Cooperative breeders, where we count on the help of others to raise offspring,is not unique to humans. It may only appear that way.

A new paper amassed data from 90 human populations comprising 80,223 individuals from many parts of the world — both historical and contemporary. They compared the records for men and women to lifetime data for 45 different nonhuman, free-ranging mammals. The argue that humans are a non-exceptional species of mammal. Says first author Cody Ross, PhD, anthropologist at the Max Planck Institute; “we can quite successfully model reproductive inequality in humans and nonhumans using the same predictors.”

The scholars say there is greater reproductive egalitarianism in societies that allow for polygynous marriage than in those where monogamous marriage prevails.  Yet among men and women it is distinct.

Yet among mammals, human males stand out in egalitarian parenting

The fact men are relatively egalitarian compared to other animals reflects our patterns of child rearing. Human children are heavily dependent on the care and resources provided by both mothers and fathers — a factor that is unusual, but not completely absent — in other mammals, the authors say. The critical importance of the complementary nature of this care — that that each parent provides different and often non-substitutable resources and care throughout long human childhoods — is why we don’t show the huge reproductive variability seen in some of the great apes.

To support these inferences, however, anthropologists need more empirical data. 

Monogamy 'can drive significant inequalities among women' 

Monogamy can promote large differences in the number of children couples produce, resulting from large differences in wealth in such economies.  In polygynous systems, in which men take several wives at the same time, women tend to have more equal access to resources, such as land, food and shelter — and parenting help. This is because women, or their parents on their behalf, favor polygynous marriages with wealthy men who have more resources to share.

“It turns out that monogamous mating (and marriage) can drive significant inequalities among women,” says Prof. Monique Borgerhoff Mulder at the University of California, Davis.