Concept explainers
Between 70% and 85% of people will experience lower back pain at some point in life, and for many people, the condition is chronic. This state of affairs is an unfortunately painful consequence of the evolutionary process. We walk upright on two legs, but our distant ancestors walked on all fours. Thus, natural selection formed our vertically oriented spine by remodeling one whose normal orientation was parallel to the ground. Our spinal anatomy evolved some modifications in response to its new posture, but as is often the case with evolution, the changes involved some trade-offs. The arrangements of bone and muscle that permit our smooth, bipedal gait also generate vertical compression of the spine, and the resulting pressure can, and frequently does, cause painful damage to muscle and nerve tissues.
Why Backaches Are So Common?
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Biology: Life on Earth with Physiology (11th Edition)
- Some human traits may have arisen by sexual selection. Over thousands of years, women attracted to charming, witty men perhaps prompted the development of human intellect beyond what was necessary for mere survival. Men attracted to women with juvenile features may have shifted the species as a whole to be less hairy and softer featured than any of our simian relatives. Can you think of a way to test this hypothesis?arrow_forwardSome people think that many of our uniquely human traits arose by sexual selection. Over thousands of years, women attracted to charming, witty men perhaps prompted the development of human intellect beyond what was necessary for mere survival. Men attracted to women with juvenile features may have shifted the species as a whole to be less hairy and softer featured than any of our simian relatives. Can you think of a way to test these hypotheses?arrow_forwardWe have discussed the role of meat consumption in hominin evolution as an important source of fuel for our larger and metabolically costly brains. Do you think this hypothesis for why we have such large brains has merit? Why or why not? Can you think of any alternative hypotheses to explain the trend toward larger brain size over the past 2.5 mya?arrow_forward
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