Month: November 2010

Science online, Black Friday edition

Science online, Black Friday edition

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There may be more going on in those tiny heads than you think. Photo by shadarington.
  • Attention, bacon fans. Epileptic seizures can be controlled by an ultra-high-fat diet. (NY Times)
  • A few mg of prevention. Men who have sex with men can substantially reduce their risk of HIV infection by taking antiretroviral drugs. (NY Times, Dan Savage; original article in The New England Journal of Medicine)
  • Oh, now you tell us. Turkeys have enough social intelligence to recognize other turkeys from their own social group. (Jason Goldman for Scientific American)
  • Mmm. Cranberry genomics. Jason Goldman rounds up Thanksgiving-themed online science writing. (The Thoughtful Animal)
  • Meta-blogging science? The fellows behind Obesity Panacea have launched a blog about science blogging. (Science of Blogging)
  • A pithy comment is beyond the scope of the present linkfest. Incremental publication can be a good thing. (DrugMonkey)
  • Well, that was easy. A simple 15-minute writing assignment closes the “gender gap” between male and female physics students. (Not Exactly Rocket Science)
  • To be fair, science is pretty difficult. The leadership of the American Anthropological Association is moving to remove references to science from the organization’s mission statement. (Fetishes I Don’t Get)

And finally, Robert Krulwich narrates a beautifully animated short film about an enduring mystery of human behavior: our inability to walk in a straight line without help from visual cues.


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Is female orgasm adaptive? Let’s ask the clitoris.

Is female orgasm adaptive? Let’s ask the clitoris.

ResearchBlogging.orgWhether or not a trait is an adaptation, shaped by natural selection for a specific function, can be a surprisingly contentious question in evolutionary biology. When the trait in question belongs to human beings, though, “contentious” reaches a whole new level—because when evolutionary biologists consider humans, their conclusions get personal.
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Erotic sculpture on temple wall, Khajuraho, India. Photo by Abhishek Singh aka Bailoo.

Among the myriad traits and behaviors of Homo sapiens evolutionary biologists might choose to study, few can be as personal as the female orgasm. The adaptive function of male orgasm is about as clear-cut as possible—it’s a mechanistic necessity for uniting a sperm with an egg. But while female orgasm is enjoyable (or so I am told; this is as lousy a point as any to admit that my expertise in this phenomenon is purely academic), it isn’t necessary for fertilization. No man can be a father without having had at least one orgasm, but a woman could conceivably give birth to a huge family without having any.

To explain the existence of female orgasm in an evolutionary context, then, biologists have two options: (1) discover a way in which female orgasm shapes reproductive success indirectly, or (2) conclude that female orgasm isn’t an adaptation. Possibilities advanced for the first option range from the benefits of closer bonding with a mate—sex is, after all, about more than mere reproduction—to suppositions that the contractions associated with orgasm help draw semen into a woman’s reproductive tract.

The argument in support of non-adaptive female orgasm takes a developmental perspective: that female orgasm is really male orgasm, as experienced in a female developmental context. That is, women have orgasms for the same reason men have nipples—because the anatomies of both sexes are constrained by their origins in the same underlying developmental program. If this is the case, natural selection would work to optimize male orgasm, without necessarily affecting female orgasm—and that suggests a way to test whether female orgasm is an adaptation.

Natural selection removes less-fit versions of traits from a population—making that trait less variable within the population under selection. Traits that don’t affect survival or reproductive success, on the other hand, are free to accumulate variation via mutation. So non-adaptive traits can be identified by comparing their variation to traits with known adaptive functions.

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Who cares what natural selection thinks, anyway? Photo by JorgeMiente.es.

Psychologist Kim Wallen and philosopher of science Elisabeth Lloyd (who had advanced the hypothesis that female orgasm is non-adaptive in a 2005 book) made just such a comparison in a 2008 study. Variation in female orgasm would be challenging to measure, so they used the clitoris as an anatomic proxy. This let them use the penis—which shares a developmental origin with the clitoris and is presumably under natural selection associated with male sexual function—as an adaptive standard for comparison. In comparison to (flaccid) penis length, Wallen and Lloyd found that clitoris length was indeed more variable [$a]. As a second control, the authors also compared variation in clitoris and penis length to variation in the length of women’s vaginas, understanding that this trait, unlike the clitoris, is important for female reproductive success. Vaginal length turned out to be about as variable as penis length, and much less so than clitoris length.

