Many of the chronic illnesses that have become the chief killers in industrialized societies result from traits that protected our ancestors, but that we now don't need so much, argues a physician in a new book.
, Goldman, dean of health sciences and medicine at Columbia University Medical Center in New York, writes in that our instinct to eat as much as we can, our ability to retain salt and water, and our blood coagulation system -- which promoted survival when people faced irregular food supplies and daily physical danger -- are now betraying us.
In the developed world, people are more likely to experience strokes and myocardial infarction than to suffer wounds that would cause them to bleed out, and they no longer need to pack on fat as insurance against famine, he notes. And early humans needed to be alert for constant lethal threats, but that hypervigilance in a world that is safer than at any other time in history can have the side effects of anxiety, phobia, and depression.
鶹ý asked Goldman about his book. He answered by email.
You take the really long view in Too Much of a Good Thing. Why do you think it's important for researchers and clinicians to understand that evolution and biology matter?
By understanding the way our ancestors slowly evolved to meet the challenges they faced over 10,000 generations, we can better understand how our bodies are built today. In Europe in about 1840, human life expectancy was 33 years, essentially unchanged from the best estimates for the Paleolithic era. In barely seven generations, life expectancy has increased about 2.5-fold as our brainpower has changed the world in which we live. However, our genes can't possibly change that fast, so our intrinsic human traits are still geared toward a pre-industrialized world in which the threats to health and survival were far different than they are today. As a result, we often find ourselves challenged by a genetic mismatch -- genes and traits that were critical for our ancestors' survival, but now are commonly more powerful than what we actually need today.
You write, "We're programmed to overeat whenever possible so we can store fat to protect against future shortages."
Couple this with the very modern abundance of available food and suddenly we have an obesity epidemic. But how does a good trait go so wrong?
For 10,000 generations, perhaps the biggest threat to human survival was starvation. We are the descendants of ancestors who managed to find and eat enough food and store the excess calories as fat -- so that they and their children could survive. Numerous genes stimulate our taste buds to like sugar and protein, encourage us to eat until we're full and sometimes even more, allow us to absorb essentially every calorie we eat, and efficiently store as fat any calories we don't immediately burn for energy. Furthermore, when we try to lose weight, regardless of how much we weigh, a series of hormones makes us hungrier and slows down our metabolism, so we tend to eat more calories even though we need fewer of them. All of these traits helped our ancestors survive food shortages and even famines, but they were not designed to help us in an era of plentiful food and especially calorie-dense and sugary treats -- all readily available in supermarkets to which we drive while expending minimal calories to obtain them. The industrial revolution and the subsequent scientific and medical advances have made life much safer and better, but one of the downsides is that we now can easily obtain and eat far more calories we need. And that is what is driving the modern epidemics of obesity, which affects about 38% of Americans, and diabetes, which afflicts about 10% to 14% of American adults.
Humans live much longer now they did during the hunter-gatherer stage. How much does the lengthened lifespan account for the health problems that you detail? Smoking might not be considered really bad, for example, if all humans died around age 60.
The longer we live, the more time we have for the traits that are now "too good" to cause problems. However, the fact that we already see an epidemic of childhood and adolescent obesity, with a resulting marked increase in the type of diabetes that we used to see only in adults, indicates that this problem is not exclusively a side effect of our increased longevity. And with this rise in obesity, as well as the marked increase in salt consumption, we're also seeing an increase in high blood pressure among adolescents and young adults. However, since obesity, diabetes, and even high blood pressure isn't likely to kill people before they live long enough to have children to perpetuate their genes, there is no reason to believe that "survival of the fittest" will eliminate the genetic mismatches that now account for about 40% of all deaths in America.
Is it easier to change biology rather than trying to change our environment through policies and incentives?
As I describe in Too Much of a Good Thing, I have some hope that regulation -- such as restrictions on the salt content of processed foods in parts of Europe and legislation regarding sugary beverages in Mexico -- can make a difference. However, Americans have generally been unenthusiastic about even very healthy regulations that are seen as limiting freedom of choice.
By comparison, voluntary behavioral changes, even with strong encouragement, have been very disappointing in terms of reducing caloric intake, reducing salt intake, or increasing exercise. In fact, it is because all three of these habits have generally gone in the wrong direction that 38% of Americans are obese, another one-third are overweight, and one-third have high blood pressure. Although behavior change would be wonderful and certainly is conceivable, it would seem imprudent to rely exclusively on a strategy that so far has been so unsuccessful.
Medications are extremely effective for treating high blood pressure and are by far the best way to reduce cholesterol levels and prevent future heart attacks. Newer medications and scientific advances hold great promise for being able to blunt the effects of genes we no longer need. I'm not at all sure that we will ever actually be editing everyone's genome, but by understanding our genes -- what they do, which ones we may no longer need -- we can find a variety of scientific approaches that can potentially alter their function to be more consistent with the modern environment our brains have created.