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Romance, schmomance - Natural selection continues even after sex
February 13, 2007Some breaking news, just in time for Valentine's Day: Researchers have identified something called "sperm competition" that they think has evolved to ensure a genetic future. In sexual reproduction, natural selection is generally thought of as something that happens prior to - and in fact leads to — the Big Event. This thinking holds, for example, that we are drawn to physical features that tell us our partner is healthy and will give us a fighting chance to carry on our genetic lineage. But a new article in the February issue of Current Directions in Psychological Science suggests that the human male has evolved mechanisms to pass on his genes during post-copulation as well, a phenomenon dubbed "sperm competition."
In their article, Todd Shackelford and Aaron Goetz at Florida Atlantic University describe this as "the inevitable consequence of males competing for fertilizations."
How much more romantic can you get?
For a monogamous species, sperm competition may seem beside the point. But according to the authors, extra curricular copulations (i.e. affairs) appear to be a significant part of our ancestral history and could, evolutionarily speaking, spell disaster. A male whose female partner engages in some off-line dalliances unwittingly may be investing his resources - food, protection, credit rating — in a genetically unrelated offspring.
Competition may also affect sperm count, say the authors. The more time men spend away from their partners (time that their partners could have spent with other males), the number of sperm in their ejaculate increases upon their next copulation. In one study, the authors note, artificial phalluses constructed to resemble the structure and function of the human penis actually removed an ejaculate-like substance from an artificial vagina. This could indicate that the penis acts as an anatomical squeegee to remove an interloper's calling card.
But sperm competition is not just biology. According to the authors, many sexual behaviors such as deep copulatory thrusting may function to remove rival sperm. Sexual partners report that men thrust more deeply and quickly into the vagina following allegations of infidelity. The same periods of separation that increase sperm number in male ejaculates may also help to explain the increasingly lustful feelings human males develop after long periods of time apart from their mate. That is, the human male may want to copulate as soon as possible as insurance against possible extra-pair copulation.
These latest findings lead us to wonder about what other undiscovered ways humans have evolved in a world dictated by "survival of the fittest." In fact, the authors compare sexual adaptation to a Cold War phenomenon: "Sexual conflict between males and females," Shackelford and Goetz describe, "produces a coevolutionary arms race between the sexes," in which an advantage gained by one gender leads to counteradaptations in the other. They speculate that research may move beyond male adaptations to, for example, see if females have developed biological or behavioral mechanisms to increase retention of sperm from men with the most favorable genes. But that's for another Valentine's Day.
Association for Psychological Science
For a monogamous species, sperm competition may seem beside the point. But according to the authors, extra curricular copulations (i.e. affairs) appear to be a significant part of our ancestral history and could, evolutionarily speaking, spell disaster. A male whose female partner engages in some off-line dalliances unwittingly may be investing his resources - food, protection, credit rating — in a genetically unrelated offspring.
Competition may also affect sperm count, say the authors. The more time men spend away from their partners (time that their partners could have spent with other males), the number of sperm in their ejaculate increases upon their next copulation. In one study, the authors note, artificial phalluses constructed to resemble the structure and function of the human penis actually removed an ejaculate-like substance from an artificial vagina. This could indicate that the penis acts as an anatomical squeegee to remove an interloper's calling card.
But sperm competition is not just biology. According to the authors, many sexual behaviors such as deep copulatory thrusting may function to remove rival sperm. Sexual partners report that men thrust more deeply and quickly into the vagina following allegations of infidelity. The same periods of separation that increase sperm number in male ejaculates may also help to explain the increasingly lustful feelings human males develop after long periods of time apart from their mate. That is, the human male may want to copulate as soon as possible as insurance against possible extra-pair copulation.
These latest findings lead us to wonder about what other undiscovered ways humans have evolved in a world dictated by "survival of the fittest." In fact, the authors compare sexual adaptation to a Cold War phenomenon: "Sexual conflict between males and females," Shackelford and Goetz describe, "produces a coevolutionary arms race between the sexes," in which an advantage gained by one gender leads to counteradaptations in the other. They speculate that research may move beyond male adaptations to, for example, see if females have developed biological or behavioral mechanisms to increase retention of sperm from men with the most favorable genes. But that's for another Valentine's Day.
Association for Psychological Science
Natural Selection Current Events and Natural Selection News RSSFunny, you don't look related
When Charles Darwin visited the Falkland Islands during the voyage of the Beagle in 1835, he saw a wolf-like species, wrote about it in his diaries and correctly commented that it was being hunted in such large numbers that it would soon become extinct.
Can a plant be altruistic?
The concept of altruism has long been debated in philosophical circles, and more recently, evolutionary biologists have joined the debate.
Why nice guys usually get the girls
Female water striders often reject their most persistent and aggressive suitors and prefer the males who aren't so grabby, according to new research. Water striders are insects commonly seen skittering across the surface of streams.
Study sheds light on evolution of human complexity
A painstaking analysis of thousands of genes and the proteins they encode shows that human beings are biologically complex, at least in part, because of the way humans evolved to cope with redundancies arising from duplicate genes.
Inconspicuous leaf beetles reveal environment's role in formation of new species
Unnoticed by the nearby residents of St. Johnsbury, Vermont, tiny leaf beetles that flit among the maple and willow trees in the area have just provided some of the clearest evidence yet that environmental factors play a major role in the formation of new species.
Scientists discover largest orb-weaving spider
Researchers from the United States and Slovenia have discovered a new, giant Nephila species (golden orb weaver spider) from Africa and Madagascar and have published their findings in the Oct. 21 issue of the journal PLoS ONE.
Are humans still evolving? Absolutely, says a new analysis of a long-term survey of human health
Although advances in medical care have improved standards of living over time, humans aren't entirely sheltered from the forces of natural selection, a new study shows.
Fish vision discovery makes waves in natural selection
Emory University researchers have identified the first fish known to have switched from ultraviolet vision to violet vision, or the ability to see blue light. The discovery is also the first example of an animal deleting a molecule to change its visual spectrum.
Time in a bottle: Scientists watch evolution unfold
A 21-year Michigan State University experiment that distills the essence of evolution in laboratory flasks not only demonstrates natural selection at work, but could lead to biotechnology and medical research advances, researchers said.
New type of flying reptile discovered
An international group of researchers from the University of Leicester (UK), and the Geological Institute, Beijing (China) have identified a new type of flying reptile - providing the first clear evidence of an unusual and controversial type of evolution.
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