What makes you say that being willing to abort your baby is genetic? Wouldn’t it be just as likely environmental?
The reason I don't think environmental factors have a large impact on abortion is that despite a strong, over-the-top campaign to promote abortion ongoing since before Roe v. Wade, the abortion industry has been losing ground for years. If the incidence of abortion were strictly due to environmental factors, every woman of childbearing age would be using it as birth control, because it has been promoted that strongly. In reality, few do. (In comparison: recycling has also been promoted for decades, and few people even question the practice.)
The decision to have an abortion takes place long before an "unwanted" pregnancy occurs. Once that decision is made, the behavior that leads to an abortion follows. From that fact, we can extrapolate that only women with certain personality traits would make the decision to engage in that kind of behavior. Furthermore, the maternal instinct is extremely strong; only a woman whose willpower is strong enough to overcome that instinct is able to have an abortion. Those who have abortions do not have as many live children as other women, both because of personality, and because physical damage resulting from abortion decreases the likelihood of carrying a child to term. Because personality traits and the ability to suppress the maternal instinct are controlled genetically, the genes involved are being weeded out of the population.