Obviously, environment -- if so influential in this situation -- must be overwhelming in the case of human traits. Bah!
Chelsey (17 yo) argued with her mother for 7 months; Chelsey wanted to be a masseuse on a cruise ship after high school graduation. I mentioned in one session that she would have to enjoy rubbing feet like the girl I saw in the shoe store over the weekend. Chelsey dropped her plan. She hated to touch feet; she had no objections to the other parts of old bodies that she might be expected to rub. She also hated anyone's touching her feet. At age 5, she kicked shoe salesmen who tried to touch her feet. She avoids touching her own feet. Mom has the same aversion and to the same intensity.
Arlene -- 4 years old and snuggled to mom's chest, one hand over mom's left shoulder during one of our sessions. Mom talked quietly about her husband, then barked, "No!" and pulled Arlene's hand away from where it had strayed, forming little curls of Mom's hair. "I can't stand when she does that. I'm sure she's doing it just to annoy me." The little girl went back to sleep; her mother continued her list. A few minutes later, the little girl moaned, "No" and pushed mom's hand from where it had been rolling Arlene's hair into little coils.
Ginger (19) has vigilance difficulties and borderline grades. Her younger brother has similar difficulties and momentary absence episodes, perhaps attributable to mild bilateral frontal damage corresponding to the contact points for forceps during delivery. Ginger's mother and maternal aunt both had similar school problems. They were all forceps births.
I would rather believe genetics is the more influential factor than think forceps applied to 4 newborns in 4 hospitals separated by a score of years, produced equivalent outcomes ... especially more severe ones in the male who happens not to have a 2nd X chromosome to balance damage possibly occurring on the 1st X chromosome.
When it comes to specifics, even with humans, I attribute more and more to the genetic contribution.