Monday 3 December 2018

Word of the Day: Food-sharing




Food-sharing: then and now... (Creative Commons)

What made us human? In 1978, archaeologist Glynn Isaac suggested one possible answer: food-sharing. Early hominins, Isaac argued, 'made tools and carried food to a home base', where they would share the fruits of their hunting, scavenging, and foraging. Hominins wanted to avoid confronting menacing grassland predators. And a division of labour was developing between hunting and foraging. So perhaps it became advantageous for hunter-gatherers to take surpluses from their hunting and gathering back to a 'home base' where they could share their food with other kin relations. At least, that is Isaac's opinion. The problem is that he does not make consistently accurate predictions about the distribution of bones and artefacts in early hominid sites. Luckily, however, his hypothesis does make broadly accurate predictions about the direction of behavioural and biological evolution. The hypothesis does not agree with all existing observations, but at least it is simple and powerful. I think it is 'empirically ambiguous', as it's unclear whether it explains all observations, but 'theoretically parsimonious', as it's simple and powerful. We can only hope that further excavations of early hominin sites, dating from nearly 2 million years ago, help us to get to the bottom of these questions: (1) 'what explains the artefact and stone distributions at these ancient sites?', and (2) 'what made us human?'. 


The first food-sharer? Meet Australopithecus boisei, an early hominid. (Creative Commons)

Firstly, then, does the food-sharing hypothesis explain the distribution of bones and artefacts in early hominin sites? Isaac thinks that some archaeological sites in East Africa, where a high concentration of bones and artefacts are found, represent some of the first 'home bases', where hominins engaged in food-sharing. Isaac claims that ‘protohuman hominids’ (or 'hominins' in today's terminology) engaged in ‘food-sharing behaviour’ around home-bases. He details artefact and animal bone concentrations at East African Oldowan sites such as Kay Behrensmeyer. There, a concentration of stones and bones lends weight to the argument that protohumans ‘made and discarded their tools here’ and ‘were also responsible for the bone accumulation because they met here to share their food’ (Isaac, 1978:100). But perhaps water flow, not hominin activity, led to these artefact and bone concentrations (Potts, 2017:11). This is quite plausible, given that the Olduvai Gorge sites surround ancient water sources (Schick, 2017:802). As Binford (1983:70) contends, ‘considerable quantities of bone can be expected to occur around water sources’ regardless of hominin activity. This suggests that natural fluvial depositional processes may be responsible for the dense bone concentrations in the Olduvai beds. But only 7% of Olduvai Bed I specimens were affected by abrasion, and weathering at the 'FLK Zinj' site is even rarer (Klein, 2009; Potts, 1984). Water flow alone cannot account for these concentrations. Perhaps hominin activity can.

But Isaac’s theory also implies continuous occupation of a single site. This is implausible, for two reasons. Firstly, the concentration of Olduvai sites around water-holes makes continuous occupation by hominins seem very unlikely. ‘Actualistic studies’ of modern water holes indicate ungulate presence during the day but predation during the night, making water-holes dangerous places indeed to rest when the sun goes down over the savannah (Binford, 1983:66-67). This is the reason modern hunter-gatherers (e.g., the Botswanan San of the Kalahari Desert) rarely locate their camps next to water sources (ibid.:68). This makes it more likely that the water sources were simply locations of ‘natural deaths’ of animals, ‘predatory kills’, ‘hyenas gnawing’, and fluvial depositional factors (ibid.:68-70). Perhaps a combination of these ‘natural’ (non-hominin) factors led to the observed concentrations in Olduvai and more recent (dating to 200-400 ka) waterhole sites like Elandsfontein. Also, computer simulations indicate the likelihood of bases being used as ad hoc energy-saving strategies rather than as permanent eating and sleeping locations (Potts, 1984:345). Early hominins might have deposited stones there for future usage, but it is unlikely they used these sites as 'home bases' for sleeping. So it is unlikely that these sites were Isaac's continuously occupied home bases. Food-sharing alone cannot explain the concentrations at these sites. Isaac's hypothesis, then, is ambiguous when it comes to explaining bone/artefact concentrations at early hominin sites.

Secondly, does the food-sharing hypothesis (partly) explain behavioural and biological evolution? I think it does, for a couple of reasons. First, the biological origins of modern humans may be partly sought in the possible dawn of food-sharing nearly 2 million years ago. Meat-eating, perhaps around home bases, may have played a role in leading to increasing brain size (Aiello & Wheeler 1995). The cut marks and fracture patterns of ‘large mammal carcasses’ reinforce the notion that home bases were locations for systematic butchery (Bunn, 1986). This led to our ancestors' consuming high-nutrient animal fat and protein which, over time, simplified our digestive tracks and freed up metabolic energy for enlarging the brain (Toth & Schick, 2018:65). Perhaps our collective meat-eating around home bases led to 'physical selection pressures' which promoted brain enlargement (Isaac, 1978:108). Food-sharing contributed to certain long-term biological changes, through collective meat-eating, socialising, and stone-manufacture around home bases.

Food-sharing also explains other human 'social' characteristics. Early hominin sociality is particularly well explained by Jones’s (1984) concept of ‘tolerated theft’. When a latecomer arrives to a hominin group devouring a carcass, early hominins may have begun to 'tolerate' this latecomer's 'theft' of their scavenged find.  They allowed latecomers to seize some of the catch for themselves. Then, when they were 'late' to a kill or scavenge, they too demanded some share in the food. So a system of tolerated theft and reciprocal altruism developed - presumably around a home base. This reciprocity was a dynamo of behavioural evolution (Trivers, 1971) and modern human reciprocity (Fukuyama, 2014:88-89; Mauss, 1925). What does it mean to be human? It means to reciprocate: 'you scratch my back, I'll scratch yours', but in a way that means you have to think about future debts and obligations. This need to ‘calculate’ future ‘contingencies’ of food-procurement would select for more ‘logical’ cognitive capabilities (Isaac, 1978:106). Food-sharing contributed to more complex modes of reciprocity than is found in other primates. We think about how much food we need to feed the entire home base - not just ourselves. So food-sharing might have developed both more complex reciprocity and enhanced cognition. The food-sharing hypothesis helps to explain many ‘human’ characteristics, from brain enlargement to reciprocal gift-giving. This helps to explain human phenomena from Albert Einstein to feasting and gift-reciprocating at Christmas time.

Overall, the food-sharing hypothesis doesn't fully explain the bone/artefact distributions in East and South African sites. But Isaac’s hypothesis provides a simple and powerful explanation of some long-term trends in human biological and behavioural evolution. But we might need to wait for a while until further excavations, observation of hunter-gatherer activity, and dating methods rigorously test Isaac's and others' hypotheses. The food-sharing hypothesis has not so far proved as empirically watertight as it is theoretically parsimonious. Only time will tell whether the data of pre-history is better explained by competing hypotheses. As of yet, the food-sharing hypothesis has fared surprisingly well in relation to its competitors—particularly in the light of its empirical shortfalls. At least Isaac has got us thinking about one of the greatest questions of all: what made us human?

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