I was talking with the genetics intern on my inpatient pediatrics team about random things in evolutionary medicine, and come to find out, every autosomal recessive condition has a heterozygous advantage… and they usually make a lot of sense.
Most biology students are familiar with the advantage of having sickle cell trait (one of the two alleles is mutated) in preventing malaria. But how about another recessive condition like cystic fibrosis (CF)? Back in the day, bouts of diarrhea could wipe out large fractions of a population because of drastic volume loss; however, being a heterozygote for CF meant that your symptoms would be significantly less severe. Less profuse diarrhea -> less water loss -> higher chance of survival. In a sense, carriers of the CF mutation were “selected” for.
Daily events like yawning can also be tied to an evolutionary advantage. The layperson would say yawning is indicative of boredom. Others claim that it provides us with a burst of oxygen by expanding our lungs. In reality, yawning opens up our eustachian tubes allowing pressure equalization across our tympanic membranes. This increases auditory acuity and sensitizes us to our surroundings. This is especially prevalent just before going to sleep, and we’re more vulnerable to “predators” (think cavemen days).
Of even more interest is when we see others yawn, many of us follow in suit. Why? Because if a member of your “pack” is yawning, they’re more likely to pick up danger nearby. If you want to survive, you should be doing the same – hence, the mirror yawn.
…maybe I’m the only one that finds these pearls to be incredibly awesome. I’ll definitely be reading more about evolutionary medicine this summer. 😀