From: Keith Henson (hkhenson@rogers.com)
Date: Fri 08 Aug 2003 - 13:56:15 GMT
At 09:04 AM 08/08/03 +0100, Derek wrote:
> --- Keith Henson <hkhenson@rogers.com> wrote: > At
>01:02 AM 06/08/03 -0400, Scott wrote:
> > Genes for
> > accumulating fat were advantageous when food
> > commonly was in short
> > supply part of the year. A change in the
> > environment to constant food
> > availability and these genes become a major
> > liability.
>
>Why? As long as they don't kill you before the end of
>your reproductive period, or stop you breeding during
>it, there is no genetic disadvantage whatsoever. This
>is also why natural seletion has not removed our
>susceptibility to cancers occurring in middle age and
>later.
I would have thought so too, but it seems that the effects happen early
enough in life to cause a major shift in genotype with respect to genes
contributing to diabetes. Perhaps it kills pregnant women without treatment.
I read this in the June 5 Nature when it was the free feature of the
week. Now you have to have a subscription to get it. The full article
discusses extremely rapid shift in the one population today where the
incidence is rapidly falling over a very few generations.
Keith Henson
http://www.weightlossresource.com/library/showarticle.cfm/ID/1289/T/health/cat/research/
UCLA Study Finds Clues to Diabetes Puzzle
WeightLossResource.com
06-05-2003
A diabetes epidemic that appears to have claimed the life of composer
Johann Sebastian Bach may explain baffling disparities in the disease's
rates among 21st-century ethnic groups, a UCLA geographer and evolutionary
biologist says in the current issue of Nature.
Aside from speculating that many people may carry genes that predispose
them to diabetes, researchers have been at loss to explain why, for
instance, only 2 percent of Europeans contract the disease as opposed to 13
percent of African Americans, 17 percent of U.S. Latinos and up to 50
percent of Native Americans.
"Immediately following Europe's last widespread famines centuries ago, a
diabetes epidemic appears to have killed a large number of Europeans with
these genes before they could be passed on to successive generations," said
Jared Diamond, a UCLA professor of geography and environmental heath
sciences. "Meanwhile, traditionally poor or rural non-European populations
have not experienced a diabetes epidemic -- until lately. So these people
still carry the genes in large measure, and as a result they become highly
prone to diabetes when they move into urban or Westernized settings, where
the disease's risk factors are more common."
If accurate, Diamond's theory means today's soaring diabetes rates will
continue to mount as people whose ancestors were never exposed to the
epidemic adopt the disease's twin risk factors: abundant food and more
sedentary lifestyles. Already, the disease affects 150 million worldwide.
"At its present rate of increase, within a few decades diabetes will become
one of the world's commonest diseases and biggest public health problems
with an estimated minimum of half-a-billion cases," Diamond writes in the
June 5 Nature article.
The findings relate only to type II -- or so-called adult-onset --
diabetes, a form of resistance to insulin, the human hormone responsible
for controlling blood sugar. When left unchecked, elevated levels of blood
sugar can result in the loss of limbs, vision or life, as well as an
increased risk of cardiovascular disease. Adult-onset diabetes often can be
controlled through dietary changes and exercise.
Diamond, the Pulitzer Prize–winning author of "Guns, Germs and Steel: The
Fates of Human Societies" (W.W. Norton, 1997) and winner of the National
Medal of Science, researched current and historic type II diabetes rates
among nine different population groups in 24 regions. He then examined the
groups' food history, including improvements in farming, Westernization or
urbanization.
He found that diabetes rates have risen in lock step with living standards
for the populations now most prone to the disease, including Arizona's Pima
Indians, U.S. Latinos, Pacific Islanders, Westernized Australian
Aborigines, African Americans, and urban Asians and eastern Indians. When
Yemenite Jews were airlifted to Israel from starving conditions several
decades ago, their diabetes rates jumped from 4 percent to 13 percent. When
New Guineans moved from a rural to urban setting, their diabetes rate shot
from zero to 37 percent, he found.
"Diabetes is a disease of increasing affluence," he said. "People eat more
and risk developing diabetic symptoms when they have more money."
Diamond's findings are consistent with a long-standing theory of an
evolutionary advantage to insulin resistance, which would tend to favor
populations with so-called "thrifty genes" that promote metabolism and
storage of blood sugars, thus allowing their carriers to better survive
periodic famines.
"Much like the gene that protects against malaria but also predisposes so
many people of African ancestry to sickle-cell anemia, the 'thrifty gene'
is a double-edged sword that becomes a liability only after living
standards improve," Diamond said. "Until a stable food source is secured,
the gene helps people survive famines, but afterward it puts them at risk
for the dangers of diabetes."
Europe was as prone through the Middle Ages and Renaissance to periodic
famines as any place, Diamond points out. European countries just happened
to develop stable food sources earlier than other parts of the globe. He
contends that a diabetes epidemic swept through Europe following the
region's last famines, beginning in the late 1600s.
"Europe's new reliability of adequate food supplies eliminated most
European diabetes-prone bearers of the thrifty gene," Diamond said.
Groups with the highest diabetes rates today, meanwhile, were until fairly
recently at periodic risk for starvation, so natural selection favored
those who retained the "thrifty gene." These groups often experienced an
"extra bout" of natural selection when an especially brutal famine in
historic times further concentrated the gene's carriers in the population,
Diamond found.
For instance, Arizona's Pima Indians experienced crop failures, widespread
starvation, and the likely enrichment of the surviving population with
thrifty genes after white settlers blocked access in the late 19th century
to a traditional source of irrigation water. With 50 percent of the tribe
now diagnosed as diabetic, the Pimas today lay claim to the world's highest
diabetes rates.
Diamond's theory would also explain another disparity in diabetes rates
that have puzzled researchers: why white Americans and Australians of
European extraction are three to four times more likely than Europeans
still living in Europe to be diagnosed with the disease.
"The Europeans who stayed at home tended to be richer that those who
emigrated, and the genotype that predisposed the stay-at-homes to diabetes
may already have been selected out by centuries of abundant food," Diamond
said. "Those who emigrated may have been the starvation-prone poor such as
the Irish who flocked to America during the Potato Famine of the 1840s.
These immigrants may carry the thrifty gene in larger proportion because
they did not enjoy the abundance in their homeland."
Bach's medical history is too poorly documented to pinpoint the cause of
his death with any certainty, but what is known of his last years is
consistent with an epidemic of type II diabetes that was sweeping Germany
at the time, Diamond found.
"The corpulence of his face and hands in the sole authenticated portrait of
him, the accounts of deteriorating vision in his later years and the
evident deterioration of his handwriting, possibly secondary to his failing
vision, are consistent with a diagnosis of type II diabetes," he said. "The
disease certainly occurred in Germany during Bach's lifetime, being known
as 'honigsusse Harnruhr' or honey-sweet urine disease."
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