Zitat:Ferguson (2013) reviews archaeological data on prehistoric warfare for Europe and the Near East. For Europe, the Upper Paleolithic shows negligible evidence of war, and barely any evidence of interpersonal violence. In the Mesolithic, from the onset of the Holocene around 11,600 BP (before present) until the arrival of agriculture, warfare is 'scattered and episodic'. This period is associated with increasing sedentism, more food storage, more distinctive group identities, and greater inequality. About 500–1000 years after the Neolithic transition to agriculture, warfare became widespread, and during the subsequent Copper, Bronze, and Iron Ages, warfare was the norm.

For the Near East, Ferguson's account begins with early Natufian society around 15,000 BP, which was pre-agricultural and similar to the European Mesolithic. There is no skeletal evidence of war in the southern Levant for the next 10,000 years. Likewise, there is no evidence of fortifications in this period. Peace came to an end in the southern Levant in the early Bronze Age around 3200 BC, a time that coincided with the formation of the Egyptian state. The apparent absence of war over this time span is remarkable in light of the intensive archaeological study the region has received

Zitat:Ferguson reviews a substantial body of evidence indicating warfare in other parts of the Near East, including Anatolia and the northern Tigris area, at least as early as the Pottery Neolithic, beginning around 8400 BP. At some sites, warfare probably goes back to the Pre-Pottery Neolithic A, from 11,600–10,500 BP, when agriculture began to arise in southwest Asia.

Zitat:The Standard Cross Cultural Sample, or SCCS, is a representative sample of 186 well-documented and culturally independent pre-modern societies (Murdock and White, 1969, Murdock and White, 2006). Two results from this data set stand out (Kelly, 2013a, Kelly, 2013b). The first is that while there is evidence for warfare in all types of societies, the incidence of warfare is lower for egalitarian nomadic foragers than it is for non-egalitarian sedentary foragers. The second (first reported in Keeley (1996)) is that population pressure is correlated with warfare while population density is not, where population pressure refers to population relative to total food, and population density refers to population relative to total land.

Zitat:Our theory helps explain Ferguson's (2013) finding that in Europe, warfare was rare or non-existent in the Upper Paleolithic, sporadic in the Mesolithic, and common in the Neolithic and later. The small foraging bands of the Upper Paleolithic probably had fluid social boundaries, with easy individual mobility across groups through exogamous marriage and kinship networks. At very low population densities it would also have been difficult to exclude outsiders from a territory, leading to open access conditions (Dow and Reed, 2013). Moreover, the foraging bands of the Upper Paleolithic almost certainly had Malthusian fertility dynamics. Together, these factors would make warfare unlikely.

The shift to the Mesolithic and the Neolithic was associated with rising sedentism (Dow and Reed, 2015) and social segmentation (Kelly, 2000, ch. 4). This would make it harder for individuals to move among groups. In addition, community sizes were rising. Research on recent small-scale societies suggests that this probably made endogamous marriage more common (Dow et al., 2016), reducing kinship linkages across groups and increasing mobility costs for individuals. In combination with the shocks resulting from technological and environmental change, this would have made warfare more common.

Our results are also consistent with stylized facts from anthropology. The model accounts for the empirical finding that warfare is a function not of population density but rather of pressure on food resources.

Zitat:The evidence from Section 2 suggests that warfare is more common among farmers than among mobile hunter-gatherers. This appears to be true even for egalitarian farming groups, although warfare undoubtedly increases when such groups develop into stratified chiefdoms or states.

Zitat:Around 7,000 years ago - all the way back in the Neolithic - something really peculiar happened to human genetic diversity. Over the next 2,000 years, and seen across Africa, Europe and Asia, the genetic diversity of the Y chromosome collapsed, becoming as though there was only one man for every 17 women.

Now, through computer modelling, researchers believe they have found the cause of this mysterious phenomenon: fighting between patrilineal clans.

Drops in genetic diversity among humans are not unheard of, inferred based on genetic patterns in modern humans. But these usually affect entire populations, probably as the result of a disaster or other event that shrinks the population and therefore the gene pool.

But the Neolithic Y-chromosome bottleneck, as it is known, has been something of a puzzle since its discovery in 2015. This is because it was only observed on the genes on the Y chromosome that get passed down from father to son - which means it only affected men.

This points to a social, rather than an environmental, cause, and given the social restructures between 12,000 and 8,000 years ago as humans shifted to more agrarian cultures with patrilineal structures, this may have had something to do with it.

In fact, a drop in genetic diversity doesn't mean that there was necessarily a drop in population. The number of men could very well have stayed the same, while the pool of men who produced offspring declined.

This was one of the scenarios proposed by the scientists who penned the 2015 paper.

"Instead of 'survival of the fittest' in a biological sense, the accumulation of wealth and power may have increased the reproductive success of a limited number of 'socially fit' males and their sons," computational biologist Melissa Wilson Sayres of Arizona State University explained at the time.

Tian Chen Zeng, a sociologist at Stanford, has now built on this hypothesis. He and colleagues point out that, within a clan, women could have married into new clans, while men stayed with their own clans their entire lives. This would mean that, within the clan, Y chromosome variation is limited.

However, it doesn't explain why there was so little variation between different clans. However, if skirmishes wiped out entire clans, that could have wiped out many male lineages - diminishing Y chromosome variance.

Computer modelling have verified the plausibility of this scenario. Simulations showed that wars between patrilineal clans, where women moved around but men stayed in their own clans, had a drastic effect on Y chromosome diversity over time.

This means that warring patrilineal clans are the most likely explanation, the researchers said.