The Perils of Group-Living
– by Robin Dunbar
Solving the problem of how to live in large, demographically stable groups is probably the single most important achievement of anthropoid primates, and especially so of humans. Group-living does not come for free. A variety of centrifugal forces constantly threaten to destabilise groups. One of these is the infamous public goods dilemma. Being willing to live in a group with others involves – necessitates, in fact – an implicit promise not to cheat on the deal. I have to allow you a fair share of the benefits, just as you have to allow me a fair share. However, as we all know, it always pays me to take a bit more than my fair share because, by doing so, I gain a modest but significant fitness advantage on you – at your expense, of course!
If access to benefits is a function of physical strength, then it will always pay those who can get away with it to use a little extra force to extract a few extra benefits. The issue for everyone else is how much exploitation should you be prepared to put up with as the price of living in the group – given that the opportunity cost (or, as economists used to call it with a lot more literary imagination, your regret) is to live alone and miss out on all the genuine benefits of group life?
The Norse world of medieval Iceland was the archetypal example of the problem. With no formal political structures (it was the Wild West of the early medieval period), it lacked judges and police to enforce good behaviour. The result was that violence was endemic and very disruptive. It spawned psychopaths with fiercesome reputations. One such individual was Egil Skallagrimsson, who made himself very rich by shamelessly helping himself to a lot of other people’s land and property (and occasionally wives). If necessary, he simply killed you. Such behaviour often generated vendettas that dragged on for years. In one such case, a third of all the adult males in the community were killed in a vendetta that lasted a generation. Of 23 families, four lost all their males; only 11 survived without losing any. Analysis of data from hunter-gatherer societies indicates that the proportion of all deaths that are due to homicide increases linearly with living group size, such that in bands of just 50 people half of all deaths are due to homicide (Dunbar 2022). Why do small scale societies put up with this?
In one sense, of course, they don’t. As I have shown (Dunbar 2022), what they do is introduce social institutions that allow them to manage violent behaviour, especially among the young males. These include marital arrangements that increase the number of people who can lean on badly behaved individuals, charismatic leaders (whose friendly advice we heed out of respect), communal feasts (where we bond) and, especially, men’s clubs (where boys who fall out are made to sit down together to make peace – without, by the way, actually talking about it, just by bonding).
This is all very well, of course, but it ignores the elephant in the room: bad behaviour pays. This raises the intriguing question as to whether there is a significant selection factor favouring bad behaviour that promotes whatever genes might be involved, despite the costs to the rest of the community?
Many studies have tried to determine whether violence pays by determining whether males who murder gain more wives and/or reproduce more often. Broadly speaking, they do. But, as the ecologist David Lack (of Lack’s Principle) reminded us back in the 1950s, pumping out babies doesn’t necessarily translate into loads of grandchildren. As often as not, having too many babies results in many dying, such that fitness is lower.
At this point, the medieval Icelanders come to our rescue, because they left us an amazing literary record of their daily lives – the family sagas (or histories) that recount in considerable detail the goings-on in the various communities and families, not to mention who married (or otherwise) who and what offspring they had. Using these records, the Viking Age historian Anna Wallette (of Lund University, Sweden) and I have been able to place all the family pedigrees into a single interlinked database of over 1200 males, for a great many of whom we can trace their ancestry, siblings and descendants over 3-5 generations. We used a sample of 13 known killers (who had killed 1-19 other men) and 31 non-killers to test whether killers had higher fitness than socially matched non-murderers – not just in terms of their own descendants but also in terms of the fitness of their collateral male relatives. In other words, for the first time, we were able to test the hypothesis that violence pays by examining inclusive fitness.
The results (Dunbar & Wallette 2024) revealed that, despite having a 40% higher risk of being themselves killed than the average non-killer, killers had twice of many wives and offspring as matched non-murderers (men who were never recorded as murdering anyone) and nearly four times the inclusive fitness through their male siblings – providing they themselves survived to die in their own beds. More importantly, the brothers benefitted enormously: if the killer survived, their inclusive fitness was around three times that of the brothers of a non-killer.
In other words, violence does pay. This does not, however, mean runaway selection in favour of ever more violent individuals. Too many violent individuals would cause the collapse of communal life. Since our capacity to survive and reproduce depends on the group, this would negatively impact our fitness. In the end, it is a balance of the costs and benefits. Humans seem to be especially good at finding social controls that allow us to live in unusually large groups – not because we are naturally altruistic, but because we are good at finding workable solutions. Viking Iceland offers us a glimpse of how bad it can become when the social controls are absent.
Read the original article: Dunbar, R.I.M. & Wallette, A. (2024). Are there fitness benefits to violence? The case of medieval Iceland. Evolution & Human Behavior 45: 106614
