Freshwater fish are a major part of the diet of many peoples around the world, but it has been unclear when fish became a significant part of the year-round diet for early humans. Chemical analysis of the protein collagen, using ratios of the isotopes of nitrogen and sulphur in particular, can show whether such fish consumption was an occasional treat or part of the staple diet.
     The isotopic analysis of the diet of one of the earliest modern humans in Asia, the 40,000 year old skeleton from Tianyuan Cave near Beijing, has shown that at least this individual was a regular fish consumer. Michael Richards of the Max Planck Institute for Evolutionary Anthropology explains "Carbon and nitrogen isotope analysis of the human and associated faunal remains indicate a diet high in animal protein, and the high nitrogen isotope values suggest the consumption of freshwater fish." To confirm this inference the researchers measured the sulphur isotope values of terrestrial and freshwater animals around the Zhoukoudian area and of the Tianyuan human.
     Since fish appeared on the menu of modern humans before consistent evidence for effective fishing gear appeared, fishing at this level must have involved considerable effort. "This analysis provides the first direct evidence for the consumption of aquatic resources by early modern humans in China and has implications for early modern human subsistence and demography", says Richards.
     Other researchers have theorized that fish consumption may have helped humans grow bigger brains, though it's also thought that the introduction of meat protein from land animals into the human diet, perhaps 2 million years ago, was an important factor, too. (Other factors, such as sheer survival needs driven by environmental catastrophe, may have fueled brain growth, too.) Regardless, the shift to more fish in the human diet, as found in the new study, likely reflects greater pressure from an expanding population at the time of modern human emergence across Eurasia, Richards and his colleagues said in a statement.

Sources: EurekAlert!, GEN News, LiveScience (7 July 2009)