Is mixing races an intrinsically good thing, because
it reduces the number of relatives held in common? Professor Steve Jones,
probably Britain’s best known geneticist, apparently argues so, in an elegant
and witty Telegraph column:
Here are some illustrative paragraphs:
the malign effects of long, doubled-up DNA ……reflect the
extent to which large sections of the genome as a whole descend from a common
ancestor and, as a result, bring many damaged genes together in double copy.
They are unduly common in people with colon cancer, autism, Parkinson’s disease
and other conditions, and doctors have become very interested in scanning
patients to test their risk.
taking all
family ties into account, the person you sat next to on the bus this morning
is, on average, likely to be something like your sixth cousin, which means that
the two of you probably share at least one ancestor from the time of the Paris
Commune.
Finns (who
have a history separate from that of the rest of the continent) and Ashkenazi
Jews are even more likely to have close family ties; while in parts of
Pakistan, the average relationship of two random people is that of second
cousins, with their common ancestor alive at the time of the fall of France.”
in the
Western world incest (or at least inbreeding) is on the way out. The proportion
of people who identify themselves as of mixed race in Britain has almost
doubled in the past couple of decades, and one household in eight contains
members of different ethnic origins. For about half of the nation’s children with
an Afro-Caribbean parent, the other parent is white, so that on these islands
the pedigrees of two continents will soon merge.
Of course,
obstacles to sexual relations among groups have not disappeared. In the United
States, black-white unions make up only one in 60 new marriages today, far
fewer than in Britain – but even there the incidence has shot up from fewer
than one in 1,000 when Barack Obama’s parents tied the knot half a century ago.
A survey
of long-shared blocks of DNA in Americans of different age also shows how the
habit of sex with relatives is fading. Over the past century or so, the numbers
of doubled DNA sections have dropped by about a seventh, and their average
length by a quarter. All this reflects changes in patterns of mating – and the
increase in sex with strangers – since the invention of the motor car.
Comment: It would seem to be clear from this article that a
willingness to marry across “continents of origin” will reduce some of the
unpleasant effects of inbreeding. Put like that, some readers might consider
that such relationships are a public duty, diluting the deleterious effects of
quasi-incestuous parochial pairings. Even driving for 100 miles to find a
partner seems to convey a benefit.
Does this present a balanced picture? Well, it seems to suggest that relatedness
carries a clear disadvantage, with no countervailing advantages. Ashkenazi Jews
and Finns are lumped together with Pakistanis, without reference to
intellectual and scholastic abilities, or any behavioural differences. Let us consider the matter by way of some
simple comparisons.
The scientific and
cultural achievements of Ashkenazi Jews are legendary, and very well documented
(for example, Richard Lynn “The Chosen People: A study of Jewish Intelligence
and Achievement, Washington Summit Press, 2011). Sephardic Jews are a step
behind, but well above other contenders. Jews
have won 139 Nobel Prizes in science (Chemistry 33, Medicine 56, Physics 50).
The latter subject, in particular, would have been left in a very different
state without Albert Einstein, Neils Bohr, Wolfgang Pauli, Richard Feynman, and
Hans Bethe. (I have left out mention of
my old friend Joseph Rotblat, because despite being a physicist good enough to
work on the Manhattan Project, his Nobel Prize was for peace. Also, it allows
me to re-tell the Israeli joke about the 1978 Peace prize: “Have you heard that
Menachem Begin has won the Nobel Prize for Physics?” “For Physics? I thought it
was for Peace!” “No, no, no. His
qualifications in Physics were better”). Anyway, assuming an Ashkenazi Jewish
population of 10 million, that gives them 139
Nobels per 10 million or 107 per 10 million for all Jews. At a mundane and
worldly level, they tend to be prosperous.
Finns come third
in the world in the Programme for International Student Assessment 2009
rankings (behind Shanghai and Korea). They have got two Science Nobel prizes which
converts to 3.8 per 10 million. They tend to be prosperous.
Pakistanis do not
participate in PISA. One Pakistani has won a Nobel in Physics, the only Muslim
to have done so. Pakistan gets a per
capita score for science Nobels of 0.05 per 10 million. They tend to be poor.
I think you will
agree that these three populations differ considerably in their scholastic
achievements. They also differ in population size.
Ashkenazi Jews 10 million*
Finns 5.5 million;
Pakistanis 182 million
*There are roughly 13
million Jews world-wide, but far fewer in each nation state: Israel 6, United
States 5, Europe2 and Canada .4
This gives us a clue as to what is going on as
regards inbreeding. Whereas
the first two could be seen as being restricted by population size, that is not
the case for the 182 million Pakistanis, who should have no shortage of
potential partners. They should be free of inbreeding, so long as they can walk
several miles to the next village. The problem is that Pakistanis practice first cousin marriage. This is not a good idea. Europeans have usually
avoided it. The link below shows the global distribution of consanguinity.
The Pakistanis should
be able to free themselves from the risk of genetic disorders by avoiding their
first cousins. The Ashkenazis, on the other hand, who have already avoided
their first cousins, but mostly chose partners from among other Jews, have
decided to participate in genetic studies aimed at tracing the genes which
cause unpleasant neurological disorders, and taking steps to eliminate them,
probably by screening foetuses. They hope to avoid eliminating genes which lead
to high intelligence, though those cannot be identified at the moment (but are
being searched for by Prof Robert Plomin).
A more balance
presentation would be to say that some relatedness
is not bad of itself. The genetic code carries good and bad messages.
Restricted populations have an increased rate of genetic disorders. Cousin
marriages almost guarantee an even higher rate of genetic disorders, and those
are avoidable. It is misleading to consider
the genetic risks of relatedness without considering how it comes about, and
without looking at the benefits of positive characteristics in relatives.
Avoid first cousins,
but otherwise marry whom you choose, even among your own genetic group.
I take it that even first-cousin marriages aren't too bad, if indulged in only occasionally - it's doing it generation after generation that's the trouble, is it?
ReplyDeleteYes, the repetitions increase the risk.
ReplyDelete