Re: Trip to beach a milestone in human evolution: study (Oct. 17): my colleagues and I welcome this paper which happily quotes our work. In 1972 we published data which for the first time perhaps identified arachidonic and docosahexaenoic acids as determinants of brain growth and function. From comparative studies we drew conclusions linking these brain specific fatty acids with the evolution of the mammalian brain.1 Later, I recognised the implications for human evolution.2
This recognition led to several other papers,3-6 including a book7 proposing the coastal origins of humans as essential for cerebral advancement and a competitive advantage in the development of cognition. A crunch paper was on Dolphins8 in which we made the comparison with a similar body weight land based mammal, the zebra, which has 350g brain and the dolphin with 1.8 Kg.
As far as we were concerned there was no parallel example of cerebral advancement on land as all land based species lost brain weight in relation to body size as they evolved larger and larger bodies (chimps 0.45% rhinos <0.02%). Only H. Sapiens (2% 1.4 Kg) has the similar brain body weight ratio compared to small mammals like squirrels and Sykes monkeys. The only evidence of sizeable brain evolution apart from H. Sapiens is with the marine mammals, dolphins in particular but up at the top you have the sperm whale with 8 Kg brain!
Our many papers on food composition described the paucity of DHA in the land food web. And of course the richest source is the marine food web which is where the brain evolved using DHA 600-500 million years ago and still uses it today for its neurones and synapses.
That is the primate leading to H sapiens must have found an ecological niche which would have provided the limiting docosahexaenoic acid (DHA) in abundance and so maintained a harmony of brain and body growth.
The paleoanthropologists have consistently ignored or found spurious arguments against the biochemistry based coastal hypothesis. So this new evidence, not unlike the Klasies estuary shell middens in South Africa described by Parkington and others of 125 kya. Add strength to the coastal origins of humans. 9, 10
Philip Tobias (with John Parkington et al) is the only one I know who accepted the coastal/lacustrine hypothesis when he said at the Dual Congress in South Africa 1998 "We can throw the savannah hypothesis out of the window" and then in his special way crystallised the whole idea and tons of research by saying "wherever man was evolving he had to have water to drink!"
8. Williams, G. and Crawford, M. A. (1987) Comparison of the fatty acid component in structural lipids from dolphins, zebra and giraffe: possible evolutionary implications. J. Zool. Lond. 213: 673-684.
9. Klein RG, Avery G, Cruz-Uribe K, Halkett D, Parkington JE, Steele T, Volman TP, Yates R. (2004) The Ysterfontein 1 Middle Stone Age site, South Africa, and early human exploitation of coastal resources. Proc Natl Acad Sci U S A;101(16):5708-15.
10. Parkington, J.E., 1990. A view from the south: Southern Africa before, during and after the Last Glacial Maximum. In: Gamble, C., Soffer, O. (Eds.), The World at 18,000 BP: The Low Latitudes, Vol. 2. Unwin Hyman, London pp. 214–228.