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Genomics & Race |
Race Genes?
No. There are variations within our genes, but the overwhelming majority don’t occur along the lines we define as racial.
But scientists have discovered quite a bit about the biological markers
that point to our interconnectedness as human beings. In some cases,
cultural beliefs have been substantiated by information in DNA.
One Big Dysfunctional Family
All
of us human beings share 99.9% of the same DNA. This really makes sense
when you think about it. After all, normally we all have two arms, two
legs, a torso, the same internal organs, a head with a wonderful brain
cushioned inside, a skeleton and muscles to give us shape, skin to
cover us, sense organs to monitor our world(s), etc., etc., etc.
In light of genetic data that’s been uncovered in the last 20 years,
scientists speculate that we’re even all related to a single small
human population that hunted, gathered, argued, fought, bred and died
in Africa some 100,000-200,000 years ago.
And if that’s still too far in the distant past for you to find
relatives, Michael Hopkin, in a recent article in the UK’s prestigious Nature
magazine, points out that we human beings are even more closely related
than we ever imagined. He summarizes research done by Douglas Rohde and
colleagues at MIT indicating that everyone living today has a common
ancestor who lived a mere 3,500 years ago. No wonder we have trouble
getting along: we’re family!
And although humans have been (and probably will continue to
be) great migrating interbreeders, the main reason we share
so much DNA is that so much of it codes for ‘simply’
being human!
Of course, when you look at the TREMENDOUS visible physical variation
among individuals in your neighbourhood, your city, your country,
hemisphere and planet, you realize that this ‘leftover’ 0.1% contains
some pretty significant information! But there isn’t one gene that
makes you a particular race.
Again, there are variations within our genes – but they don’t occur
along lines that we define as racial.
We’re Genetically Divided in Fewer Ways than We Think
Today, race is considered to be a cultural construct, defined
more by language and custom than by biology. Nevertheless, there is
general agreement among population geneticists that there are five
groups (see below). It just isn’t always easy to fit people into them.
"Noah A. Rosenberg and Jonathan K
Pritchard, geneticists formerly in the laboratory of Marcus W. Feldman
of Stanford University, assayed approximately 375 polymorphisms called
short tandem repeats in more than 1,000 people from 52 different groups
in Africa, Asia, Europe and the Americas. By looking at varying
frequencies of these polymorphisms, they were able to distinguish five
different groups of people whose ancestors were typically isolated by
oceans, deserts or mountains: sub-Saharan Africans; Europeans and
Asians west of the Himalayas; East Asians; inhabitants of New Guinea
and Melanesia; and Native Americans. They were also able to identify
subgroups within each region that usually corresponded with each
member’s self-reported ethnicity.”
(Michael J. Bamshad and Steven E. Olson. Does Race Exist? Scientific American [November 10, 2003])
Geneticists use these kinds of classifications to approximate a
population history. And because social definitions of race are so
varied, it may surprise some people that geneticists identify so few
groups. People from Northern Europe, the Middle East, and India are all
considered Caucasians: culture and history divide us, not our genetics.
Common DNA and Common Culture
Genetic information can now be used to identify a common heritage among
members of a particular cultural group (Bamshad and Olson, 2003), even
when that cultural group includes a number of ‘races’. For example,
there have been very interesting studies done on male representatives
of the Cohanim (Cohen) priestly line in Jewish population groups all
over the world.
According to Biblical tradition, the Cohanim trace their line back
three thousand years to Moses’ brother Aaron. Dr. Karl Skorecki
hypothesized that all these Cohanim would share a common Y chromosome
if they are all truly descended from one man. It turns out that they do.
The clues lay in mutations in the non-coding regions (non
gene-containing regions) of the Cohanim’s DNA, specifically, of course,
on the Y chromosome.
Y chromosomes get passed from father to son, so they demonstrate a
patrilineal history. The non-coding regions of the Y chromosome don’t
undergo recombination
because its pair, the X chromosome, is sufficiently different.
Therefore, that non-coding region of the Y will stay stuck together.
Since the genetic information determining maleness occupies minimal
space, the Y chromosome is made up mostly of non-coding regions of DNA.
Now over long periods of time, mutations
tend to accumulate in these non-coding areas. (When mutations occur
within genes, disease or some other malfunction generally results which
tends to be selected out in the generations that follow.) Non-coding
regions can be a repository of ancient mutations. On the Y chromosome,
sections of these mutations can form a ‘genetic signature’ identifying
male descendents because information on the Y chromosome is passed
directly from father to son without going through recombination.
When Skorecki’s researchers analyzed particular markers on the Y
chromosomes of Ashkenasic and Sephardic Cohanim, they discovered that
“more than 95% of Ashkenasic and 87% of Sephardic Cohanim had the same
simplified haplotype.” (Hamer, 2004, page 189)
It’s important to point out that this ‘Cohanim sequence’ occurred in
Jewish people of many ‘racial’ types: red-haired people with blue eyes
and freckled skin, dark-skinned people with crinkly hair and brown eyes
and so on.
So in the case of the Cohanim, DNA evidence further legitimized a
tradition: only the biological son of a priest was allowed to function
as one. And because the Cohanim come from different races, their social
function within Judaism transcends the popular conception of race. The
multi-racial character of the Cohanim is a demonstration that stronger
elements than race unite people, and help turn us toward the more
genetically meaningful differences that ‘individualize’ them.
Populations and Individuals
“Approximately 93% of human genetic variation
occurs between two people in the same race - 85% between two people of
the same ethnic group and another 8% between ethnic groups within a
race. That leaves only 7% of variation between the major human races”.
(Lewontin, 1991)
When compared, racial group populations exhibit a very similar broad range of typical human variation:
“All populations have people who are taller and
shorter, fatter and thinner, braver and more timid, introverted and
extroverted, more decisive and more dithering. There is no continent of
uniformly brunette people to contrast with one of uniformly blond
people, or of uniformly tall people to contrast with one of uniformly
short people. The traits that differentiate Swedes and Kenyans at the
“racial” level are actually a very small proportion of the differences
detectable, which are distributed primarily among members of the same
population and between populations on the same continent.”
(Marks, 2003)
Even though certain diseases are more common in some groups, the same
mutations occur in other groups as well. Plus, we often quote a subset
of a race when discussing increased frequency of a disease. Cystic
Fibrosis, for example, is a common disorder among Northern Europeans,
with 1/25 people being carriers. It is thought that having one mutated
copy helped protect this group of people from cholera. (It is worth
getting CF in 1/2500 births because 1/25 people are better able to
survive cholera).
Mediterranean populations do not have an increased risk of CF but
do have increased incidence of thalassemia. Interestingly, thalassemia
is increased in Mediterranean and Africans populations where malaria is
present – two different “races”. Although both Northern European and
Mediterranean populations are Caucasian, the history of the populations
has shaped the frequency of genetic disorders.
Basically, there are differences across populations but they’re of
no appreciable value when you are identifying one person. A Chinese
woman may have smaller feet on average than the average Caucasian woman
but that doesn’t tell you what size of shoes to get her - or what kind
of shoes she likes.
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