Testing the hairs of ancient people to determine their diet!
[www.vegetarian1.net]
Just a strand of hair can dish the dirt on closet carnivores or reveal
what an Egyptian mummy liked to eat. Stephanie Pain gets to the root
of the mattter

Are you a glutton for hamburgers? Or more of a fish-and-chips person?
Perhaps you're a vegan but sometimes can't resist an egg. Whatever
your dietary secrets, Steve Macko will find them out - and all he
needs is a tiny lock of your hair. Each strand contains telltale signs
of your favourite foods, says Macko, an organic geochemist at the
University of Virginia in Charlottesville. "They are pumping in from
your breakfast right now." And once they are there, they're fixed - a
lasting record of past meals.

Your eating habits may be no secret, but for archaeologists the
chemical signatures in hair are a great untapped resource, packed with
clues to ancient lives. Remains of food found at archaeological sites
may be a misleading indicator of diet, because some things are more
perishable than others. But excavated bodies, particularly mummies,
often have a luxuriant head of hair. And Macko's latest tests show
that ancient locks can show what their owners ate, perhaps thousands
of years ago, just as reliably as your hair says what you ate last
week.

Fruits of the sea

For archaeologists, diet is not just a question of what people had
for dinner. "If you know what people ate, you know how they spent a
vast amount of their time," says Tamsin O'Connell, a chemist at the
Research Laboratory for Archaeology and the History of Art at Oxford
University. "If they ate only mussels or fish, you can say they were
fishermen. If they ate barley and wheat, you have farmers."

"You are what you eat," says Macko. And hair, made of a protein
called alpha keratin, reflects that as much as any other tissue. The
chemical signatures that allow Macko and his colleagues to see what
people have eaten are provided by stable isotopes of carbon, nitrogen
and sulphur, present in the amino acids that make up keratin. In
nature all three elements exist as a mixture of stable forms. The
light forms - carbon-12, nitrogen-14 and sulphur-32 predominate. The
heavier isotopes, burdened with extra neutrons, are here in tiny, but
measurable, amounts.

The proportion of heavy isotopes in food depends on where it came
from and its "trophic level" - its position in the food chain. In the
case of plants, it also depends on the biochemistry of photosynthesis.
"We cannot tell what kind of bread a person ate but we can determine
if they ate grains, or meat or fish or vegetables. There is a great
deal we can explain about a person's diet through hair," says Macko.

To prove the point, Macko and his colleague Michael Engel, a
geochemist at the University of Oklahoma, analysed hair from some of
their undergraduate students. Burning tiny samples of hair from each
at 1000 °C or more generates a mix of gases, which can be separated by
a gas chromatograph and analysed in a mass spectrometer, which
measures the amount of each isotope.

The amount of carbon-13 indicates broadly what sorts of plants the
students have eaten. When plants manufacture sugars during
photosynthesis, they use one of two sets of chemical reactions, driven
by different enzymes. The reactions in C3 plants - which make up most
of the world's species - discriminate against the heavy isotope and
end up with hardly any carbon-13 in their tissues. C4 plants - a
specialised group that includes important crops such as corn (maize),
sorghum, millet and sugar cane - use the two isotopes in proportion to
their concentration in the air. These carbon signals pass up through
the food chain so that hair from people who eat a lot of corn or
corn-fed animals will be higher in carbon-13 than hair from people who
eat more wheat, or animals fed grass and hay.

The nitrogen signature distinguishes vegetarians from meat-eaters. At
each step up the food chain, from plants to herbivores, to omnivores
and carnivores, the nitrogen-15 signal increases by a small but
constant amount. "No one yet knows why, but it does," says O'Connell.
"It has to do with the way metabolic processes deal with nitrogen. "
Vegans have the lowest levels of nitrogen-15. Vegetarians who eat eggs
and milk are "pseudo omnivores" in terms of their nitrogen signature,
and enthusiastic meat eaters will have a much higher level of
nitrogen-15. People who eat a lot of fish have the highest levels of
nitrogen-15. That is partly because algae, which are at the base of
the marine food chain, have more nitrogen15 in their tissues than land
plants, but mostly it reflects the longer food chains in the sea.

