Schilthuizen published Natureâs Nether Regions , an exploration of what bug and beast sex can tell us about ourselves. It opens with one âunassailableâ fact, âsupported by millennia of bathroom graffitiâ: humans find genitals endlessly fascinating. Only recently, however, has this fascination been matched by scientific scrutiny.
Nether regions tend to be the most physically distinguishing feature of many species. Much more than a semen syringe, some penises are so elaborate that Schilthuizen compares them to an exploded grandfather clock. Despite centuries of studying the diversity of the animal kingdom, while biologists have catalogued these curious organs they have rarely questioned the reason for all that garnish.
When Charles Darwin penned his groundbreaking work The Descent of Man in 1871, he first described how competition for mates could drive changes in physical appearance and behaviour. Strong males pairing with âvigorous femalesâ would produce healthier offspring, he wrote, so allowing their particular traits to pass to future generations. Darwin, however, eschewed genitalia when discussing what an advantageous trait might be, preferring to assess colourful bird plumage and deer antlers.
Itâs unsurprising given the religious views of the day. âWe canât possibly have expected him to come out talking about genitalia,â says Leigh Simmons, a professor at the University of Western Australia. But, remarkably, it would take more than a century for scientists to seriously investigate these nuts and bolts.
In the 1970s, studies into damselflies found that females often mated with more than one male, but contrary to popular wisdom regarding playing âsecond fiddleâ, the succeeding male tended to father the offspring. Jonathan Waage, an entomologist then at Brown University, wanted to know how the second maleâs sperm usurped the first. He carefully sliced the female damselflies open, peering into the sperm mass left behind. Surprisingly, females had roughly the same amount of sperm if they had one or twomates. Where was half of the sperm going?
Waage noticed that when the second males had sex they spent more time âundulatingâ than releasing sperm. Indeed, these were conniving undulations â the flies were removing their rivalâs sperm. Close inspection of the damselfliesâ penises revealed they had handy tools to get this job done, including horns and a flexible head, which may âaid in scoopingâ, wrote Waage. The work, published in Science in 1979, was a breakthrough. It showed for the first time that genitals are not just vehicles to exchange DNA, but are at the heart of evolutionâs pressure.
According to Bob Wong of Monash University in Melbourne, before Waageâs work, scientists thought that reproduction was a âharmonious ventureâ between the sexes. âThen it dawned on us that sexual conflict is rife in the animal kingdom,â he says. In bed bugs, for example, males inseminate females by stabbing their penis basically anywhere in their partners. The ejaculate of some flies and butterflies contains toxic substances that manipulate females to fertilise more eggs, but it also shortens their life span.
Of course, females arenât taking all this lying down. Sexual conflict often creates an impressive arms race of genitalia, with the sexes trying to âone-upâ each other, says Wong. Male rove beetles, for example, have a long whip-like appendage that threads through the femaleâs genital tract to insert their sperm package directly. In response, the female has evolved an equally large vagina, ensuring only deft males can fertilise her.
Much of this sexual conflict arises because the reproductive needs of males and females rarely coincide in the animal kingdom. Males tend to want to spread their seed widely, while females are looking for quality. But why did this particular pattern
Nether regions tend to be the most physically distinguishing feature of many species. Much more than a semen syringe, some penises are so elaborate that Schilthuizen compares them to an exploded grandfather clock. Despite centuries of studying the diversity of the animal kingdom, while biologists have catalogued these curious organs they have rarely questioned the reason for all that garnish.
When Charles Darwin penned his groundbreaking work The Descent of Man in 1871, he first described how competition for mates could drive changes in physical appearance and behaviour. Strong males pairing with âvigorous femalesâ would produce healthier offspring, he wrote, so allowing their particular traits to pass to future generations. Darwin, however, eschewed genitalia when discussing what an advantageous trait might be, preferring to assess colourful bird plumage and deer antlers.
Itâs unsurprising given the religious views of the day. âWe canât possibly have expected him to come out talking about genitalia,â says Leigh Simmons, a professor at the University of Western Australia. But, remarkably, it would take more than a century for scientists to seriously investigate these nuts and bolts.
In the 1970s, studies into damselflies found that females often mated with more than one male, but contrary to popular wisdom regarding playing âsecond fiddleâ, the succeeding male tended to father the offspring. Jonathan Waage, an entomologist then at Brown University, wanted to know how the second maleâs sperm usurped the first. He carefully sliced the female damselflies open, peering into the sperm mass left behind. Surprisingly, females had roughly the same amount of sperm if they had one or twomates. Where was half of the sperm going?
Waage noticed that when the second males had sex they spent more time âundulatingâ than releasing sperm. Indeed, these were conniving undulations â the flies were removing their rivalâs sperm. Close inspection of the damselfliesâ penises revealed they had handy tools to get this job done, including horns and a flexible head, which may âaid in scoopingâ, wrote Waage. The work, published in Science in 1979, was a breakthrough. It showed for the first time that genitals are not just vehicles to exchange DNA, but are at the heart of evolutionâs pressure.
According to Bob Wong of Monash University in Melbourne, before Waageâs work, scientists thought that reproduction was a âharmonious ventureâ between the sexes. âThen it dawned on us that sexual conflict is rife in the animal kingdom,â he says. In bed bugs, for example, males inseminate females by stabbing their penis basically anywhere in their partners. The ejaculate of some flies and butterflies contains toxic substances that manipulate females to fertilise more eggs, but it also shortens their life span.
Of course, females arenât taking all this lying down. Sexual conflict often creates an impressive arms race of genitalia, with the sexes trying to âone-upâ each other, says Wong. Male rove beetles, for example, have a long whip-like appendage that threads through the femaleâs genital tract to insert their sperm package directly. In response, the female has evolved an equally large vagina, ensuring only deft males can fertilise her.
Much of this sexual conflict arises because the reproductive needs of males and females rarely coincide in the animal kingdom. Males tend to want to spread their seed widely, while females are looking for quality. But why did this particular pattern
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