It’s Official – Fathers ARE Important to their Childrens’ Upbringing

David Cameron’s “Broken Britain”, with its image of moral decay driven by the breakdown in family life and poverty, may be inciting a lot of debate in parliament and the public press, but to read many studies of human evolution, you might be mistaken for thinking that the human male has never actually played a meaningful role in childcare. Most evolutionary studies focus on female life history – age at first reproduction, number of offspring and interbirth interval, for example – to the exclusion of the fathers. Those studies which do consider the role of male care in the evolution of human populations usually suggest that their role is indirect, that is that they provide food or other resources to their wife and kids, but are not involved in child rearing directly.

A recent paper in the American Anthropologist focusing on the potential importance of direct parenting by men (Gettler 2010), is therefore a refreshing novelty. It notes that modern humans are unusual among mammals in having both a long childhood (requiring more input from caregivers) and a relatively short interbirth interval. This suggests that individuals other than a child’s mother are likely involved in their upbringing, thus reducing the pressure on mothers and enabling them to have more children.

In many modern human societies, these additional caregivers are fathers (as well as other relatives), but evolutionary hypotheses largely assume that female behaviour is the most important factor in changing reproductive behaviour. The “grandmother hypothesis”, for instance, proposes that the extended post-reproductive lifespan of women caused life-history change, by ensuring mothers could rely upon their own female relatives. Another such model, the “allomother” hypothesis, suggests that other females – maybe young ones practicing their childcare, or other members of the group – were the key. Care by both parents has also been suggested as an important factor, but only relatively recently (Gettler 2010).

Gettler’s hypothesis, though, is slightly different – he suggests that it was men, not women, who caused the change, by getting involved, perhaps for the first time, in the direct care of children, in particular by helping females to carry offspring during population movements. His research is based on assessment of energy expenditure in Homo erectus and later species in our genus (working on the assumption that earlier species likely reproduced with a longer interbirth interval similar to that of a chimpanzee), and builds on the idea that for large bodied hominins, the key tactic to reduce the energetic cost of each offspring was to “stack” them, reducing interbirth intervals, weaning infants earlier and thus lactating for shorter periods. Overall energetic costs of living were relatively high in Homo erectus, especially compared to earlier species with smaller, less “expensive” brains, but reductions in gut size suggest that both trade-off between organs and increased dietary quality were acting to counterbalance the increased cost. This has led to the traditional model for life-history change, which proposes that this increased quality diet relied upon meat, which was hunted by males and given to females by the hunters. This would lead to monogamous pair-bonding, division of labour, and, thereby, to shorter interbirth intervals as women and children were no longer subject to the same selective pressures as their earlier counterparts. More recent studies of hunter-gatherers, in contrast, suggest that gathering provides more calories in the day-to-day life of groups, and researchers now are uncertain whether pre-modern humans would have been sufficiently efficient hunters for this provisioning model to be correct.

Gettler’s model, though, recognises that in fact carrying infants – especially in hunter-gatherer societies where travel distances per day can be long – may be more energetically expensive than lactating, and is not usually alleviated by division of labour. Instead, he proposes, when groups moved around, it was the men who carried the offspring, reducing female energetic costs dramatically and thus (indirectly) enabling them to bear more children with shorter gaps between births. Those males who thus became directly involved with their childrens’ upbringing would have a fitness advantage over those who did not, producing more offspring and perpetuating the behaviour, particularly where males and females were foraging together and ranging over large areas.

In addition to this new model, moreover, Gettler (2010) also notes that this model emphasises the potential complexity of male-child relationships. The energetic benefit to the mother of male carrying of children only pertains in certain circumstances, for example, where foraging is roughly equally efficient in both sexes and hunting is not male-dominated and frequent. This is, in my view, even more interesting than the suggestion that direct male care was important, as it suggests that life-history models are finally coming into line with other fields of palaeoanthropology, in which the complexity of evolutionary processes have been the subject of increasing certainty in recent years. Behavioural and cultural flexibility, and the occupation of variable environments have been emphasised in models of human physical evolution for a few decades now, but life history research has remained focused on the savannah hypothesis until very recently.

I’m not sure what the implications are for the Tories’ social policies on Broken Britain, though....



References

Gettler, L.T. (2010). Direct male care and hominin evolution: why male-child interaction is more than just a nice social idea. American Anthropologist, 112 (1), 7-21 : 10.1111/j.1548-1433.2009.01193.x