Why inflammation sometimes doesn’t resolve, and becomes chronic instead, is in some sense easily explained in evolutionary terms. “If I’m living 70,000 years ago at a time of food shortage,” says Ridker, “and there’s a drought, the 5 to 10 percent of people who will survive that drought are likely to have insulin resistance”—a tendency to store more calories as fat. “They’re going to live a little longer,” he continues. “When it finally rains, food comes, and that’s the survivor group. In a modern world of too much food, [insulin resistance] leads to diabetes. But in prehistory, it’s terribly important for survival.” While stored fat is beneficial during times of famine, it also harbors potentially damaging pro-inflammatory signaling molecules (see “Eating to Excess: Metabolic Inflammation,” below).
A second evolved factor is that prior to the development of antibiotics, disease “wiped out half the population before age five. So, people were under evolutionary pressure to have a hyperactive immune system.” Now, “most everybody survives childhood infections”….“But this hyperactive immune system remains, and adversely affects aging.”
“The third piece—beyond starvation and infection—is trauma,” Ridker says. “The saber-toothed tiger—or for women, bleeding to death during childbirth—selects on a genetic basis for hypercoagulable blood. So here we are, by definition all of us lucky enough to be alive today, with a consistent ancestry all the way back to the beginning. And we have all inherited a pro-inflammatory, insulin resistant, pro-coagulable state. Under the circumstances,” he continues, the fact that “we have an epidemic of diabetes and heart disease makes complete sense.” Evolutionary pressures have shaped a physiological system which is phenomenally well suited for surviving childhood infection, starvation, and predation. “But it contributes to many disorders of chronic aging…”