Our ancestors
had brains - for dinner
Spread of disease-protection
genes points to cannibalistic
past.
11 April 2003
JOHN WHITFIELD
 |
| Funeral feasts used to put the Fore people at risk of contracting Kuru. |
| © Corbis |
|
|
Our ancestors may have eaten
each other's brains.
A new study has found genes
that offer protection from prion
diseases, such as
Creutzfeldt-Jakob Disease (CJD),
in populations on four
continents. This spread might be
an evolutionary response to the
dangers of cannibalism.
The safeguarding DNA is most
common among the Fore people of
Papua New Guinea. This is the
legacy of the Fore's custom of
eating their dead relatives in
funereal feasts. Last century,
cannibalism triggered an
epidemic of a deadly brain
disease called kuru.
"This is the signature of
natural selection in a
population where there's been a
devastating recent epidemic due
to cannibalism," says team
member Simon Mead of University
College London. Seeing the same
signature in other parts of the
world suggests that diseases may
once have spread by the same
route, he says.
Kuru and CJD are thought to
occur when misshapen prion
proteins warp other healthy
prions and clump together in the
brain.
About one in a million people
develop CJD spontaneously.
Others have caught it by eating
infected tissue, as seems to
have happened in the spread of
mad cow disease to cause variant
CJD in humans. It's thought that
the Fore caught kuru around the
turn of the twentieth century
from eating a sufferer of
spontaneous CJD.
The prion gene comes in
several types, and we have two
copies. People with two
different versions are less
likely to develop CJD or kuru,
and have a longer incubation
time when they do. People with
identical genes are more
vulnerable.
Nearly 80% of Fore women aged
over 50, who had participated in
funereal feasts, had the
protective gene, Mead's team
found1 - only women and children
ate their ancestors. Women born
after cannibalism was banned in
the mid-1950s were less likely
to carry the gene.
Mead's team also looked at
Africans, Asians and Europeans.
All carried some form of
protective mutation. "The genes
are more common than you'd
expect," says Mead. This
suggests that epidemics of prion
disease have struck throughout
history, he says.
Human bones bearing marks of
butchery are seen as evidence of
cannibalism among Neanderthals,
and among early modern humans
who lived in Spain 800,000 years
ago. Archaeologists have also
found faeces and cooking pots
from twelfth-century America
containing human muscle protein.
But evidence of cannibalism
in modern humans is scant, and
dates back only about 15,000
years, points out archaeologist
Nick Thorpe of King Alfred's
College in Winchester, UK.
"Most archaeologists and
anthropologists would accept
that there has been
cannibalism," says Thorpe. "But
it's much more difficult to know
how common it has been." He
suspects the practice has been
widespread but rare, appearing
and dying out many times.
The key thing to find out,
says Thorpe, is how common
cannibalism would need to be for
the genetic variant to arise.
Mead says that his study can't
answer this, nor the question of
when or where the protective
genes arose. "It has to have
been before recorded history,"
he says. |
