To fish or not to fish

This summer I pointed to an article about the FwJj20 locality at Koobi Fora, which provides the earliest known evidence of systematic fish exploitation in the archaeological record (“The fish of Koobi Fora”). I mentioned that another interesting paper in the journal was worth discussion, by José Joordens and colleagues, titled “A fish is not a fish: Patterns in fatty acid composition of aquatic food may have had implications for hominin evolution”.

The article takes a nutritional ecology approach, examining the empirical question of whether African lake fish have similar nutrients as Indian Ocean marine fish, focusing particularly on fatty acids, DHA and EPA. They find some differences between the oceanic and lacustrine fish in these resources, but focus most of their essay upon a review of the literature on the nutritional value of fish in freshwater and marine environments and their possible importance in human evolution.

There are many good things in this review. I have written about aquatic resource use many times before, including Joordens’ work. I think that aquatic resource use shows something very important about the behavioral and dietary flexibility of early Homo.

I commented in 2009 on the FwJj20 locality (“Fishy story from Koobi Fora”). , emphasizing that the demonstration of aquatic resource use is very different from showing that a lack of aquatic resource use is a

I accept that reptile and fish meat may be nutritionally desirable. The question is whether they caused the increase in brain size associated with Homo. One way to read that hypothesis is as Lamarckism, which is simply wrong (Larry Moran has commented on that topic). I don't think that any paleoanthropologists are seriously Lamarckist, but some need to be more careful how they describe the relationship of fitness and diet.

Joordens and colleagues provide an important corrective to some of the earlier claims about aquatic resources. In doing so, they bring the comparative method to the issue of aquatic resources:

Further, we feel that it is essential to distinguish between a triggering, facilitating and/or driving role of aquatic resource exploitation. If aquatic resource exploitation had been the major driver for hominin brain expansion, we would expect that this mechanism would have led to a similar enormous brain expansion in other animal lineages such as carnivores foraging in aquatic ecosystems. Indeed, considerable brain expansion has occurred in cetaceans (particularly in Delphinidae), but it took place millions of years after adaptation to a completely aquatic lifestyle and could not be causally connected to an aquatic lifestyle (Marino, 2007 and Xu et al., 2012). In extant herpestids, mustelids and procyonids, the species that eat aquatic prey have the largest absolute brain sizes of their families (Shabel, 2010), but these increases in brain size do not reflect an explosive brain expansion and increase in cognition such as is seen in the human lineage (e.g., Roth and Dicke, 2005). This suggests that while aquatic resource exploitation by hominins may have triggered and/or contributed to initial moderate brain growth, one or more additional factors are required to explain the extreme events in brain growth and cognition in the hominin lineage.

This is a very important perspective on brain evolution. Certainly, larger brains have nutritional requirements. But did particular foods “trigger” the evolution of the brain, did they “facilitate” brain evolution, did they “drive” brain evolution? Were dietary changes necessary for brain evolution, or sufficient for it? Or neither?

Taxonomic breadth shows behavioral flexibility. In my opinion, dietary flexibility is a more important adaptive change than fish nutrition alone could be. Again, from my 2009 post:

Aquatic animals aren't important because of their sheer numbers, but because they tell us about the flexibility of foraging behavior. Living hunter-gatherers eat turtles and reptiles when they can, and because they are usually small food packages, they often eat them where they find them instead of returning to a base camp first. Hunter-gatherers are flexible in what they eat and where they eat it. FwJj20 is showing at least a substantial taxonomic flexibility in the meat-eating of early Oldowan hunters.

Too many scientists focus only on the “supply side” of brain energetics, emphasizing that a high-quality food source with abundant protein and fat is necessary to grow and fuel a brain. All other things being equal, an increase in the supply of food will reduce the force of selection on brain size. Understanding an evolutionary change in a trait requires us to examine the correlation between that trait and survival or reproduction.

Stone tool manufacture and tool-aided meat exploitation, starting by 2.6 million years ago, predate any substantial evidence for brain expansion by a half million years or more. Brain size hopped from an australopith value less than 500 ml up to around 600 ml in Homo habilis and early Homo erectus, and up to around 800 ml in later Homo erectus. Those changes have no obvious archaeological correlate. The later, massive increases up to a human brain size of 1350 ml or higher also have no obvious archaeological correlates – but more important, as Joordens and colleagues point out, they have no obvious dietary correlates.

The literature on aquatic resource use, with exceptions like Joordens and colleagues’ work, seems to assume that all of human evolution happened on East African lakeshores. Sure, the hominin assemblages of Kenya, Tanzania, and Ethiopia are embedded in sedimentary layers that represent river, marsh or lakeshore deposits. But nobody’s talking about the giant catfish eaten by early Homo at Swartkrans because there aren’t any. Looking more broadly, occurrences of Early Pleistocene Homo stretch from South Africa to Spain to China and Java, and include some instances with good evidence of aquatic resource use (Trinil, Gesher Benot Ya’aqov, El Kherba) and some without (Dmanisi, Sima de Elefante, Drimolen).

We have barely begun to sample other parts of Africa that lack the long lacustrine sedimentary exposures of the Rift Valley. Homo erectus or species substantially like it had a widespread distribution after 1.8 million years ago, and were essentially unknown before that time. The first occurrence of H. erectus may be Dmanisi, or Swartkrans, or even Mojokerto – any two of which represent a greater ecological and geographic distance than separates the entirety of the hominin fossil record before 1.9 million years ago. We have a lot of searching to do.

References:

Joordens, JCA, Kuipers RS, Wanink JH, Muskiet FAJ. (2014) A fish is not a fish: Patterns in fatty acid composition of aquatic food may have had implications for hominin evolution. Journal of Human Evolution doi:10.1016/j.jhevol.2014.04.004