Our foraging ancestors weren’t particularly war-like

Few subjects more predictably animate furious disagreement and cross-purposes discussion than the origins of human warfare. Are people “naturally” belligerent? And what does that even mean?

The question taps a deep old well of ideological intuition. Were the lives of our ancestors, as Thomas Hobbes’ infamously put it in the 17th century, “nasty, brutish and short”? Or, were our ancestors more like the “noble savages” of romantic primitivism? Our beliefs about these issues colour whether we feel our lives are generally better or worse than those of our ancestors.

This dichotomy, in more nuanced forms, has haunted and at times paralysed anthropology since at least the 19th Century. And it reared its head again recently with the divisive reception granted to books such as Steven Pinker’s The Better Angels of our Nature, and Jared Diamond’s The World Until Yesterday, as well as a flurry of renewed interest in controversial anthropologist Napoleon Chagnon.

Steven Pinker outlines his case that violence has steadily declined throughout history

From my reading, the evidence stacks pretty solidly in favour of Pinker’s thesis that violence has decreased dramatically throughout human history. As John Armstrong put it in his review of Pinker’s book, The World Has Never Been as Safe and Peaceful as it is Now. But Pinker continues to attract considerable static, particularly from those quarters where pessimism about modern life and paranoia about Western imperialism run hottest.

But the overall battle over the decline of violence is but one theme in the history of violence, a history replete with intriguing sub-plots. The prevalence of warfare among mobile forager band societies occupies a place of particular controversy among anthropologists who actually work in the field.

Until 10,000 years ago, the ancestors of everybody alive today lived in small nomadic bands and foraged what food they could catch or gather. Most of our species’ recent past – hundreds of thousands of years – was spent hunting, gathering and moving about in this way. As a result, accounts of human adaptation often consider in some depth this period, given its importance in determining which genes and traits our ancestors bequeathed to us.

A small number of “mobile forager band” (MFB) societies still exist – or persisted long enough for anthropologists to study them systematically. It is from these peoples that we draw almost everything we know about the way our ancestors lived until the seismic changes wrought by agriculture.

From modern accounts of MFB societies we can infer that our ancestors were certainly violent. Ethnographies document homicidal personal disputes, spousal killings, fights among men over women, executions of outsiders and inter-group killings.

But were our MFB ancestors war-faring? War, here, is a subset of lethal violence that involves members of a group working together to overcome members of other groups. It’s one of those appalling human traits that romantics would like to pretend doesn’t happen elsewhere in the animal world. But ants, by this definition, certainly wage war among colonies. And Jane Goodall’s discovery in the early 1970s that chimpanzees from one group occasionally work together to kill members of other groups suggests our closest living relatives look pretty war-like too.

Harvard Anthropologists Richard Wrangham and Luke Glowacki argued in a recent paper that our ancestors waged chimp-like warfare, launching coordinated surprise attacks on other groups. Raids of this sort, in order to weaken other groups, or capture livestock, property or women, are a feature of every society that has domesticated livestock, horses or agricultural crops. But these societies tend to involve bigger, more complex groups, and forms of wealth more worth fighting over than MFB societies.

Mobile forager bands have more characteristically egalitarian political structures, less coalition-forming behaviour, and few resources or possessions worth defending. These properties don’t make good ingredients for war-mongering. So it’s really worth knowing just how much of MFB violence can be considered warfare. As my post-doc advisor was occasionally heard to say:

Just get the data!

Last week’s edition of Science contained an exhaustive analysis by Douglas P. Fry and Patrik Söderberg, who scrutinised the existing accounts of all lethal violence in 21 MFB societies. They tabulated the causes of 148 cases of lethal aggression, and found that two thirds originated from within-group conflicts. The majority of these deaths were caused by a lone perpetrator.

Only one third of events could possibly be construed as acts of warfare. And most of these events occurred in one society – the Tiwi of northern Australia in which ethnographers documented several intergroup disputes and revenge-seeking cycles. In the other 20 MFB societies only around 15% of deaths by lethal aggression could possibly fit the definition of war.

The authors concluded that:

most incidents of lethal aggression among MFBS may be classified as homicides, a few others as feuds, and a minority as war.

Refreshing as it is to see a calm, data-driven approach to answering a tightly-proscribed research question, the prevailing discussion over the last week has fallen into old ruts.

“War arose recently” proclaimed ScienceNews. Fair enough. I don’t think Fry and Söderberg would contest the argument that agriculture and the rise of complex societies made war a worthwhile – in the economic sense rational – option. And that stoked the body count.

But the Socialist Worker led, as it does, the charge against scientific accounts of human nature. War Not Due to Human Nature it proclaimed, reeling off a link-fest of SW diatribes against scientific accounts of human behaviour, and then linking to a somewhat more considered piece from Slate.

