GENETICS
AND GENEALOGY
WE
ARE ALL AFRICANS
The
Times - November 17 2000
By Anjana Ahuna
Three
boys and their common Y chromosome inheritance - Alex Edmans,
left, and Bennet Summers, centre, share a common ancestor of
about 50,000 years ago with Amas Elturabi, right, of Sudanese
origin; this is shown by the M158 marker, which is in the blood
of all three.
The most
profound achievement of the last century can be summed up in
four letters: A, C, G and T. These letters- each the code for
a chemical - that make up the sentences that make up the chapters
that make up the book of human life.
The unique
string of three billion letters that results in each person
will spell out our individual's height, hair colour, and propensity
for diseases such as cancer and arthritis. But the letters will
also spell out something far more controversial - race. It is
genes that colour skin, that determine the texture of hair.
that shape the eyes, that sculpt the nose. This inevitable but
explosive spin-off of genetics has sparked a division among
those who cannot bear to close their eyes to the torrent of
valuable information flooding before them, and those who fear
a re-emergence of the concept of genetic superiority, which
underpinned the horrors of Nazi Germany. After all, if science
thinks it can extinguish or alter the genes that encode for
disease, why not the genes associated with specific groups of
people, such as the Ashkenazi Jews?
And if genes
underlie physical differences, why not mental differences, too?
The latter thesis still circulates among the fringe academics
- most notably among those who subscribe to the ideas outlined
in The Bell Curve, a 1994 book that implied black Americans
were not as smart as white Americans, and that Jewish Americans
and East Asians out-performed everybody else.
It is a
fact, however, that some genetic diseases are shockingly discriminatory
- cystic fibrosis, which can result in serious lung infections,
afflicts mainly whites, while sickle cell anaemia, a blood disorder,
predominantly affects blacks. Not to explore the genes involved,
scientists protest, is to leave ethnic groups in the grip of
disease for the sake of political correctness.
"We're
not in the business of designing smart bombs to wipe out races,"
says Dr Spencer Wells, a population geneticist at Oxford University
who has been studying the genes of different groups to trace
how modern man wandered out of Africa and settled other continents.
"People talk about the history of eugenics, and a lot of
the early research in this country was pretty suspicious, but
we are not doing this to divide people along racial lines. Our
species has a single, shared history, and we ought to learn
what it is."
The unfolding
drama that is the Human Genome Project tells us this so far:
99.9% of the DNA of every person on the planet is identical.
Roughly speaking, if you and your neighbour could compare your
genetic blueprints, written as As, Cs, Gs and Ts - adenine,
cytosine, guanine and thymine - the blueprints would be identical
apart from every thousandth letter. So the spectrum of human
variation - tall or short, black or white, blonde or auburn
- is squashed into a tiny fraction of the genome.
But what
we perceive as race does not make up the bulk of the 0.1% variation.
Wells says: "You can find more genetic differences between
two Africans than between an African and someone from the Outer
Hebrides."
This is
not an isolated example; the genetic variations within ethnic
groups are wider than those between different groups. The genes
of a pale Finn may match those of a dark South Indian more closely
than those of a blonde Swede. Wells has logged around 200 genetic
markers on the Y chromosome (for this reason the test can only
be done on males) that correlate with different areas of the
globe. Most people have multiple markers, suggesting migration
and mixing throughout human history. And, ultimately, we all
carry in our genes the traces of African ancestry. As professor
Chris Stringer, from the Natural History Museum in London, puts
it: "We are all Africans under the skin."
For that
reason, Wells says geneticists do not subscribe to the concept
of biology of race: "To me, race is a cultural construct.
I put it another way: there is a genetic variation among geographical
groups." He guesses that the characteristics we associate
with race, such as skin colour, account for no more than a tenth
of the variations between humans, which is 0.01% of our genetic
make-up.
The people
left Africa for other territories, they evolved different traits
to adapt to their new environments. The most obvious attribute
associated with race - colour - seems one of the most recent.
The variation in skin colour may date back only a couple of
thousand years, with paler skins emerging in colder regions
to allow more efficient production of vitamin D from sparse
sunlight. People living near the Equator evolved dark skins
to protect them from the sun's damaging rays. Interestingly,
the idea that pale pale skins reflect a more evolved race -
a tenet of white supremacy - is bogus, population genetics reveal.
It is most likely that when man appeared in Africa around 100,000
years ago, his skin was mid-brown. Paler and darker skins would
have surfaced in tandem, according to where people settled.
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