Is evolution to blame for cancer, obesity, diabetes and cardiovascular disease?
Yesterday we covered a contentious report that higher IQ correlates to non-religious views. So it is telling that a recent Gallup poll found that 44% of Americans believe that God created human beings in their present form and many also think the human body is perfectly designed.
However, most scientists believe the modern human body as a collection of evolutionary compromises as our ancestors adapted to changing conditions, and that some of those changes created the seeds for our own disease issues. So many things have changed in our environment such as increased hygiene which could lead to our auto-immune systems weakening, a change in diet resulting in obesity, and a jaw foreshortening resulting in wisdom teeth overcrowding. Evolution is having a hard problem keeping up with the pace of environmental change and technological advancement
But many evolutionary advantages came with trade-offs. It’s long been known, for example, that gene variations that protect some Africans from malaria make them vulnerable to sickle-cell anemia. Genes that helped early Africans retain salt guarded against dehydration in tropical climates now put some African-Americans at risk for high blood pressure today.
And some body parts that provided a benefit at some time in human history pose challenges today—a phenomena Texas Tech University geneticist Lewis I. Held Jr. calls “bislagiatt,” an acronym for “but it seemed like a good idea at the time.”
Among the body’s bislagiatt parts Dr. Held catalogs in his book, “Quirks of Human Anatomy,” are men’s testicles that hang outside the body because sperm develop best at slightly cooler temperatures—but that makes them vulnerable to injury.
In women, the mismatch between mother’s narrow pelvis (which facilitates walking upright) and a newborn’s large head (which facilitates cognitive development) makes childbirth a painful and sometimes dangerous process.
The appendix, which scientists think served as a fermentation chamber for helpful intestinal bacteria in primates, is less needed now that people have varied diets and cook food.
The human mouth has also evolved unevenly. Teeth shrank considerably as agriculture changed our ancestors’ diets from mostly meat and plants to mostly carbohydrates. The human jaw shrank even faster, making wisdom teeth largely useless and creating the overcrowding that people face today.
Why haven’t years of evolution corrected these quirks? “Many features of our anatomy operate ‘under the radar’ of natural selection,” says Dr. Held. That is, they generally aren’t problematic enough to affect people’s survival before they reach reproductive age, so they keep getting passed on. Some experts think that wisdom teeth and the appendix may be slowly on their way out—some people are already born without them—since they do sometimes cause life-threatening infections.
These days, the key driver of evolutionary change isn’t who survives long enough to have children, but who has the most children and how soon they start.
