By far the largest factor in who you are is your heredity, not your environment. And this drives the Left to paroxysms of denial.
Here are some extracts from an article on twin studies from Quillette, which is an excellent source of information.
In 2000, the psychologist Eric Turkheimer concluded that the evidence from behavioral genetic data was consistent enough to summarize in three laws. The first law holds that all human traits are heritable (i.e., genetic differences account for phenotypic differences) to some degree. This assertion may not seem all that surprising today, although the word ‘all’ is still considered provocative by some. However, twin studies have produced copious data demonstrating that almost every trait is heritable to some degree or another.
The remaining two laws concern environmental influence. The second of these holds that the effect of being raised in the same family is smaller than the effect of genes….
The third law holds that a substantial portion of the variation in complex human behavioral traits is not accounted for by either the effects of the genes or families. In other words, while about 50 percent of the variation is due to the environment, this environmental effect does not come from the family. Instead, it may be produced by the wider culture, society, the neighborhood, school, peer-groups and friends, but also simply chance: random encounters or openings in the social hierarchy, cosmic rays that damage a piece of DNA, neurons that go zig instead of zag, and so on.
Twin studies have uncovered the enormous importance of genetics. They have laid to rest the notion that parents are omnipotent sculptors, and a child is a piece of clay. They have hammered another nail into the coffin of the Freudian guilt complex, where everything that goes wrong in an individual’s life may be attributable to poor parenting.