Topic: Fish-Always a good bet
If Neanderthals ever shared a Thanksgiving feast with Homo sapiens, the two species may have had trouble settling on a menu.
Chemical signatures locked into bone suggest the Neanderthals got the bulk of their protein from large game, such as mammoths, bison and reindeer. The anatomically modern humans that were living alongside them had more diverse tastes. As well as big game, they also had a liking for smaller mammals, fish and seafood.
“It seems modern humans had a much broader diet, in terms of using fish or aquatic birds, which Neanderthals didn’t seem to do,” says Michael Richards, a biological anthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany and the University of British Columbia in Canada.
Such dietary differences could have played a role in the extinction of Neanderthals roughly 24,000 years ago.
“I personally think [Neanderthals] were out-competed by modern humans,” says Richards. “Modern humans moved in with different, more advanced technology and the ability to consume a wider variety of foods, and just replaced them.”
He and colleague Erik Trinkaus at Washington University in St Louis, Missouri, compiled chemical measurements taken from bone collagen protein belonging to 13 Neanderthals and 13 modern humans, all recovered in Europe. They also added data collected from a 40,000-year-old human recovered in Romania’s Oase cave.
Because our bones are constantly destroyed and rebuilt while we are alive, the atoms that make up collagen hold a record of what we’ve eaten. “When you take a sample of a bone you’re getting all those breakfasts, lunches and dinners for 20 years,” Richards says.
Measurements of the abundance of heavy isotopes of carbon and nitrogen hold the key. Marine environments contain a higher proportion of heavy carbon atoms (carbon-13) than land ecosystems, so lots of carbon-13 in the recovered collagen points to a seafood diet. Meanwhile, heavy nitrogen (nitrogen-15) tends to build up as the atom moves up the food chain, from plants to herbivores to carnivores.
High levels of heavy nitrogen can also come from a diet with lots of freshwater fish. Aquatic food webs tend to contain more steps than terrestrial ecosystems, so large fish often have higher levels of heavy nitrogen than land predators.
By comparing the relative levels of these isotopes with those of animals found nearby, researchers can sketch the broad outlines of an ancient diet, if not every last calorie.
Carbon and nitrogen isotopes suggest that Neanderthals living between 37,000 and 120,000 years ago in what are now France, Germany, Belgium and Croatia got the bulk of their protein from large land herbivores, Richards and Trinkaus conclude. Levels of heavy nitrogen in Neanderthal bones invariably exceed levels in surrounding herbivores, and tend to match levels in that period’s carnivores, such as hyenas.
Some modern humans living between 27,000 and 40,000 years ago opted for more varied diets. High levels of carbon-13 in two samples from Italy and France are evidence for a diet that probably included some marine fish or seafood.
Variety pays off
Such flexibility may explain why modern humans thrived in ancient Europe while Neanderthals perished, says Hervé Bocherens, a biological anthropologist at the University of Tübingen in Germany. “If modern humans were hunting big game, like Neanderthals, they would compete with them and deplete the resources.”
When big game were scarce, modern humans could have survived and even flourished by eating fish and smaller animals. Neanderthal populations, by contrast, probably shrank and eventually disappeared in areas from which their more limited meal options disappeared.
However, Bocherens cautions against drawing too many conclusions from 13 Neanderthal skeletons, all unearthed in northern Europe. Collagen doesn’t survive well in warmer climates, so researchers know less about the diet of Neanderthals in southern Europe and the Middle East, he says.
“There is evidence from a number of southern European sites in Portugal, Gibraltar, Spain and Italy that Neanderthals did exploit marine resources at times and, I would say, probably to a significant extent,” says Chris Stringer, a palaeoanthropologist at the Natural History Museum in London. His team recently found cut marks on seal and dolphin bones in a Neanderthal cave in Gibraltar.
Isotopes recovered from bone also ignore important sources of food that don’t contain much protein. “I’m sure they’re having vegetables,” says Richards. “But they’re not eating enough that it’s being measured.”
A new study of ancient DNA offers preliminary support for that conclusion. Neanderthals possessed a gene mutation that would have meant they couldn’t taste bitter chemicals found in many plants.
There has been speculation that this mutation, which occurs in a taste receptor gene called TAS2R38, is beneficial to humans because it makes vitamin-packed vegetables more palatable. It probably arose in the common ancestor of modern humans and Neanderthals more than a million years ago. The gene encodes a receptor that detects a chemical called phenylthiocarbamide, which is closely related to compounds produced by broccoli, cabbage and Brussels sprouts.
If vegetables weren’t part of the Neanderthal diet, the species would probably have lost the non-tasting mutation, says Carles Lalueza-Fox, a geneticist at the Institute of Biological Evolution in Barcelona, Spain, whose team sequenced TAS2R38 in 39,000-year-old DNA from a Neanderthal femur recovered in the El Sidrón cave in north-west Spain.
This Neanderthal’s DNA tested positive for tasting and non-tasting versions of TAS2R38, suggesting he or she boasted copies of both alleles of the gene – and with it the ability to taste bitter foods. The presence of the non-tasting allele in this individual suggests it may have been beneficial to some Neanderthals.
“It doesn’t mean they were eating Brussels sprouts or cabbage but it could be similar vegetables,” Lalueza-Fox says.
12 August 2009
by Ewen Callaway
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