Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live by Marlene Zuk Page A
Authors: Marlene Zuk
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before we had the answer.
The crickets, it turned out, weren’t silent because they could have called but chose not to; they were silent because they lacked the apparatus to produce any sound at all. In the space of fewer than five years, or about twenty generations (taking a conservative estimate that the mutation appeared a few years before we noticed it, and with the crickets producing three to four generations per year), a new form of the cricket that we dubbed “flatwing” had become so common that we now estimate only about 10 percent of the crickets can still sing. (We just happened not to hear any on that first night, but later visits turned up a valiant handful of callers.) Additional research in my lab showed that the flatwings have a mutation in just one gene, but that single gene changes their wings so that they lack the equivalent of a fiddle and bow for making music.
Ordinarily, of course, not being able to call would be a tremendous liability for a male cricket, and if the mutation arose under normal circumstances, it’s virtually certain it would be an evolutionary dead end for its bearer, who would be unable to mate and hence unable to pass on any genes. But the flies change the rules of the game, and the flatwings are protected from detection by the lethal parasites by their silence, a veritable cloak of inaudibility that provides an enormous advantage.
This leaves one major question: How can a female cricket find her silent mate? The answer is turning out to be complicated, with the females apparently willing to mate with the silent males as long as the males are near one of the few remaining callers. But for our purposes, the point is that the crickets are an example of one of the fastest cases of evolution in the wild, taking not hundreds or thousands of generations, but a mere handful. In human terms, twenty generations is only a few centuries.
Although my crickets evolved more quickly than many species, they are by no means alone in changing during a relatively short period. Contrary to the commonly held notion that evolution is a ponderous process, requiring geological spans to produce any detectable change, scientists are now discovering that, as Andrew Hendry and Michael Kinnison note, “The fundamental conclusion that must be drawn is that evolution as hitherto considered ‘rapid’ may often be the norm and not the exception.” 1
The birds who came in from the cold
Perhaps because people are always interested in how fast events can happen, and also because people seem to have differing views on how long Earth and its inhabitants have been around, the rate of evolution has piqued our interest virtually since Darwin. One of the first to suggest a speed record for genetic change in a population, the most basic definition of evolution, was an extravagantly mustached scientist named Hermon Bumpus. Like the other residents of Providence, Rhode Island, at the end of the nineteenth century, Bumpus, an assistant professor of comparative zoology at Brown University, experienced some record-setting bad winter weather. But unlike most of them, he decided to profit from the misfortune of others in the name of science.
Somehow—his 1899 paper is mute about the source—the day after a particularly severe storm, Bumpus was brought 136 dead or stunned house sparrows. 2 I have searched in vain for the person or persons who thoughtfully provided Bumpus with his subjects, and their reason for doing so; was he well known for a general interest in dying birds? Did his friends and neighbors know that he had wanted all his life to record the miseries of house sparrows, those English invaders of North America? Was the purveyor of the bird bodies also interested in natural selection, only to be summarily dismissed from Bumpus’s subsequent work and denied a coauthorship? You don’t just cart around 136 sparrows in your pockets in the hope that they will come in handy sometime.
Alas, the backstory to this
The crickets, it turned out, weren’t silent because they could have called but chose not to; they were silent because they lacked the apparatus to produce any sound at all. In the space of fewer than five years, or about twenty generations (taking a conservative estimate that the mutation appeared a few years before we noticed it, and with the crickets producing three to four generations per year), a new form of the cricket that we dubbed “flatwing” had become so common that we now estimate only about 10 percent of the crickets can still sing. (We just happened not to hear any on that first night, but later visits turned up a valiant handful of callers.) Additional research in my lab showed that the flatwings have a mutation in just one gene, but that single gene changes their wings so that they lack the equivalent of a fiddle and bow for making music.
Ordinarily, of course, not being able to call would be a tremendous liability for a male cricket, and if the mutation arose under normal circumstances, it’s virtually certain it would be an evolutionary dead end for its bearer, who would be unable to mate and hence unable to pass on any genes. But the flies change the rules of the game, and the flatwings are protected from detection by the lethal parasites by their silence, a veritable cloak of inaudibility that provides an enormous advantage.
This leaves one major question: How can a female cricket find her silent mate? The answer is turning out to be complicated, with the females apparently willing to mate with the silent males as long as the males are near one of the few remaining callers. But for our purposes, the point is that the crickets are an example of one of the fastest cases of evolution in the wild, taking not hundreds or thousands of generations, but a mere handful. In human terms, twenty generations is only a few centuries.
Although my crickets evolved more quickly than many species, they are by no means alone in changing during a relatively short period. Contrary to the commonly held notion that evolution is a ponderous process, requiring geological spans to produce any detectable change, scientists are now discovering that, as Andrew Hendry and Michael Kinnison note, “The fundamental conclusion that must be drawn is that evolution as hitherto considered ‘rapid’ may often be the norm and not the exception.” 1
The birds who came in from the cold
Perhaps because people are always interested in how fast events can happen, and also because people seem to have differing views on how long Earth and its inhabitants have been around, the rate of evolution has piqued our interest virtually since Darwin. One of the first to suggest a speed record for genetic change in a population, the most basic definition of evolution, was an extravagantly mustached scientist named Hermon Bumpus. Like the other residents of Providence, Rhode Island, at the end of the nineteenth century, Bumpus, an assistant professor of comparative zoology at Brown University, experienced some record-setting bad winter weather. But unlike most of them, he decided to profit from the misfortune of others in the name of science.
Somehow—his 1899 paper is mute about the source—the day after a particularly severe storm, Bumpus was brought 136 dead or stunned house sparrows. 2 I have searched in vain for the person or persons who thoughtfully provided Bumpus with his subjects, and their reason for doing so; was he well known for a general interest in dying birds? Did his friends and neighbors know that he had wanted all his life to record the miseries of house sparrows, those English invaders of North America? Was the purveyor of the bird bodies also interested in natural selection, only to be summarily dismissed from Bumpus’s subsequent work and denied a coauthorship? You don’t just cart around 136 sparrows in your pockets in the hope that they will come in handy sometime.
Alas, the backstory to this
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