Racial differences in the prevalence of child abuse probably contribute to racial disparities in both IQ and crime. According to the Department of Health and Human Services, the rate at which children suffer from abuse is roughly 14.6 per 1,000 for Blacks, 8.5 per 1,000 for Hispanics, and 8.1 per 1,000 for Whites. Thus, the Black child abuse rate is about 80% larger than that of Whites and Hispanics.

Some people deny that Blacks abuse their children more often than whites do and argue, instead, that Black child abuse is more likely to be reported. The fact that Blacks are vastly overrepresented in cases of “substantiated” child abuse, such as children being murdered by their parents refutes this hypothesis. Moreover, African Americans are not known for being especially likely to call the police.The weight of all the available evidence clearly suggests that Blacks commit child abuse more often than Whites do.

The Effects of Child Abuse

Being the victim of child abuse is a risk factor for criminality and low IQ. This effect remains after controlling for socio-economic status. Moreover, when one twin is abused while another is not, research shows that the abused twin is, on average, more criminal and less intelligent than their non-abused cotwin. This finding suggests that genetic confounding cannot account for this relationship. Further still, abused children grow up to be more criminal than average even after controlling for birth order, maternal education, paternal criminality, religion, and family structure.

A potential confounding explanation for these empirical results is that children being dumb and aggressive causes their parents to be more abusive towards them. To my knowledge, this has not been adequately addressed in the literature. On an intuitive level, it seems like this has to be true to some degree. However, there is no reason to suppose that this explains the entirety of the relationship between abuse and IQ/crime. For the rest of this article, I will assume that there is some real causal relationship there, though it is probably smaller than what most studies estimate.

Because of its rarity, child abuse explains less than 10% of the variation in both intelligence and criminality in the general population. However, the degree to which being abused increases the likelihood of a person becoming a criminal is hard to estimate. Studies vary in their definition of abuse, the set of statistical controls they employ, and their measurement of criminality. Because of this, estimates of how much being abused increases a person’s chances of being a criminal range from 28% to 200%. No meta-analysis of this data has been done and so there is no simple way to judge the true effect.

The exact mechanism by which child abuse impacts IQ and criminality is not known, but there are many possible causal explanations. For instance, some have suggested that child abuse causes chronic emotional distress in children which in turn negatively impacts their neurological development of traits like aggression, self-control, and intelligence. Another common hypothesis is that abused children pick up the violent tendencies of their parents and are thus made more likely to be criminals.

Regardless of the causal mechanism, child abuse likely causes both low IQ and criminality and is probably an environmental variable which explains some of the black/white gaps in both of these variables.

Impact on Racial Crime Gaps

Black women are roughly twice as likely as White women to be incarcerated. Black men are around six times more likely than White men to be in jail.

It would be nice if, given all this information, we could estimate what proportion of the Black/White crime gap can be attributed to child abuse. Doing so is problematic since there is no consistent finding regarding the effect size of child abuse on crime. Moreover, the impact of child abuse on crime seems to vary by race. Consider, for instance, this data from the Department of Justice:

Here we see that child abuse increased the probability of a White adult being arrested by 27% vs 37% for Blacks. Child abuse had no statistically significant impact on violent crime in Whites at all.

Because of these complications, I don’t feel comfortable giving any exact estimate of how much of racial disparities in crime can be attributed to child abuse. However, it is obvious that Blacks being 80% more likely than Whites to experience a very rare environmental stimulus which increases criminality by 30-200% cannot explain more than a small fraction of why it is that Black men are six times more likely than White men to go to jail.

Impact on Racial IQ Gaps

Research suggests that child abuse typically lowers IQ by 3-4 points. However, this effect is probably stronger for Blacks than it is for Whites. Research has shown that the smarter someone is the less their chances of being a criminal will increase if they are abused. In other words, high IQ people are less vulnerable than low IQ people to the effects of child abuse.

To my knowledge, there are no well-replicated point estimates for the impact of child abuse on IQ by race. Given this, it is once again difficult to assess how much of the racial IQ gap is due to child abuse.

However, Blacks being 80% more likely to experience a very rare environmental stimulus which decreases IQ by something like 3-4 points clearly cannot explain the vast majority of the 15-16 point difference in IQ scores between Blacks and Whites.

A Heritable Environment

Many people conceptualize child abuse as an environmental stimulus. There is an important sense in which this is false: what genes an individual has, as well as the genes that the people around them have, can influence how likely they are to experience child abuse.

For instance, if a kid’s parents are genetically inclined to be impulsive and aggressive they are going to be more likely to abuse their child. Similarly, the evidence we saw before indicates that someone who has a low “genotypic” IQ will probably be more vulnerable than someone with a high “genotypic” IQ to the effects of child abuse.

This can lead to a vicious gene-environment cycle whereby populations which are genetically disadvantaged with respect to aggression, self-control, and IQ, will also be more likely to experience environmental stimuli which will degrade these traits even further.

There are several reasons to think this is happening to Black people.

First, lots of positive evidence shows that Blacks are genetically predisposed to be more aggressive, more impulsive, and less intelligent than White people are. To deny the heritability of racial differences in child abuse rates, you have to either refute this evidence or deny that intelligence, self-control, and aggression, play a role in child abuse.

Secondly, several twin studies have shown that the propensity to commit child abuse is significantly heritable.

Thirdly, while data on child abuse in the 3rd world is lacking in quality, what evidence does exist suggests that male child abuse is far more widespread in Africa than it is in Europe or North America, as would be predicted by a hereditarian hypothesis.

Further evidence that Blacks are particularly vulnerable to the effects of child abuse comes from the MAO-A gene. Certain versions of this gene make abused people more likely to grow up to be a criminal relative to abused individuals who do not carry these gene variants. Blacks are more likely to have these versions of the MAO-A gene.

Of course, low IQ also makes people more vulnerable to the impact of child abuse and, as has already been noted, Black people are more likely to have low IQs.

In conclusion, child abuse is probably an environmental factor in Black/White differences in crime and intelligence. However, child abuse cannot explain the vast majority of either racial disparity. Moreover, this “environmental factor” is itself partly heritable because genetics plays a significant role in explaining both why it is that Blacks are more likely than Whites to experience child abuse and why they have a more severe reaction to child abuse than White people do.