When Pliny the Elder commented, Ex Africa semper aliquid novi, (Out of Africa always something new), in 79AD, he was talking of African animals, and he was quoting Aristotle’s book on natural history, written 2,300 B.C. (Mayell, 2003)
Archaeologists could well make the same remark, in reference to just one animal: Homo. Africa, at each throw of the genetic dice, turned up hominin after hominin until it came to us – but the party didn’t stop with the first anatomically modern humans around 195 kya at Omo Kibish and Herto, Ethiopia. It was in Africa, as McBrearty and Brooks, showed in their paper The Revolution That Wasn’t, published 2000, that each single component of fully modern human behaviour evolved, whether harpoon, microlith and compound tool, or symbolic expression through hatching of ochre. I argue that during this same period, the Middle Palaeolithic, anatomically modern humans, H. sapiens, evolved a cunning new biological twist to accompany all this cunning new cultural stuff. I think that during the Middle Palaeolithic Africa dialed up our potential to lay down astounding amounts of body fat, which in turn led to increased survivability in the Levant and Eurasia after recovery from the H5 Heinrich Event.
We humans are fat, fat, fat, even when we’re skinny, compared to other primates and even to other mammals. In my earlier post, The Fats of Life, I concluded that our fattiness, and high sexual dimorphism in body fat percentage, must confer an adaptive advantage, and I’ve presented evidence that reproduction costs bear very heavily on women, who use this fat to fuel pregnancy and lactation.
There’s little evidence to show when this fattening ability came into our lineage; Leslie Aiello et al suggest that the tendency arose during the Homo erectus period, when there was a sudden increase in our body size (2002: 552). It was in this period that we probably started cooking, grew our brain, and shrank our gut. We may also have started talking at this time, and we may have lost our fur then. Caroline Pond presents evidence that other primates, notably the orangutan, have some ability to pack a paunch. Other plump animals lay down their fat along the back, which is why farmers pinch their cattle and sheep around the root of the tail to assess their condition. Only primates lay down their fat in front – Pond suggests that it may be a form of sexual signalling indicating good body condition. For primates, the belly is often on view so we can strut our stuff effortlessly (Pond 1998: 42-45).
My point: we were probably preadapted to fattening under the right conditions. I argue that these conditions arose in East Africa during the Middle Palaeolithic while Neandertals ruled the Levant and then disappeared into the dust of eternity: between 75 and 50 kya. I’m picking on East Africa because it’s almost certainly the birthplace of hominids, hominins, and H. sapiens.
This table is adapted from information provided in my Anthropology 128 class, Fall 2012, by Professor Lisa Maher.
Later sapiens could well have recolonized the Levant from East Africa, and the difference in behaviour and economy after only 30,000 years, a blink in our evolution, is striking. Something was going on during Marine Isotope Stage 4 that catapulted us into a new paradigm.
What was happening in East Africa during MIS 4?
While the degree of the effects of the Mount Toba supervolcano eruption are debated, there is consensus that a 6-10 year volcanic winter set in that affected the entire world, lowering average temperature, and probably reducing the amount of sunlight that reached Earth’s surface because of gigantic ash clouds and emission of aerosol gases. (Wikipedia: Toba) East Africa, however, was probably buffered from the worst effects, becoming somewhat colder and drier, but not as markedly as the Levant (Maher 2012). Also, its position on the Equator would maximize its solar gain. However, less light and less water would have borne hardly on forests, so grasslands would have expanded as forests shrank.
Another point in its favour: East Africa does not have the geographic circumscription of habitable zones characteristic of the Levant. Humans would have been able to migrate, following the food, whether plant or animal, as well as exploit both forest and grassland. However, game herds may well have shrunk during this time, in lockstep with the diminishing productivity of the plants on which they feed, forcing humans to start exploiting their environment more intensively.
Small fast prey like rabbits and birds need different hunting weaponry, and new technology might well be needed to extract the maximum nourishment from plant foods. Tubers or seeds might need to be crushed or pounded, knives might be in demand for peeling and slicing, and perhaps new cooking methods might have to be devised. Of interest in this regard is the finding of Phillipson et al. that “the heavily worn grindstones” found in the Nile Valley had been used to process the tubers of Cyperus rotundus, commonly known as wild nutgrass , thus warning against the assumption that grindstones equal grain (147, 148). According to Wikipedia, these 1″ long tubers are somewhat bitter, but edible, and are very rich in minerals and vitamins. They also have medicinal properties (Wikipedia: Cyperus rotundus).
Necessity is the mother of invention: with the rapid onset of bad climate (within 3 years of the Mount Toba explosion, according to the Wikipedia article referenced above), humans, particularly women, would have had to turn to other foods. Leaves and fruits were scarcer. What’s a hungry human to eat? What about tubers?
