I think people with chimerism might have a different opinion. They're individuals who contain two sets of DNA.
More intriguing, to me at least, are the experiences of conjoined twins in this regard. Their beliefs and activities call into question the view that DNA and even profoundly shared experiences are enough to lock individual behaviour into a specific pattern determined even by the powerful combination of genetics and environment.
People have mapped the genome, but that doesn't mean we've achieved anything like a deep understanding of how most of it works.
Conjoined twins share not only their DNA but every single life experience except their dreams, and yet a review of the very closest among them whose cases are discussed in public shows they retain separate personalities.
...in one case, very separate. (Explain that one.)
Individuation is so strong it even exists among the very rarest of the rare - a set of conjoined twins who may be the first survivors of their kind in the whole of human history: They share a strip of brain matter and can, or so scientific tests indicate, see through each other's eyes. Nonetheless, despite sharing brain matter and sensory information, they're two people rather than one.
The reason I'm focusing on conjoined twins specifically is because, of all the people on Earth, the genetics, epigenetics, and even anti-body profiles of conjoined twins should be, as far as I know, identical. Nurture should be alike as well. They themselves should be highly alike.
Stamped on all their genes, in every cell, is the reality that conjoined twins - especially the Hogans, who share sensory information - should be the most alike persons on Earth. They have more in common than any other two people, including even identical twins, in that conjoined twins must always work together. And yet their sense of difference - and sometimes it's so profound a sense they'll risk death as adults to split - is enough that anyone who pays attention to what these people say will know they're separate individuals.
(There is a lot of information on the people I mention: Documentaries, as well as both news and some scholarly articles, are available online like fruit ripe for picking. And so, too, is information on transgendered people.)
And before jackasses start wondering if they try to widen their own sense of division to prove their individuality...why would they? They're so profoundly connected they cannot be separated. If genetics were the sole determiner of personality, they'd act alike. They should have no problem with the arrangement, and care only a little (if at all) whether or not they're seen by others as one person or two.
But they most definitely care. Why?
A lot of people who decry transsexuality also believe in the concept of a soul among the religious, this is a part of the individual that exists outside the world of materialism - and yet these are the same people who flatly ignore the subjective experiences of millions transsexuals, homosexuals, and so on; they ignore a lot of people - to adopt a view that is more materialist, in some ways, than that of the average atheist. They're arguing, 'What you see is what you get' and this is despite not only the issues raised above but also it ignores the inconvenient-for-them existence of people with XXY chromosomes (however that reality physically presents itself in a child born thus).
People like Wuli (based not only on this OP but the other one as well) abuse science for the sake of exclusion but totally ignore findings that contradict their worldviews. Their concern for "truth" begins and ends with the material they gather - if any - in an effort to prove what they already believe.
