Considering how long our species has been roaming the Earth, one would expect our bodies to be well adapted to the environment. Unfortunately, most of us still come with flaws– allergies, defects, and the like. Biologists would tell us that there is still more room for improvement, as humanity will continue to evolve in response to pressures in the environment. In Alex Bezzerides’Evolution Gone Wrong: The Curious Reasons Why Our Bodies Work (or Don’t), he tries to explain why we still experience defects regardless of our long history with evolution:
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Our eyes evolved originally in the ocean, where ancestral vertebrates dwelled and needed to see underwater. Around 375 million years ago, when they ventured to land, their eyes were already 100 million years old. Gradually, eyes in this lineage became land-adapted, but these organs have retained fluids and, as a result, never achieved the type of light refraction that would result in consistent sharpness of image on land. Light travels more slowly through water than it does through air, but to our advantage in modern times, even more slowly through glass. “Many of us take advantage of this fact by placing glass in front of our eyes to compensate for the imperfect job our corneas and lenses do in bending the light.”
Bezzerides offers nifty evolutionary explanations too for why we can distinguish more shades of green than any other color, and why our night vision is poor. He clarifies that it’s not only our evolution that makes for vision troubles today, but also our current behavior. Most of us spend way too much time in spaces that lack natural light. “Children who spend greater chunks of their day outside have a lesser risk of developing myopia than children who spend their days inside,” he writes. Kids don’t even have to be doing healthy things out there, it turns out, because it’s the light and not the activity that makes the difference.
Back trouble, the leading cause of disability globally, is directly traceable to primates’ leaving the trees for open areas more than 4 million years ago, Bezzerides notes. The move to the forest floor was “a pressure cooker” that caused human ancestors’ center of gravity to shift. For the first time, a primate could balance on only two feet; the human spine is shaped quite differently from that of our ape cousins’, with curves that cause a “precarious” structure. For example, “The inward, or lordotic, lumbar curve needs to be far enough inward to place the position of the spine under the head and to get the center of gravity above the hips,” Bezzerides writes. Back pain, and even intervertebral disc pain, happens all too readily with slight misalignments.
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