hi doma,
i think it starts with the egg and the sperm. that's to say, we are the construct of what we inherit to some extent. they say that republicans are republican because the wiring in their brain makes them so - perhaps less compassion than is usually available (!).
identical twins are often similar, but never actually identical. eg one may be extrovert, the other more studious but they are both sentimental and look alike. nature. nurture. etc
i am not sure if you can scientifically assign percentages and even if you can, i am not sure if averages are especially useful (dispersions from the mean would likely make averages misleading).
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