Theory not such a stretch
Evidence that the behaviour of our forebears can influence our genes has revived an old notion
Brad Evenson
National Post
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www.nationalpost.com]
Friday, November 01, 2002
Cheryl Purdey, The Edmonton Journal
Jean-Baptiste Lamarck, a 19th-century French biologist, was mocked when he proposed giraffes got their long necks from generations of stretching. He may have been right.
It may have been the giraffes that turned biologist Jean-Baptiste Lamarck into a standing joke in science. In 1809, the eccentric Frenchman wrote his theory that plants and animals can pass on characteristics they acquire in life to their offspring. He proposed that giraffes gained their lofty height by generations of stretching their necks, up and up to the juiciest leaves of the banyan tree. This stretching trait would then be passed on to the offspring. In contrast, failure to use an organ would cause it to wither and disappear, he wrote. This was how snakes lost their arms and legs.
By this evolutionary logic, men who pump weights would have muscular babies.
Even during his lifetime, Lamarck's ideas were cruelly mocked. He died blind and penniless, buried in a potter's field in Paris.
But in recent years, scientists have noticed something odd. There appears to be much more to heredity than plain old DNA. Now, a startling Swedish study may rehabilitate Lamarck's reputation.
The 15-year study, published this week in the European Journal of Human Genetics, suggests people who die of stroke, heart attack or diabetes may be suffering the lingering effects of their grandfather's overeating as a boy.
"You could say your ancestors ate you to death," says Gunnar Kaati, a professor of social medicine at the University of Umeå in Sweden.
Kaati, who refers to himself and his colleagues as "informed laymen" -- not professional geneticists -- launched the study in the late 1980s as a kind of resistance movement.
"We were dissatisfied with the conventional approaches to prevention of cardiovascular disease," he explains.
Conventional wisdom says exercising, and eating and drinking in moderation are the best ways to prevent cardiovascular disease. But the truth is these play a relatively minor role, reducing the risk of disease by as little as 15%, says Kaati.
So the University of Umeå researchers spent 15 years combing through Swedish archives to find out if traits acquired in life can influence heredity. Specifically, could eating a rich diet in childhood affect the fate of one's descendants?
The researchers selected four groups from remote Swedish villages, choosing at random 50% of the inhabitants born in 1890, 1905, 1920 and 1946. Then they compared the harvests of corn and potatoes in these villages, judging crops good or poor, to determine the degree of food availability.
"We have a certain advantage here in Sweden for these kinds of studies because we have pretty good data from almost the 16th century from church reports," says Kaati. "The priests were the authority that kept account of the people and you can find out ... what they died of, and we have transferred that to modern formats."
Their first finding, published in Acta Biotheoretica in 2001, was a bit vague. If boys born in 1905 had plenty of food as pre-teens, their grandchildren tended to die younger, the study found. If food was scarce, the grandchildren lived longer. The unexplained findings were shrugged off by mainstream biologists as a statistical quirk, error or coincidence.
But the current findings, which explore the lineage of 320 people born in 1890, 1905 and 1920, are considerably more specific. The researchers found the grandchildren of paternal grandfathers who had plenty of food during their pre-teen years died more often of cardiovascular disease or diabetes. (The researchers factored out death by accident, war and other non-medical causes.)
When the father or paternal grandmother lived through a famine during childhood, the children and grandchildren were protected from death by heart attack or stroke.
In the most striking finding, if the paternal grandfather enjoyed the bounty of rich harvests as a child, his grandchildren were four times more likely to die of diabetes.
"As far as we know this has never been shown before," says Kaati.
The finding suggests life experiences can alter the DNA we transmit to new generations. In this case, nourishment appears to alter the composition of sperm, since the inherited risk of disease was passed on most strongly by males.
History may judge Lamarck was simply ahead of his time.
He published Philosophie Zoologique, his grand theory of transmutation, a half century before the hybrid peas in Gregor Mendel's monastery garden began sprouting the modern theory of genetics. By the time Charles Darwin published his book On The Origin of Species in 1859, people who took Lamarck seriously were as rare as giraffes with short necks.
In classic Mendelian inheritance, offspring get a gene copy from each parent. If the gene for, say, brown hair is dominant, the offspring is a brunette. Darwin would say that if brown hair served as a camouflage against predators, then brunettes would prevail in the natural struggle for survival.
The problem is that heredity has a few inconvenient quirks.
Scientists say the subtle changes in DNA, known as "imprinting," can dictate when such disease genes will fire to life. Some are imprinted by the father, some by the mother. Consider two rare illnesses; Prader-Willi syndrome and Angelman syndrome. Both arise from mutations in a gene on chromosome 15. However, Angelman syndrome only appears when the DNA mutation is inherited from the mother. Prader-Willi only arises when the defective gene comes from the father. No one knows what causes imprinting.
The study of such DNA changes is called epigenetics.
Some scientists think epigenetics played a role following the Dutch famine of the Second World War. Pregnant women who starved during the famine, predictably, had small babies. However, these babies also gave birth to small babies, even though the postwar Netherlands had no food shortages.
In the debate of nature versus nurture, some have dubbed epigenetics "the nurture of nature." No one is certain how big a role it plays, but even studying it can invite ridicule.
"It has become difficult for people to think of heredity as involving non-genetic material," Steven Rose, a biologist at Britain's Open University in Milton Keynes told an interviewer. The research has continued, he says, but epigenetic research "remains semi-underground. You're not supposed to talk about it".
If epigenetics plays a big role, then the sequencing of the 30,000 genes in the human genome is only a rough start. Understanding the role of nature on the genome may assume huge importance.
In a commentary on the Swedish study, Marcus Pembrey, a British clinical geneticist at the Institute of Child Health at University College in London, says it is time to take epigenetic inheritance seriously. "Part of the reluctance to embrace the idea of epigenetic inheritance may be a mistrust of any hypothesis with a Lamarckian flavour," he writes.
Pembrey points out both Type 1 and 2 diabetes are associated with imprinted genes from the father. Is it possible, he asks, that some life event can alter a boy's testes between ages 8 and 11 as he begins to make sperm?
If having a plump childhood in rural Sweden could harm future grandchildren, imagine how the "rich harvest" of McDonalds fries and Supersize Cokes that has spawned an obesity epidemic in children will affect the unborn generations to come.
"If you speculate from our results," says Kaati, "it should be perhaps a bit scary to think about what could happen."
bevenson@nationalpost.com© Copyright 2002 National Post