The June 5th edition of Science carries a feature which includes two anthropology papers discussing aspects of the late Palaeolithic, one of which examines the role altruism might have played in the evolution of hunter/gatherer (forager) societies as an alternative to warfare, whilst the other suggests that early Upper Palaeolithic cultures such as the Aurignacian may in part have sprung up as a result of increased population density. Both papers are reviewed by Ruth Mace from University College, London, who also appears in the June 5th Science podcast. Here’s her written introduction in Science…
“Unlike other animals, humans cooperate with nonrelatives in coordinated actions, decorate their bodies, build complex artefacts (useful or otherwise), talk, and divide themselves into linguistic groups. To understand the evolutionary basis of such behaviors, anthropologists must consider not only issues connected to social evolution in animals, but also the implications of the possible coevolution of genes and culture.
Two articles in this issue examine aspects of human social evolution: On page 1293, Bowles (1) investigates the origins of altruism toward one’s own social group, while on page 1298, Powell et al. (2) study the emergence of cultural complexity. Based on empirical evidence and modeling, both studies suggest that the demographic structure of our ancestral populations determined how social evolution proceeded.”
At least one anthropologist, Richard Klein of Stanford University, vehemently disagrees, ascribing instead a genetic change in the human brain around 50,000 years ago to account for a perceived set behavioural changes that have been cited as being for example, a significant factor in the extinction of the Neanderthals at the expense of anatomically modern humans.
Here are the abstracts to the two papers, the second of which appears in full at Science…
Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors? by Samuel Bowles
Since Darwin, intergroup hostilities have figured prominently in explanations of the evolution of human social behavior. Yet whether ancestral humans were largely “peaceful” or “warlike” remains controversial. I ask a more precise question: If more cooperative groups were more likely to prevail in conflicts with other groups, was the level of intergroup violence sufficient to influence the evolution of human social behavior? Using a model of the evolutionary impact of between-group competition and a new data set that combines archaeological evidence on causes of death during the Late Pleistocene and early Holocene with ethnographic and historical reports on hunter-gatherer populations, I find that the estimated level of mortality in intergroup conflicts would have had substantial effects, allowing the proliferation of group-beneficial behaviors that were quite costly to the individual altruist.
Late Pleistocene Demography and the Appearance of Modern Human Behavior by Adam Powell, Stephen Shennan, and Mark G. Thomas.
The origins of modern human behavior are marked by increased symbolic and technological complexity in the archaeological record. In western Eurasia this transition, the Upper Paleolithic, occurred about 45,000 years ago, but many of its features appear transiently in southern Africa about 45,000 years earlier. We show that demography is a major determinant in the maintenance of cultural complexity and that variation in regional subpopulation density and/or migratory activity results in spatial structuring of cultural skill accumulation. Genetic estimates of regional population size over time show that densities in early Upper Paleolithic Europe were similar to those in sub-Saharan Africa when modern behavior first appeared. Demographic factors can thus explain geographic variation in the timing of the first appearance of modern behavior without invoking increased cognitive capacity.
With regard to the first paper, just to briefly add that I’m not exactly clear how ‘altruism’ is defined – if modern society can provide any meaningful model, it seems clear that the suggestion or perception of altruism being bestowed on a society are more common than societal acts of altruism per se. Machiavelli might not have had a direct prehistoric counterpart, but I can imagine that deceit and gullibility played just a large a part as altruistic behaviour, and if that catastrophic warfare was occasionally avoided, the survivors would stand a greater chance of sustaining community as well as allowing for the birth of future generations.
The content of the second paper is mentioned at Bloomberg, in an article ‘Ancient Art, Music Flowered as Communities, Not Brains, Grew ‘, as we see from this clipping…
“Researchers used genetic estimates of ancient population sizes, archaeological artifacts and computer simulations of social learning. They found complex skills involving abstract thinking would be passed down through generations and across groups only when populations reach a critical level, according to the study in tomorrow’s edition of the journal Science.
