First, from Donohue and Levitt’s The Impact of Legalized Abortion on Crime, which argued that the legalisation of abortion contributed to later declines in crime:
More interesting and important is the possibility that children born after abortion legalization may on average have lower subsequent rates of criminality for either of two reasons. First, women who have abortions are those most at risk to give birth to children who would engage in criminal activity. Teenagers, unmarried women, and the economically disadvantaged are all substantially more likely to seek abortions. Recent studies have found children born to these mothers to be at higher risk for committing crime in adolescence. Gruber, Levine, and Staiger, in the paper most similar to ours, document that the early life circumstances of those children on the margin of abortion are difficult along many dimensions: infant mortality, growing up in a single-parent family, and experiencing poverty. Second, women may use abortion to optimize the timing of child-bearing. A given woman’s ability to provide a nurturing environment to a child can fluctuate over time depending on the woman’s age, education, and income, as well as the presence of a father in the child’s life, whether the pregnancy is wanted, and any drug or alcohol abuse both in utero and after the birth. Consequently, legalized abortion provides a woman the opportunity to delay childbearing if the current conditions are suboptimal. Even if lifetime fertility remains constant for all women, children are born into better environments, and future criminality is likely to be reduced.
Second, from Bryan Caplan’s Selfish Reasons to Have More Kids:
Parents have little or no effect on criminal behavior. ...
In 1984, Science published a study of almost 15,000 Danish adoptees age fifteen or older, their adoptive parents, and their birth parents. … As long as the adoptee’s biological parents were law abiding, their adoptive parents made little difference: 13.5 percent of adoptees with law-abiding biological and adoptive parents got convicted of something, versus 14.7 percent with law-abiding biological parents and criminal adoptive parents. If the adoptee’s biological parents were criminal, however, upbringing mattered: 20 percent of adoptees with law-breaking biological and law-abiding adoptive parents got convicted, versus 24.5 percent with law-breaking biological and adoptive parents. Criminal environments do bring out criminal tendencies. Still, as long as the biological parents were law abiding, family environment made little difference.
In 2002, a study of antisocial behavior in almost 7,000 Virginian twins born since 1918 found a small nurture effect for adult males and no nurture effect for adult females. The same year, a major review of fifty-one twin and adoption studies reported small nurture effects for antisocial attitudes and behavior. For outright criminality, however, heredity was the sole cause of family resemblance.
The lesson: Even if your standards are low, instilling character is hard. Genes are the main reason criminal behavior runs in families.
How much of the abortion-crime link (to the extent it is real) is driven by elimination of those more genetically predisposed to crime?