Freeliving chimpanzees, who make digging tools to grub them out, eat tubers (Kiderra 2007). The great Bob Brain claims that australopithecines were routinely extracting tubers at Swartkrans, South Africa, around 1 million years ago (Vincent 1985:131). For some nice pictures of this famous site: http://swartkrans.org/history-of-swartkrans/. Probably humans have been eating tubers all along. Forests are not prolific tuber producers; in Tanzania, forest produces 0.5 tonnes-hectare of tubers, while savanna produces a bounty of edible bulbs – ranging from 5 – 2,000 tonnes/hectare, depending on species and local conditions, with only pigs and porcupines as competitors. These bulbs can be eaten raw as well as cooked, unlike grains. Anne Vincent, whose work I am citing here, says that one hectare of savanna produces enough tubers to feed three families for 148 days (1985: 139). Tubers are more reliable than grains, and can be left underground until needed, without deterioration in quality, while they regenerate faster than cereals.
Tubers are a rich source of carbohydrate, with varying proportions of starch and sugar. Gary Taubes, in his intensively researched book Good Calories, Bad Calories, argues persuasively that the prime driver of fat deposition is carbohydrate (see summary p454). This is certainly in line with the work of Leslie Aiello and Jonathan C.K. Wells, who show that humans can metabolize only enough lean meat to meet half of their daily requirements (2002: 326), and with that of John D. Speth and Katherine E. Spielmann, who discuss the phenomenon of rabbit starvation, where tribes forced to eat lean meat as a staple, although having more than enough calories can essentially starve to death (1982: 3,4), and find that carbohydrate is non-replaceable by fat when it comes to protein sparing and muscle maintenance (6,7). Without sufficient body fat, calcium is not properly metabolised and essential vitamins are not stored (17,18).
Returning to Vincent’s work, women gathering tubers have full control of the resource, and they often eat a considerable amount of what they gather in situ. The same is true of berries and fruit . The high-status foods, meat and honey, are obtained and controlled by men, who share them out according to the societal norms (1985:135). It seems probable that natural selection would favour women able to rapidly fatten on a high-carbohydrate diet, as they would reach menarche earlier (Frisch 1990; Guo 2011), be more likely to retain a pregnancy to full term, and successfully lactate for 3 – 4 years, thus weaning a child more likely to survive till puberty.
One last tempting titbit: Sarah Blaffer Hrdy says that at the beginning of the Palaeolithic our species doubled its population size only every 15,000 years. Then, starting with a single small band of hunter-gatherers sometime around 100,000 years ago, we became “newly fecund“ and the brakes came off the breeding train (1999:184). Could the reason be a thrifty gene or thrifty phenotype that allowed carbohydrate-eating women to get fat and get fertile?
Aiello, Leslie C. and Jonathan C.K. Wells. 2002. Energetics and the Evolution of the Genus Homo. Annual Review Anthropology. 31:323-38.
Frisch, Rose E. 1987. Body fat, menarche, fitness and fertility. Human Reproduction vol 2. No 6. 521-533.
Guo, Xiao Yan & J.I. Chenge Ye. 2011. Earlier menarche can be an indicator of more body fat: study of sexual development and waist circumference in Chinese girls. Biomedical and Environmental Science, 24(5). 451-458.
Hrdy, Sarah Blaffer. 1999. Mother Nature: a history of mothers, infants, and natural selection. Pantheon Books, Random House, Inc., New York, N.Y.
Kiderra, Inga. “Chimps Dig Up Clues to Human Past?” 12 November 2007. UC San Diego News Center. Accessed 7 November 2012. http://ucsdnews.ucsd.edu/newsrel/soc/11-07ChimpsDigCluesToHumanPastIK-I.asp
Maher, Lisa. 2012. Anthropology 128, Fall semester, University of California, Berkeley, USA. Class lecture notes.
Mayell, Hillary. “Out of Africa” Phrase in Use Since Ancient Greece.” 19 February 2003. National Geographic News. 7 November 2012. http://news.nationalgeographic.com/news/2003/02/0219_030219_outofafrica.html
McBrearty, S. & Brooks, A. S. 2000. The revolution that wasn’t: a new interpretation of the origin of modern human behavior. Journal of Human Evolution, 39, 453-563.
Phillipson, D. 2009. African Archaeology, Cambridge, Cambridge University Press. Chapters 4-5.
Pond, Caroline. 1998. The Fats of Life. Cambridge University Press, Cambridge, United Kingdom.
Speth, John D. & Katherine A. Spielmann. 1983. Energy source, protein metabolism, and hunter-gatherer subsistence strategies. Journal of Anthropological Archaeology, 2:1-31.
Taubes, Gary. 2007. Good Calories, Bad Calories. Alfred A. Knopf, New York, N.Y.
Vincent, Anne S. 1985. A preliminary report of tubers eaten by the Hadza of northern Tanzania. World Archaeology, 17(2):131-148.
Wikipedia. “Cyperus rotundus.” Last updated 28 October 2012. Wiki entry. Accessed 7 November 2012. http://en.wikipedia.org/wiki/Cyperus_rotundus
Wikipedia. Toba catastrophe theory. Last updated 23 October 2012. Wiki entry. Accessed 7 November 2012. http://en.wikipedia.org/wiki/Toba_catastrophe_theory