Increased interaction between groups, the sharing of ideas and the exchange of raw materials that led to the flowering of human culture may explain why concentrated centers of industry, such as California’s Silicon Valley, produce technological innovations, said Mark Thomas, 44, a senior author of the study and a senior lecturer at University College London in England.
“People learn from their parents or teachers in their group, and this model demonstrates you have to have a critical number of people learning to develop complexity,” Adam Powell, 28, a co-author of the study and a doctoral student at the London university. “The actual invention of all these technologies was probably very common, but was only passed on as density increased.”
As numerous studies over recent years have shown, perhaps most famously at Blombos Cave, modern humans were using coloured ochre and etching patterns into surfaces a good 40,000 years before cave painting and figurative art became much more widespread, and there is evidence from elsewhere in Africa of the use of ochre, manufacture of shell beads etc., dating back tens and even hundreds of thousands of years beforehand. Moreover, the use of fire to treat resin in the manufacture of adhesive for use in hafting tools is first known from the Neanderthals (who were probably the first to bury their dead) at around 80,000 years ago, again by moderns at around 60 kya, whilst evidence of ochre use, modification of pebbles, rocks and shells goes back to the Lower Palaeolithic. These factors indicate that the crucial components required for complex cognitive thought and lateral thinking were in place at the emergence of the first anatomically modern humans, the lifespan of the Neanderthals and quite possibly other archaic species before them.
Here’s the reaction that the second paper prompted from Richard Klein…
“Not everyone is convinced the demographic model caused the behavioral change. Richard Klein, an anthropology and biology professor at Stanford University, said the study is flawed because the examples it cites of human behavior prior to 50,000 years ago are either misdated artifacts or are open to interpretation as to their level of advancement.
“They have it wrong,” Klein said in a telephone interview. “This paper does not belong in print.” Klein is a proponent of a competing theory that attributes the development of modern human behavior to a genetic change to human brains 50,000 years ago. “These behaviors appear to have been part of a package that significantly enhanced human fitness — the ability to survive and reproduce,” Klein wrote in a study that was published last year in the journal Evolutionary Anthropology. “It is in this sense that they signal true evolutionary change as opposed to mere historical change.”
The point to make is that innovative technologies and behaviours could have been invented, forgotten and discontinued many times over during the course of the entire Palaeolithic, but because populations were sparse, largely isolated from one another, constantly on the move, and prone to dying out, passing down innovations – and even language – through many generations simply wouldn’t have been possible. Some early humans would have come up with ideas and inventions, maybe passing them on for a few or more generations, whilst many others would have led less technologically and culturally advanced lives, yet still survived perfectly adequately. This would in part have been because low population densities would have meant less competition for resources, and therefore less pressure to redesign lifestyles, lithic industries or even diet – unless of course, there was radical climate change, such as a glaciation, post-glacial melt and related large-scale faunal extinction.
With no definitive evidence of the appearance of a single master-gene which presumably would have switched on some sort of automatic modernity module in humans, I’m more inclined to agree with elements of the population theory – it might not cover all the bases, but if people were spending increasing amounts of time in each others’ company, it seems a lot easier to imagine that over the centuries and millennia, behavioural models would noticeably change as a result of new and unexpected stresses placed upon them, and become a great deal more complex, especially once the built, or constructed environment began to emerge, notably at Göbekli Tepe and its sister sites, around 12,000 years ago.
- Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors? Samuel Bowles (5 June 2009) Science 324 (5932), 1293. [DOI: 10.1126/science.1168112]Late Pleistocene Demography and the Appearance of Modern Human Behavior Adam Powell, Stephen Shennan, and Mark G. Thomas (5 June 2009) Science 324 (5932), 1298. [DOI: 10.1126/science.1170165]
Science Podcast (5 June 2009) Science 324 (5932), 1341-b. [DOI: 10.1126/science.324_1341b]