I’m happy to grant that these data show that MFB societies don’t make as much war as agriculturalists and pastoralists, not to mention contemporary weapon-rich societies. But I’m intrigued about the Tiwi, who don’t fit the mould. I’m not familiar with the data, but according to ScienceNews, Samuel Bowles reckons the Tiwi were among the more peaceful hunter-gatherer societies he studied in an earlier Science paper that reached more bleak conclusions about the history of war.

And I’m equally intrigued by how societies can tip so quickly into belligerence as soon as they settle down and accumulate some wealth. The capacity to form coalitions and deploy them for ill may have been there all along.

Where did that come from?

Rob Brooks does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.

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When men were boys – demographic data shows male puberty starts 4 years sooner than it did in 1800

You’ve no doubt heard that girls are entering puberty earlier than they ever have before. It’s one of those science-lite stories beloved of tabloid papers and current affairs programs. One recent article had 10 to 15 percent of American 7 year olds showing the first signs of breast development.

It’s one of those problems that has folks scratching around for an answer. Toxic chemicals in the environment, including those that fake the effect of hormones, often get the blame. Diet – specifically the overnutrition that’s also causing childhood obesity to balloon – is another popular culprit.

There are plenty of reasons to be concerned. Hormonal disruption can cause all sorts of diseases, including breast cancer. Likewise, obesity can lead to type II diabetes, coronary heart disease and many cancers.

Figure 1 from Goldstein's paper, shoing the 'accident hump' in male mortality.

Beyond these problems that might beset girls later in life, maturing too fast can make life difficult for little girls. Young girls can be notoriously precocious, and it isn’t hard to imagine that an 12-year old who looks 17 could find her world a bewildering and even dangerous place.

The start of breast development is thought to signal the beginning of puberty, and can be measured easily. Even better, the age at which a girl reports her first menstruation gives and unambiguous and easy to remember measure. And records go back a very long time, confirming that girls are experiencing menarche, on average, at younger ages.

But what about boys? It isn’t quite as easy to measure the onset of puberty in boys as it is in girls. An innovative new paper by Joshua R. Goldsteinat the Max Planck Institute for Demographic Research in Rostock, Germany, makes use of a rather unfortunate quirk of male demography to do so.

Both girls and boys experience declining mortality rates throughout childhood and early adolescence. For a brief period in the early teens, as girls enter menarche, their mortality rate slowly begins to rise, and it continues to do so gradually until around 50, at which time it takes off (see Figure 1).

About half a year after girls’ mortality begins to rise, boys also begin to die at much faster rates, and their chances of dying outstrip those of women until they reach about 30 years old.

This “mortality bump” is a famous feature of human demography. It occurs because pubescent and young adult boys suddenly become much more likely to die in accidents and violence. In a very short time, many boys go from relatively cautious children to wild thrill-seekers. Evolutionary psychologists reckon the burning desire to take risks comes from a furious jostling for respect and acceptance among male peers, and an urge to show off to girls.

Likewise, Martin Daly and Margo Wilson’s exceptional work on the causes of homicide shows that the most common form of killing, in which young men kill other, unrelated young men, tends to be the tip of an iceberg of simmering masculine rage. The urge to retain this respect and to compete with rivals can turn an otherwise innocent look or bump into a violent confrontation, some of which end in homicide.

Goldstein recognized that demographic records hold valuable information about the timing of male adolescence. Instead of finding out when each boy reached a particular landmark in development and then calculating the average age, he realized that the timing of the ‘accident hump’ could reveal the average age at which whole cohorts begin to behave like adolescents,

Figure 2 from Goldstein's paper, showing the decrease in age at which the accident hump manifests.

Sweden has kept fastidious demographic records for over 200 years, and several other countries have done so for almost as long. It turns out that over two centuries, young men have begun to mature a full four years earlier (see Figure 2).

Just as early pubescence in girls raises unique worries, so too we should  worry about ever younger men entering the period of anger, recklessness and relentless striving to impress peers and possible partners.

It is a problem that has long concerned Sir Peter Gluckman, the Chief Science Advisor to the New Zealand. He wrote a fabulous book, Mismatch: Why Our World No Longer Fits our Bodies, in which he discusses this and other ways in which our evolved bodies are no longer adapted to modern conditions.

Gluckman told the New Zealand news site stuff.co.nz that “MRI scanners have looked at the brain over time to see how it matures and several studies have shown quite dramatically that the last parts to mature deal with things like logic, judgement and wisdom. Those scans show they may not be mature until people are 25 to 30.”

While modern safety standards in developed nations probably make industrial and agricultural accidents as well as accidental drowning and homicide less likely than they were in 1811, we have invented plenty of new ways for young men to kill themselves since then. Foremost are personal firearms and that deadliest of weapons, the motor car.