By Aaron Jonas Stutz
We are omnivores. That is our evolutionary heritage. We’re more intensely omnivorous than any other biological species. Through diverse cultural approaches, human societies extract plant and animal resources alike–some wild and terrestrial, many more more wild and aquatic, most terrestrial and domesticated. Human populations do so at a rate that is terrifying in comparative ecological perspective. Our omnivorous diets have fed our current, still-growing biomass. (A variety of back-of-the-envelope estimates conclude that our biomass, including all 7.4ish billion of us alive today, exceeds what all of the trillions of ants weigh.)
The ecological advantage of omnivory comes into focus when we consider what kinds of plants we eat most. And it’s not so much the whole plant organism, as it is the plant tissues we prefer. Sure, certain leaves and stalks and roots provide fiber, minerals, vitamins, analgesics, or anti-inflammatory components. But we tend to go for those tissues that help the plant grow, because these are much richer in starch or fats, poorer in fiber: seeds, nuts, fruits, and edible roots and tuber bulbs. If we can gather these plant parts, we can pack a lot of calories into a few bites. Kaplan et al. (2010: 31) emphasize that–even before domestication, farming, cities, industrialization or globalization–our omnivorous niche was well-constructed by generations of hunter-gatherers:
Although human foragers have lived in virtually all the world’s terrestrial habitats, they always occupy one extreme feeding niche, eating the highest quality, most nutrient dense, and difficult to acquire plant and animal foods in their environment.
We get these “nutrient dense” animal and plant tissues thanks to an integrated adaptive system that evolved over millions of years. We cooperate to search for and get food, we use tools to leverage the rich tissues from the wider biosphere into our grasp, we transport the food, we prepare it to make it more digestible, and we share it. And we repeat the whole cycle. While we know the big picture pattern–our last common ancestor with chimpanzees and bonobos, around 7 million years ago, was a lot less omnivorous than we are today–it’s hardly clear where and when our more recent ancestors in the genus Homo (including H. erectus, Neanderthals, anatomically modern humans) got so omnivorous.
One recent clue about the evolution of human omnivory comes from the Gesher Benot Ya’akov (GBY) site in northern Israel. Located along the upper Jordan River, GBY is a Lower Paleolithic site dating to ca. 780,000 years ago. Its remarkably stable waterlogged setting has favored the preservation of fresh and charred plant food remains, along with delicate animal parts, such as crab shells (Goren-Inbar, 2011; Melamed et al., 2016). It is one of the few Paleolithic sites of any age that has preserved such a full range of the foods–from tiny seeds to the large deer–that omnivorous hunter-gatherers captured and brought back to a transiently occupied camp site. Most paleoanthropologists would classify the inhabitants of those ancient camp sites at GBY as members of Homo erectus populations. The documentation of diverse, nutritionally rich plant tissues–including seeds, nuts, and starchy “underground storage organs”–surprised some of my colleagues, who expected Homo erectus to have evolved as a hunter first. Under this hypothesis, high-fiber, low-nutrient plants would have been gathered and eaten as fall-back or filler foods. But the plant foods at GBY are not only varied. They are really nutritionally rich.
This finding suggests some key questions. How far did the hunter-gatherers travel from and back to camp to obtain these foods. Were they just a short walk away? Or were they the result of hours-long searches? A related question is, how much of the food was consumed directly or adjacent to the plant on which it grew, and how much was carried back to the residential/sleeping camp? (Some of the camp stays at GBY involved controlled use of fire, for night time warmth, protection, or cooking.) These questions are important because they highlight the fact that omnivorous human foraging could have gradually evolved, along a spectrum of eat-as-you-go, on one end, to logistically-forage-from-central-place, on the other. The setting of GBY suggests that inhabitants may have traveled for hours to get stone materials for tool making (Goren-Inbar, 2011). But they probably foraged for rich wild plant foods close to camp, before moving on to the next foraging patch (Melamed et al., 2016). GBY is relatively closer to the eat-as-you-go pole.
Our current project investigates a site located downstream from GBY, at Mughr el-Hamamah (MHM). Located in Jordan’s Ajloun Governate, MHM is both smaller and much more recent. I have previously blogged about our results of the radiocarbon dates on charcoal from MHM. Falling into the period 45-39,000 years ago, the hunter-gatherer camp traces at MHM include characteristic Early Upper Paleolithic stone tools. A small cave perched above a steep valley slope, MHM would have provided shelter at the ecotone between the Jordan Valley bottom (warm year-round, low precipitation, but abundant lake and river water) and the Transjordanian Plateau (higher elevation Mediterranean foreset). Plant and animal resources brought to MHM would have been transported to the cave over more significant distances. MHM is closer to the central-place-foraging pole. Our colleague Jamie Clark’s results show that gazelle, fallow deer, goat and ibex would have been important animal foods for the Early Upper Paleolithic inhabitants. Eleni Asouti and Chantel White have shown that the charred plant remains preserve intact botanical structre on the microscopic level. We expect that new excavation–utilizing small-batch processing methods to recover plant remains very carefully–can reveal seeds and nut shells, in addition to wood charcoal. Thus, we hope to learn about what may have changed in plant food exploitation, as gathering gradually shifted from eat-as-you-go to central-place-foraging. We have hypothesized that this shift may be part of the cultural adaptations associated with the colonization and population expansion of anatomically modern humans (AMH, that is, those Stone Age African people whose populations grew, dispersed out of Africa, with some individuals interbreeding with some Neandertals and other Eurasian locals, before mainly replacing them through recurrent dispersals and natural selection). To be sure, AMH expansion took place in western Eurasia just as Mughr el-Hamamah was being used as a mobile camp site. And not just any camp site. MHM is located right in the richest, most diverse ecological corridor just outside of Africa. A nice place for omnivorous foraging.
Our Summer 2017 fieldwork is scheduled for July, involving myself, Liv Nilsson Stutz, and archaeobotany specialist Chantel White. With support from the Wenner-Gren Foundation for Anthropological Research, we are also making a crowdfunding push to fund our research budget. As of 6 am EDT on 15 March 2017, you can visit https://experiment.com/paleoplants or http://bit.ly/2nnAaGY+ to learn more about our crowdfunding campaign and research plans. We hope that you choose to support our research. I will be updating this site frequently, writing about related research, ideas, and results that our collaborative team is presenting at conferences or preparing for publication.
Goren-Inbar, N. (2011). Culture and cognition in the Acheulian industry: a case study from Gesher Benot Yaʿaqov. Philosophical Transactions of the Royal Society B: Biological Sciences, 366(1567), 1038–1049. https://doi.org/10.1098/rstb.2010.0365
Kaplan, H., Gurven, M., Winking, J., Hooper, P. L., & Stieglitz, J. (2010). Learning, menopause, and the human adaptive complex. Annals of the New York Academy of Sciences, 1204(1), 30–42. https://doi.org/10.1111/j.1749-6632.2010.05528.x
Melamed, Y., Kislev, M. E., Geffen, E., Lev-Yadun, S., & Goren-Inbar, N. (2016). The plant component of an Acheulian diet at Gesher Benot Ya‘aqov, Israel. Proceedings of the National Academy of Sciences, 113(51), 14674–14679. https://doi.org/10.1073/pnas.1607872113