When did our ancestors become dependent on meat?

ResearchBlogging.orgFor around 30 million years the great apes have been living in the rainforest, during which time they have been adapting and evolving to that environment. However, ~14 – 10 million years ago the African environment began to change. It got drier, there was less rainfall and what rain did occur became more seasonal. All of this resulted in the vast rainforests which covered Africa breaking up, being replaced by Savannah and wooded grassland. Our ancestors were those apes who adapted to these more open environments, using bipedalism to traverse the exposed landscape and move between patches of forest.

The Laetoli footprints, made by Australopithecines traversing an open environment bipedally

Of course, our mode of locomotion would not be the only thing which had to evolve as our environment changed, our diet would’ve had to have changed as well. Gorillas mostly eat leaves and shoots whilst fruit makes up a large part of a chimps diet. Although they do supplement their diets with other food, the fact remains that they consume resources which would not be readily found in the “new” African environment. Our ancestors who began to move into that environment would therefore have had to have changed their diet.

These dietary changes eventually resulted in our ancestors becoming essentially dependent on meat. Even today it makes up a crucial part of our diet and cutting it out of our diets would likely be a death sentence, except for those select few environments where plant resources are sufficient to compensate for it (e.g. rainforests, first world supermarkets etc.). But the shift to meat is more important still, with many arguing co-operative hunting and the associated food sharing formed the foundation of modern society. And that’s forgetting the biological changes associated with eating meat.

Identifying when meat became a crucial part of our diet, rather than merely supplementary as it is in chimps, can help reveal a lot about the aforementioned consequences of eating meat. It would also provide a date for when we became true hunter-gatherers, the way all humans lived until 10,000 years ago. So how to we go about identifying such an event? The most obvious method would be to use stable isotope analysis, but unfortunately this is not always possible.

Alternatively we can remember that life is messy and imperfect and that if we become dependent on a resource then the odds are that at some point somebody will die due to a lack of that resource. Sadly, ~1.5 million years ago, a 2 year old child did just that. They suffered from a fatal case of porotic hyperostosis which resulted in bone marrow expansion, exposing their internal bone structure. Many kinds of deficiency can result in this kind of disease, including scurvy (vitamin C deficiency) and rickets (vitamin D deficiency) but they don’t produce quite the same results as in this case. Instead it would appear this child suffered from a form of anaemia caused by vitamin B-12 deficiency.

The fossil (bottom) with a modern human who lacks the disease (top)

B-12 is one of those essential vitamins which you have to ingest since it isn’t made by your body. It comes from a range of sources but those who aren’t adapted to be herbivores (since they can ferment plant matter in their guts to feed bacteria which produce) must get it from a non-herbivorous source, such as meat or insects. The researchers argue that the likely source of B-12 for this unfortunate individual was meat since we know from cut marks on bone that our ancestors were consuming meat by this point. Therefore a lack of meat caused the death of this child, indicating meat was important to our ancestors by 1.5 million years ago.

Although this evidence may seem circumstantial, the researchers point out that chimps rarely – if ever – suffer from this condition despite living of fruit for large parts of the year because of their different biology. At the very least then this find would indicate our ancestors’ body was undergoing a fairly significant change, at the most this is evidence of our ancestors starting to become modern (although further stable isotope studies of additional material is needed to remove any lingering doubts). It is somewhat fitting that this revelation should come from the sad case of a dead child, who contributes knowledge when they weren’t able to give anything else. Certainly it gives new meaning to the words Indiana Jones’ nemesis’. “Who knows, in 1000 years even you may be worth something!

Manuel Domínguez-Rodrigo, Travis Rayne Pickering, Fernando Diez-Martín, Audax Mabulla, Charles Musiba8, Gonzalo Trancho, Enrique Baquedano, Henry T. Bunn, Doris Barboni, Manuel Santonja, David Uribelarrea1, Gail M. Ashley, María del Sol Martínez-Ávil (2012). Earliest Porotic Hyperostosis on a 1.5-Million-Year-Old Hominin, Olduvai Gorge, Tanzania PLoS ONE, 7 (10) DOI: 10.1371

3 thoughts on “When did our ancestors become dependent on meat?

  1. Two and a half million. The determination and investment into the Oldowan industry suggests a heavy reliance at least – and the growing brains.

  2. “When did our ancestors become dependent on meat?”
    If meat means antelopes etc.: never (the “endurance running” hypothesis is biologically one of the most far-fetched hypotheses ever proposed).
    If meat means shell- & crayfish, yes, 2.5 Ma might be correct, in any case, probably early-Pleistocene: 1.8 Ma we find Homo fossils & tools as far apart as Aïn-Hanech (coastal floodplain in Algeria) & Mojokerto (coastal sediments on Java): it’s obvious that these people didn’t get there running over open plains (or savannas or mountains), but simply followed the coasts (and then from the coasts inland along the rivers).
    For a recent view on ape & human evolution: Human .Evol.28: 237-266, 2013:
    “The aquatic ape evolves: common misconceptions and unproven assumptions about the so-called Aquatic Ape Hypothesis”:
    While some paleo-anthropologists remain skeptical, data from diverse biological and anthropological disciplines leave little doubt that human ancestors were at some point in our past semi-aquatic: wading, swimming and/or diving in shallow waters in search of waterside or aquatic foods. However, the exact scenario—how, where and when these semi-aquatic adaptations happened, how profound they were, and how they fit into the hominid fossil record—is still disputed, even among anthropologists who assume some semi-aquatic adaptations.
    Here, I argue that the most intense phase(s) of semi-aquatic adaptation in human ancestry occurred when populations belonging to the genus Homo adapted to slow and shallow littoral diving for sessile foods such as shellfish during part(s) of the Pleistocene epoch (Ice Ages), presumably along African or South-Asian coasts.

    • Water-based resources are often rich and it seems certain that hominins exploited them, perhaps extensively. However, I am worried that we may be over-estimating their reliance on such resources given that the are often prime areas for preservation and discovery (what with rivers exposing underlying sediment through erosion and such). This could create some preservation bias, making it seem like these sites are more common than they really were.

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