4. Unsupported intestines
Once we stood upright, our intestines hung down instead of being cradled by our stomach muscles. In this new position, our innards were not as well supported as they had been in our quadrupedal ancestors. The guts sat atop a hodgepodge of internal parts, including, in men, the cavities in the body wall through which the scrotum and its nerves descend during the first year of life. Every so often, our intestines find their way through these holes—in the way that noodles sneak out of a sieve—forming an inguinal hernia.
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