral corruption from Adam. Yes, it is in the genes and chromosomes. Sin is by imputation.