A New Way of Looking at Disease
By Jo Lynn Orr
The next time you reach into the medicine cabinet for some instant relief, you might want to take a moment to reconsider the long-term consequences. “When we get sick, our first inclination is to take a pill to make the symptoms go away, but that might not be the healthiest thing to do,” says UAB biologist David Kraus, Ph.D. Taking acetaminophen to reduce a fever, for example, tampers with “a highly coordinated set of physiological responses that allows our body temperature to rise in order to fight infection from foreign invaders like bacteria,” says Kraus. “If we reduce the fever, we are inhibiting finely tuned, evolved mechanisms that are useful for our health.”
These mechanisms are not restricted to fever—or disease, for that matter. The complex relationship between human health and evolutionary processes—generally studied under the name “evolutionary medicine”—has become a hot topic among scientists in a host of disciplines. Students are catching on, too. Kraus and fellow UAB biologist Jeannette Doeller, Ph.D., who are husband and wife, developed a popular course on evolutionary medicine in the Schools of Public Health and Natural Sciences and Mathematics that has seen enrollment soar from 25 students in 2003 to 150 last year.
Novel Approach to Disease
The appeal, Kraus explains, is that evolutionary medicine offers a novel way of examining issues of health and sickness. Unlike the prevailing model of modern medicine, it doesn’t focus on the immediate causes of disease, such as viruses and bacteria. Rather, it approaches human response to disease in terms of adaptation—the never-ending genetic changes our bodies make to survive in a hostile environment, and the changes that environment makes in response to us.
Jeannette Doeller and David Kraus
Humans are not the only species making adaptations, of course. And our actions often set up an evolutionary ripple effect that can have unwanted consequences, says Kraus. The current rise in antibiotic-resistant bacteria is a prime example. “By infusing so many antibiotics into our environment, we’re broadcasting a challenge to these organisms,” Kraus says. “Many of them will succumb to that challenge, but a few, through random mutation, will have the ability to break down those antibiotics and become resistant to them. So in essence, we’re paving the way for an entire population of new resistant microbes to come along.”
“It’s an arms race,” Doeller says. “And it’s a race that will never end,” notes Kraus. “It’s been ongoing since the beginning of biological organisms. Regardless of the type of organism, it will adapt to circumstances in order to reproduce its genes. Everything that enhances the reproductive outcome of the organism will be selected for.”
That being said, adaptations don’t always turn out to be beneficial in the short term. Kraus offers an example from personal experience. “When our first son was about four or five years old, I read an article in Scientific American by Randolph Nesse and George Williams, the authors of the book Why We Get Sick: The New Science of Darwinian Medicine,” Kraus recalls.
“One part that really caught my attention described the way our eyeballs form as young children—how they have to grow perfectly spherical in order to maintain an image that focuses on the retina. If we put small print or objects continually close to our eyeballs as they are growing, that stimulates the cells in the eyeball to elongate, creating myopia. As I was reading about this, I happened to glance at my son, who was drawing a picture with his face six inches from the paper, and I thought, this isn’t a good idea. Sure enough, within a year, he needed glasses.
Illustrations by Ernie Eldredge
“Evolution can’t make perfection—all it can do is create change by helping the organism and its components adapt to a new environment,” Kraus continues. “If we now put small print in front of the human eyeball—and we humans didn’t see print for 190,000 years of Homo sapiens history—we will increase the probability that the growing eyeball becomes malformed.”
Thanks to an abundance of fine print on paper and computer screens, myopia today affects 30 percent of American population, says Kraus. “In some Asian countries, among graduating high-school seniors, as many as 80 to 90 percent have myopia.”
Evolution doesn’t just affect physiology, genetics, and immunology, however; it affects behavior as well. “It is a social issue,” Doeller says. “For example, why do we experience anxiety? If you think about the evolutionary benefit of being anxious in terms of responding to a fight-or-flight situation, it makes perfect sense that people will have that response.”
The current obesity epidemic, which is fueled by our love of high-salt, high-sugar, and high-fat foods, also could have evolutionary origins. “Our past diet selected for these tastes: salt, sugar, and fat,” Doeller says. For our ancestors, the more calories a food offered, the better—it increased the time they could survive before the next meal. “So naturally, our bodies selected for the tastes of these high-calorie foods”—such as meat and honey, for example—“which were rare,” says Doeller.
“But foods containing vitamins and fiber, which are so good for us, were readily available through the plants we ate daily. Our ancestors consumed thousands of calories of those good foods every day, so there was no selective force to develop taste buds for them.”
Kraus and Doeller say the take-away message they give their students derives from an essay by Theodosius Dobzhansky, a Russian-born scientist who was a 20th century pioneer in genetics research: “Nothing in biology makes sense, except in the light of evolution.”