In a new NBER paper, a group of economists, including James Heckman, have joined with researchers who study child development to analyze data from a multi-generational monkey raising experiment. It’s well known from the Harlow experiments of the 1950s that monkeys raised without their mothers don’t do so well. (It’s also from these experiments that the mantra of skin-to-skin mother-child contact comes from.) What’s distinctive in the new paper is that there are two generations of monkeys who are raised by their mothers or in nurseries and in each generation the treatment is randomly chosen. Indeed, I believe this new paper includes the children of monkeys discussed in this earlier paper which also included Heckman. The multi-generational experiment lets the researchers test whether disadvantage is transmitted down the generations and whether it can be alleviated.
The analysis indicates first that being raised by a mother results in better health and higher social status than being raised in a nursery (as measured by who wins disputes and ELO scores similar to those used in chess!). Second being raised by a mother who was raised by a mother is better than being raised by a mother who was raised in a nursery. The latter indicates that disadvantage transmits down the generations. Indeed, being raised by a mother who was raised in a nursery is just as bad as being raised in a nursery. In other words, it’s hard to ameliorate disadvantage in one generation.
The sample is small (about 100 monkeys in generation one and 60 in generation two) but because of random assignment still potentially useful.
The authors suggest that there are lessons for humans:
Our findings are in line with results from a social experiment on humans. Heckman and Karapakula (2019) document the intergenerational effects of the Perry Preschool Project,which was a randomized social experiment in the 1960s that provided high-quality preschool experiences to socially disadvantaged children. They find that the positive effects of the preschool program were transmitted into the next generation. The offspring of the treated participants were more likely to have better health, achieve higher education, and were more likely to be employed than the offspring of the non-treated participants. In the same way that early-life advantage via maternal presence for rhesus-monkeys led to improved health and higher social rank for their offspring, early-life advantage via high-quality preschool in humans led to better health and social outcomes for their children.
But note the subtle shift in “treatment” meaning. In the monkey experiment, mother-raised is better and it’s the nurseries which are bad but in the human experiment it’s the nurseries that are good. It’s hard enough to justify external validity across human experiments in different places or times doing so across species is an even more perilous leap.