An emerging science shows that sickness is needed, and not all bad
For most scientists, believing in evolution means accepting that there’s a logical explanation for every little thing—every cell, every sneeze, every flash of pain or joy. And yet anyone who has ever come face-to-face with serious illness might reasonably ask, what higher purpose could disease possibly serve? In his new book Survival of the Sickest, neurogeneticist Sharon Moalem sets out to prove that disease is not only necessary, but it has been a surprisingly good friend to humankind over the years, helping to ensure our survival in the face of plagues, famines and radical climate changes.
Moalem, a 33-year-old Toronto native who now conducts research at New York’s Mount Sinai School of Medicine, stumbled upon the science of evolutionary biology as a precocious 15-year-old. At 18—already a regular patron of the medical library—he diagnosed himself with hemochromatosis (HHC), a rare hereditary blood disorder that interferes with the body’s ability to process iron. If left untreated, HHC causes excess iron to build up in the organs. Eventually, a person will literally rust to death. “People thought it was very rare, so when I went to see my physician, he laughed at me,” says Moalem. “Then he ran some tests and my iron was sky high. He thought there was something wrong with the machine.” Now Moalem donates blood every 90 days to keep his iron levels low.
Moalem’s doctor was right; the disorder is rare. But geneticists estimate that at least 30 per cent of people of western and northern European descent carry the gene. So several years ago, Moalem asked himself: if HHC is such a dangerous condition, why do so many healthy people still carry the blueprint? “In evolutionary terms,” he says, “that means we asked for it.” The answer, he later discovered, dates back more than 600 years and lies in the particular way people process iron. In an average person, iron is absorbed as needed by the body, and any excess simply passes through. In a person with HHC, excess iron is distributed throughout the body, with one key exception: it does not penetrate a type of white blood cell called a macrophage. “Macrophages,” says Moalem, “are the police wagons of the immune system.
They circle our systems looking for trouble; when they find it, they surround it, try to subdue it or kill it, and bring it back to the station in our lymph nodes.” The iron in an average person’s macrophages, he says, can sometimes be used by infectious agents, like those causing tuberculosis, to grow and multiply. But the irondeficient macrophages of an HHC carrier, researchers later discovered, are “the Bruce Lee of the immune system.”
In the 14th century, Europeans with the HHC gene, he concluded, would have been uniquely armed to ward off disease—most significantly, the bubonic plague.
Because so many survivors would have carried the gene, a large number of their offspring would inherit it, which may explain why no subsequent epidemic was ever as lethal as the Black Death of 1347-1350.
Survival of the Sickest reads like a Freakonomics for the medical set. Moalem shows how evolutionary medicine can explain all sorts of phenomena we can’t intuitively account for: why we need to urinate when we’re cold, why wearing sunglasses actually increases our risk of sunburn, and why people from certain parts of the world are more prone to diabetes, hypertension and alcoholism. In turn, these findings help researchers explore new, creative treatment options. Moalem has already conducted groundbreaking research at the University of Toronto that helped to establish a genetic link between HHC and Alzheimer’s. In 2005,
he published a theory suggesting that juvenile diabetes originated in northern Europe 12,000 years ago, brought on by a rapid drop in temperatures.
As a field of study, evolutionary medicine is only now gaining credibility in the wider medical community. “There’s finally a big move to get this into medical education,” says Moalem. “Doctors are not really exposed to basic evolutionary principles in school, so at first people dismiss it.” But as we move towards a system of customized health care,
from where and whom we descended will become crucial sources of information.
“Everything that we are, we’ve inherited from our ancestors,” says Moalem. “In our DNA, there’s a record of every plague and every environmental upheaval that our ancestors experienced. They’ve passed that down to us and it’s a great gift, but a complicated inheritance, too.” M
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