Large amounts of sulphur-34 in hair also reveal seafood eaters.
Bacteria in the sea that produce hydrogen sulphide discriminate
against the heavy isotope, so when the gas eventually escapes from the
water, the ocean is left richer in sulphur34. Meanwhile the fighter
isotope rains out over the land, altering the balance of isotopes
available to terrestrial plants.

Macko and Engel were not surprised to find a huge variation in
isotope signatures in their students' hair. The variability is a sign
of today's "supermarket diet". "There are lots of different foods and
lots of different eating habits," says Macko. If you plot the
students' combined carbon and nitrogen signatures on a graph, they
form a widely scattered cluster characteristic of omnivores with lots
of foods to choose from (see Diagram, p 36).

A few stood out from the crowd. One was clearly a keen carnivore,
with a nitrogen signal that put him high up the food chain. He also
had more carbon-13 than his classmates, suggesting that the animal
that provided his meat lived on a diet of C4 plants. He turned out to
be a member of the college baseball team who ate almost nothing but
burgers - made with meat from corn-fed cattle. Another student stood out
for her high nitrogen-15 signal and relatively low carbon-13 - a
combination that made her a top carnivore, but not one eating corn-fed
meat. This student came from a family which ate a lot of fish. After
six months away from home, her signature fell into line with the rest
of the class.

And then there was the vegan. Or was she? "Her signal was odd," says
Macko. It was too rich in nitrogen-15 for someone so close to the
bottom of the food chain. "Then she owned up to eating the odd slice
of Virginia ham," says Macko. "Our data were telling the truth."

Macko reckoned that if he could pick out the food foibles of his
students from their isotope signatures, then it ought to be possible
to predict what long-dead people had been eating from samples of their
hair. Archaeologists have hunted for clues to ancient diets among the
stable isotopes of bone collagen. But even under the best conditions,
says Macko, collagen suffers from decay and weathering after death.
The method of extracting collagen is also difficult, and means
destroying sizeable amounts of bone. "For archaeologists, parting with
bones is a big deal," says Engel. "But who cares about a strand of
hair?"

Macko and Engel believe that hair is a more reliable source of
information than collagen. Although hair is not always present at
archaeological sites, when it is there is often plenty of it. "You
find it in dry areas, in frozen places and in bogs," says Macko.

When Macko and Engel compared the chemistry of hair from modern
people and ancient mummies, they found that the amino acids in ancient
keratin survived in exactly the same proportions. They also bombarded
hair with radiation to mimic ageing. Still the amino acids remained
the same. And if these proportions don't change, then neither should
the proportions of stable isotopes. "The stability of collagen can be
suspect," says Macko. "But even in 5000-year-old hair, the amino acids
look the same as if it was cut from a living scalp today. So when you
do have hair, you know it's well-preserved."

Hair is remarkably resilient. Age does not change it, nor do modern
hair treatments or natural dyes of the sort ancient people might have
used. O'Connell's experiments with shampoos showed that they make no
difference to the results. "You can compare modern and ancient hair
without worrying about modern treatments," she says. Dyes don't seem
to have any effect on the result either. "I tried henna - a beauty
treatment for thousands of years - and that didn't make any
difference," she says. Nor does it matter if the hair is brown or grey
- or which part of the body it comes from.

Hair on ancient corpses might have been treated in other ways. The
ancient Egyptian embalmers speeded the drying of bodies with natron
(sodium carbonate), a salt gathered from saltpans and lakes. And
sometimes they anointed hair with palm oil. Neither changes the
chemistry of the hair, says Macko. "Almost nothing we do changes its
composition. This makes hair the ideal artefact to address questions
of diet."

So far, Macko and Engel have analysed hair from two very different
groups of Egyptian mummies: ancient aristocrats who lived around 4000
years ago, and Christian Copts from around the 8th century. From the
Americas, they have analysed some of the famous Chinchorro mummies
from Chile, which are between 800 and 5000 years old. They also
analysed hair from Otzi, the Neolithic man who died on a high Alpine
pass 5300 years ago.

