Inheritance of abuse in rhesus macaques

Dario Maestripieri (U of Chicago) has a paper in PNAS demonstrating the transmission of abusive parenting style from mothers to their offspring in macaques. The abstract:

Maternal abuse of offspring in macaque monkeys shares some similarities with child maltreatment in humans, including its transmission across generations. This study used a longitudinal design and a cross-fostering experiment to investigate whether abusive parenting in rhesus macaques is transmitted from mothers to daughters and whether transmission occurs through genetic or experiential factors. Nine of 16 females who were abused by their mothers in their first month of life, regardless of whether they were reared by their biological mothers or by foster mothers, exhibited abusive parenting with their firstborn offspring, whereas none of the females reared by nonabusive mothers did. These results suggest that the intergenerational transmission of infant abuse in rhesus monkeys is the result of early experience and not genetic inheritance. The extent to which the effects of early experience on the intergenerational transmission of abusive parenting are mediated by social learning or experience-induced physiological alterations remains to be established.

I think that nongenetic inheritance of behaviors is a very important, and usually underestimated, source of variation in survival and reproductive success. In mammals especially, individuals learn much from their mothers. Foraging strategies are the most obvious learned behaviors, but parenting styles are perhaps equally important. "Good" mothers can be expected to have more healthy offspring, who should be better prepared for interactions in social groups, and ultimately better able to raise their own offspring well.

The hard question is, what is good? Outcomes of individuals pursuing different parenting strategies are difficult to assess. In particular, in this case it might seem intuitive that the abusive parents would reduce the fitness of their offspring. But primates experience a range of stresses in social interactions, so it is not so easy to predict whether a particular kind of maternal abuse will further compound the negatives. Perversely, it might help prepare the juvenile for stresses later in life, or insulate them against stresses from other individuals. We just don't know. It could be that abuse is a short-term dysfunction that naturally would disappear, or it could be that it is an alternative evolutionary strategy that persists at some frequency in natural populations. Telling the difference would require observing natural populations for many generations

This pattern of inheritance is not usually considered to be cultural. Indeed, Maestripieri notes that he doesn't even know whether it is learned. An alternative is that it is a manifestation of innate psychological mechanisms after exposure to a childhood stressor, which may not be unreasonable since the exposure begins so early in infancy (within the first month after birth). But it has implications for the evolution of social learning and culture. Fitness differences that stem from learning ultimately must underlie the evolution of cultural capacities. The mind has patterns that make such learning possible, and these patterns are themselves complex adaptations.

So for the origins of culture from the initially noncultural, relatively complex inherited behaviors like this one may make a template with some predictable features.

References:

Maestripieri D. 2005. Early experience affects the intergenerational transmission of infant abuse in rhesus monkeys. Proc Nat Acad Sci USA 102:9726-9729. Full text online