doctors began to remove inflamed appendixes in the late nineteenth century, mortality may have exceeded 20 percent. In other words, before the days of surgical removal, more than one person in a hundred died of appendicitis. That’s pretty strong natural selection.
Over the vast period of human evolution—more than 99 percent of it—there were no surgeons, and we lived with a ticking time bomb in our gut. When you weigh the tiny advantages of an appendix against its huge disadvantages, it’s clear that on the whole it is simply a bad thing to have. But apart from whether it’s good or bad, the appendix is still vestigial, for it no longer performs the function for which it evolved.
So why do we still have one? We don’t yet know the answer. It may in fact have been on its way out, but surgery has almost eliminated natural selection against people with appendixes. Another possibility is that selection simply can’t shrink the appendix any more without it becoming even more harmful: a smaller appendix may run an even higher risk of being blocked. That might be an evolutionary roadblock to its complete disappearance.
Our bodies teem with other remnants of primate ancestry. We have a vestigial tail: the coccyx, or the triangular end of our spine that’s made of several fused vertebrae hanging below our pelvis. It’s what remains of the long, useful tail of our ancestors (figure 14). It still has a function (some useful muscles attach to it), but remember that its vestigiality is diagnosed not by its usefulness but because it no longer has the function for which it originally evolved. Tellingly, some humans have a rudimentary tail muscle (the “extensor coccygis”), identical to the one that moves the tails of monkeys and other mammals. It still attaches to our coccyx, but since the bones can’t move, the muscle is useless. You may have one and not even know it.
Other vestigial muscles become apparent in winter, or at horror movies. These are the arrector pili, the tiny muscles that attach to the base of each body hair. When they contract, the hairs stand up, giving us “goose bumps”—so called because of their resemblance to the skin of a plucked goose. Goose bumps and the muscles that make them serve no useful function, at least in humans. In other mammals, however, they raise the fur for insulation when it’s cold, and cause the animal to look larger when it’s making or receiving threats. Think of a cat, whose fur bushes out when it’s cold or angry. Our vestigial goose bumps are produced by exactly the same stimuli—cold or a rush of adrenaline.
And here’s a final example: if you can wiggle your ears, you’re demonstrating evolution. We have three muscles under our scalp that attach to our ears. In most individuals they’re useless, but some people can use them to wiggle their ears. (I am one of the lucky ones, and every year demonstrate this prowess to my evolution class, much to the students’ amusement.) These are the same muscles used by other animals, like cats and horses, to move their ears around, helping them localize sounds. In those species, moving the ears helps them detect predators, locate their young, and so on. But in humans the muscles are good only for entertainment. 16
FIGURE 14 . Vestigial and atavistic tails. Top left: in our relatives that have tails, such as the ruffed lemur (Varecia variegates), the tail (caudal) vertebrae are unfused (the first four are labeled C1-C4). But in the human “tail,” or coccyx (top right), the caudal vertebrae are fused to form a vestigial structure. Bottom: atavistic tail of a three-month-old Israeli infant. X-ray of the tail (right) shows that the three caudal vertebrae are much larger and more well developed than normal, are not fused, and approach the size of the sacral vertebrae (S1-S5). The tail was later surgically removed.
To paraphrase the quote from the geneticist Theodosius Dobzhanslcy that begins this chapter, vestigial
Over the vast period of human evolution—more than 99 percent of it—there were no surgeons, and we lived with a ticking time bomb in our gut. When you weigh the tiny advantages of an appendix against its huge disadvantages, it’s clear that on the whole it is simply a bad thing to have. But apart from whether it’s good or bad, the appendix is still vestigial, for it no longer performs the function for which it evolved.
So why do we still have one? We don’t yet know the answer. It may in fact have been on its way out, but surgery has almost eliminated natural selection against people with appendixes. Another possibility is that selection simply can’t shrink the appendix any more without it becoming even more harmful: a smaller appendix may run an even higher risk of being blocked. That might be an evolutionary roadblock to its complete disappearance.
Our bodies teem with other remnants of primate ancestry. We have a vestigial tail: the coccyx, or the triangular end of our spine that’s made of several fused vertebrae hanging below our pelvis. It’s what remains of the long, useful tail of our ancestors (figure 14). It still has a function (some useful muscles attach to it), but remember that its vestigiality is diagnosed not by its usefulness but because it no longer has the function for which it originally evolved. Tellingly, some humans have a rudimentary tail muscle (the “extensor coccygis”), identical to the one that moves the tails of monkeys and other mammals. It still attaches to our coccyx, but since the bones can’t move, the muscle is useless. You may have one and not even know it.
Other vestigial muscles become apparent in winter, or at horror movies. These are the arrector pili, the tiny muscles that attach to the base of each body hair. When they contract, the hairs stand up, giving us “goose bumps”—so called because of their resemblance to the skin of a plucked goose. Goose bumps and the muscles that make them serve no useful function, at least in humans. In other mammals, however, they raise the fur for insulation when it’s cold, and cause the animal to look larger when it’s making or receiving threats. Think of a cat, whose fur bushes out when it’s cold or angry. Our vestigial goose bumps are produced by exactly the same stimuli—cold or a rush of adrenaline.
And here’s a final example: if you can wiggle your ears, you’re demonstrating evolution. We have three muscles under our scalp that attach to our ears. In most individuals they’re useless, but some people can use them to wiggle their ears. (I am one of the lucky ones, and every year demonstrate this prowess to my evolution class, much to the students’ amusement.) These are the same muscles used by other animals, like cats and horses, to move their ears around, helping them localize sounds. In those species, moving the ears helps them detect predators, locate their young, and so on. But in humans the muscles are good only for entertainment. 16
FIGURE 14 . Vestigial and atavistic tails. Top left: in our relatives that have tails, such as the ruffed lemur (Varecia variegates), the tail (caudal) vertebrae are unfused (the first four are labeled C1-C4). But in the human “tail,” or coccyx (top right), the caudal vertebrae are fused to form a vestigial structure. Bottom: atavistic tail of a three-month-old Israeli infant. X-ray of the tail (right) shows that the three caudal vertebrae are much larger and more well developed than normal, are not fused, and approach the size of the sacral vertebrae (S1-S5). The tail was later surgically removed.
To paraphrase the quote from the geneticist Theodosius Dobzhanslcy that begins this chapter, vestigial
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