Where possible, Macko analyses the remains of food from the same
archaeological sites, so he can compare hair signatures directly with
the foods people were eating rather than modern foods. This way, he
doesn't have to worry about the influence of artificial nitrogen
fertilisers, or the shift in carbon signals as a result of burning
fossil fuels. Food remains from the Chinchorro sites include corn, a
tuber called jiquina, the remains of shellfish and sea-lion bones. In
the case of the Copts, Macko had samples of many local plants,
including cow beans, wheat, and seeds from grapes, dates and
watermelons.

The hair from Egypt revealed that these two peoples-separated by
thousands of years by race, religion and class - ate very different
diets. The Copts, whose bodies were mummified naturally in the desert
sands, represent a cross section of society: rich, poor and
middle-class. "There was a huge range of foods available - almost like
the supermarket diet," says Macko. "Some ate vegetables, some ate fish
and some ate meat." In fact, the Copts' eating habits were not unlike
those of today's undergraduates.

Exclusive eating

The older mummies from Egypt's Middle Kingdom period had a far more
restricted diet These were the Egyptian elite, wealthy enough to
afford the best embalmers. Hair from these aristocrats gave a very
uniform signal, suggesting that they all ate much the same, including
a significant amount of meat. "We don't know if this reflects what
they were allowed to eat or what they chose to eat," says Macko.

The Chinchorro mummies came from three burial sites in the Atacama
desert in northern Chile. The people buried at Morro, on the coast,
ate seafood and little else. Their isotope signatures suggest that
perhaps 95 per cent of their food came from the sea. At Maderas Enco,
5 kilometres inland, people ate a wider variety of food, but still
about half of it was seafood. The third site was in the Azapa valley,
around 30 kilometres from the sea. With one exception, these people
had been eating a mixture of C3 and C4 plants and a little meat,
perhaps llama, plus a small amount of seafood. The odd mummy out had
been eating almost nothing but seafood. Who was this person, who
clearly came from the coast but was buried high up in the desert?
"Maybe he was a travelling salesman, perhaps a fishmonger from the
coast," says Macko. Whoever he was, his hair shows that the
Chinchorros had dealings with people from quite distant settlements.
"This is evidence you couldn't have got any other way," says Macko.

And then there's Otzi the iceman. There is only one Otzi, so Macko
and his colleagues were lucky to have even a scrap of his hair. What
they found has raised a few eyebrows. The iceman's isotope signature
matches that of a modern vegan who eats mostly C3 plants. Opinions
vary on who Otzi was - perhaps a shepherd or a shaman or a hunter. But
he wore clothes made from skin and carried weapons designed for
hunting ("Blood on the axe", New Scientist, 12 September, p 40). The
wear on Otzi's teeth suggests a diet rich in grains and plant
material. But was he really a vegan?

Hair grows about a centimetre a month, so a change of diet, even for
a couple of months, can leave its mark. Otzi's isotope signature could
correspond to a time of plenty, with a good supply of grains, berries
and fruits. Hair that grew in the depths of winter might tell a
different story, with more reliance on dried meat to tide Otzi over
the winter.

The speed with which isotope signatures appear in hair makes it ideal
for teasing out information on changes in diet over the course of a
year or two-given a long enough strand of hair. By sampling at
intervals along it, researchers should be able to spot seasonal
variations, with a switch to a different source of food, or even a
regular rotation of crops. "Hair is fantastic if you have a suspicion
that people had a seasonal diet," says O'Connell.

Macko is now keen to look at samples of hair from a wider range of
ancient people, including the Bronze Age bog bodies of Denmark. Most
of these sacrificial victims have fine heads of hair but little bone,
which dissolved in the acid bog waters. Some of these bodies still
have the remains of their last meal in their stomachs. But as Macko
points out, a last meal can be very different from the everyday diet.
Hair from a collection of around two hundred mummies discovered
recently in the Peruvian rainforest could reveal much about the fives
of forest dwellers, whose diet consists mainly of forest fruits and
game.

But what Macko would really like is hair from people suspected of
eating their neighbours. "Cannibals should be a step higher up the
food chain from people with a more normal human diet," he says.
"They'd certainly be different from those on a grocery-store diet."

COOL! i wonder if being a veg who eats lots of algae would have a different reading than one who didn't. curious...

lacto-ovo vegetarians look like omnivores--interesting. as they say, milk is like liquid meat.

Amazing article!