New Scientist: Seafood gave us the edge on the Neanderthals
- From: rmacfarl <rmacfarl@xxxxxxxxxxxxxxxx>
- Date: Fri, 14 Aug 2009 04:05:47 -0700 (PDT)
[shakes head, mutters something about affirming the consequent]
http://www.newscientist.com/article/dn17595-seafood-gave-us-the-edge-on-the-neanderthals.html?full=true
* 12 August 2009 by Ewen Callaway
* For similar stories, visit the Food and Drink and Human
Evolution Topic Guides
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.
Prehistoric menu
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.
Telltale atoms
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.
Even other modern humans from a similar period that lived further
inland seem to have enjoyed a more diverse menu. Unusually high levels
of nitrogen-15 in their bones point to freshwater fish as an important
source of food, Richards says.
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.
Palatable veg
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.
Journal references: Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.0903821106
Biology Letters, DOI: 10.1098/rsbl.2009.0532
.
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