There are several objections to be made to Wallen and Lloyd’s analysis, and many were made in a response [$a] by evolutionary biologist Vincent Lynch. Lynch objected to the use of length as the focal measure for the size of the clitoris, and showed that clitoral volume was about as variable as penile volume. (I would add that the study of social insects Wallen and Lloyd cite as a precedent for their analysis isn’t actually focused on variation, but on the symmetry of traits under consideration, which is not quite the same thing.) More critically, though, Lynch points out that there isn’t any known relationship between clitoral size and ability to achieve orgasm—so the data don’t have the bearing on the question that Wallen and Lloyd assigned in the first place. Lynch concluded that female orgasm is an adaptation after all—a more conservative interpretation of his result is that we can’t answer the question by measuring clitorises.

Understanding the evolution of human sexual behaviors can help us to figure out how best to navigate the tricky business of a sexual relationship with another person—an approach most recently exemplified in the book Sex at Dawn. But we also tend to view evidence that natural selection favors a particular trait or behavior as a kind of approval, or as evidence of what is “natural.” That’s silly. Whether or not they help to make more babies, orgasms are fun, and they’re a wonderful part of our most intimate expression of affection and love. In some respects, that’s all we need to know.

References

Crespi, B., & Vanderkist, B. (1997). Fluctuating asymmetry in vestigial and functional traits of a haplodiploid insect. Heredity, 79 (6), 624-30 DOI: 10.1038/hdy.1997.208

Lynch, V. (2008). Clitoral and penile size variability are not significantly different: lack of evidence for the byproduct theory of the female orgasm. Evolution & Development, 10 (4), 396-7 DOI: 10.1111/j.1525-142X.2008.00248.x

Wallen K, & Lloyd EA (2008). Clitoral variability compared with penile variability supports nonadaptation of female orgasm. Evolution & development, 10 (1), 1-2 DOI: 10.1111/j.1525-142X.2007.00207.x


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Science online, oily coral edition

Science online, oily coral edition

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Photo by ucumari.
  • Is anyone really surprised? Biologists working with NOAA have found the first clear evidence that the Gulf of Mexico oil spill is damaging coral reefs. (Deep Sea News)
  • Drink the corn liquor, let the Ritalin be. Could Ritalin help fight cocaine addiction? (Neurotic Physiology)
  • Trade-offs are a bitch. Adaptation for swimming and seal-hunting has made the polar bear’s skull structurally weaker than those of its closest relatives. (Not Exactly Rocket Science)
  • Admixture is fun! Razib Khan examines genetic studies of major human ethnic groups. (Gene Expression)
  • Gotta get funded to do the science. Over at dechronization, Rich Glor lays out tips on writing a doctoral dissertation improvement grant. (Part 1, Part 2, Part 3, Part 4 Part 5)
  • Scientific support for the siesta. A daytime nap can improve memory performance. (BrainBlogger)
  • Hint, hint. Submissions for the Open Lab 2010 collection of online science writing close at the end of the month. (The Thoughtful Animal)
  • This just in. Eating fewer calories than you burn results in weight loss—even when most of those calories are in Twinkies. (Weighty Matters)
  • Because you can’t develop Seasonal Affective Disorder if your brain is too small. Lemur species that live in habitats with greater seasonal changes have larger brains. (NeuroDojo)
  • Paging Dr. Pangloss. Psychologists are surprised to discover that the sight of cooked meat makes men less aggressive. They will no doubt also be surprised to find that it makes men ask for a fork and A-1 Sauce, too. (AOL News, McGill University press release)
  • Science is impossible. But that’s okay. Really. (We, Beasties)


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Science online, miracle cure edition

Science online, miracle cure edition

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Photo by rpongsaj.
  • Or, you know, the evolution of a super-cold. The discovery of a new way to stop viruses after they’ve already invaded cells could lead to an actual cure for the common cold. (The Independent)
  • Pleistocene Park, anyone? An extremely well-preserved mammoth skeleton unearthed near Denver, Colorado, may contain reasonably intact DNA. (The Denver Post)
  • Not just because of running to catch the bus. People who use public transit tend to be more active in general. (Obesity Panacea)
  • What the !?%$#**! do we know about human mutation rates, anyway? Less than you might think. (John Hawks Weblog)
  • This confirms what I already believe about both anti-vaxxers and corporate PowerPoint use. A GlaxoSmithKline presentation on the importance of vaccination leaves Jason Goldman pondering cognitive bias and the vital importance of good PowerPoint use. (The Thoughtful Animal)
  • All part of a conspiracy by socialist Radiolarians. Analysis of carbon isotopes in sediment cores suggest that a period of climatic warming in the middle Eocene was caused by increased atmospheric carbon dioxide. (Scientific American)
  • WTF is hepato-splen? That’s just one of many questions Scicurious can’t answer about a truly bizarre study investigating the effect of lunar phases on women’s menstrual cycles. (Neurotic Physiology)

Video this week, via io9: German researchers have determined that bats recognize bodies of water by echolocation because, when presented with a metal plate that reflects sound the way water does, they try to drink from it.


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