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• Category: Science 
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Go see it here: a blog carnival devoted to the best ecology and environmental science posts from across the blogosphere. This might be a nice complement to Tangled Bank…

• Category: Science 
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In an interesting paper published in the Jan, 2007 issue of Hormones and Behavior, researchers describe a phenomenon they claim is unique to human females; their overt display of fertilty. Specifically, around the time of maximum fertility, women show enhanced “self-grooming” behavior and dress in a more provacative manner in an apparent attempt to solicit copulations. Even more interesting, and in support of a claim I have made previously, is that even females in long term “monogamous” relationships exhibit these behaviors. (difficult to imagine how or why behaviors like this would evolve under the humans are monogamous hypothesis)

I’ll just remind people that while the idea of unconscious regulation of overt behavior that enhances host reproductive opportunities, there are even cooler stories where parasite infection effects sexual behavior similarly.

While this is an intersting study, one might ask the following additional questions:

  1. Does the magnitude of solicitation depend on the quality of either the existing mate or extra pair mate? If this is an adaptive behavior, you would predict that solicitation should increase as existing partner quality decreases or as extra-pair mate quality increases.
  2. Is there a difference in male perception of this solicitation when looking acoss male quality or relationship status?
  3. Does solicitation vary with MHC genes? (Do Women with rarer alleles solicit less?)
  4. How might one get a judge-jobs? “hot-woman photograph evaluator”

Any interest in replicating this here at GNXP? Women- submit randomly chosen photos to me or to Razib, one just after your period (low fertility), one about 2 weeks later (peak-fertility). We can assemble an “expert panel” of judges to evaluate …

Paper Abstract (and doi)

Humans differ from many other primates in the apparent absence of obvious advertisements of fertility within the ovulatory cycle. However, recent studies demonstrate increases in women’s sexual motivation near ovulation, raising the question of whether human ovulation could be marked by observable changes in overt behavior. Using a sample of 30 partnered women photographed at high and low fertility cycle phases, we show that readily-observable behaviors – self-grooming and ornamentation through attractive choice of dress – increase during the fertile phase of the ovulatory cycle. At above-chance levels, 42 judges selected photographs of women in their fertile (59.5%) rather than luteal phase (40.5%) as “trying to look more attractive.” Moreover, the closer women were to ovulation when photographed in the fertile window, the more frequently their fertile photograph was chosen. Although an emerging literature indicates a variety of changes in women across the cycle, the ornamentation effect is striking in both its magnitude and its status as an overt behavioral difference that can be easily observed by others. It may help explain the previously documented finding that men’s mate retention efforts increase as their partners approach ovulation.

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EDIT: I just found a paper (posted here)estimating the rate of human EPC to be between

• Category: Science 
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Scoop out their sperm!!!

I’m writing a series on human behavioral ecology over here, and am currently writing about sperm competition. Obviously, any strategy that enhances your likelihood of fertilization should be strongly favored by natural selection. In particular, I was thinking of probabilistic strategies that enhance the likelihood that your sperm does the job (as compared to rival males sperm). In insects, penile morphology has somewhat frequently evolved to incorporate a complex “sperm scooping” device.

On an aside, I note that the complex penile morphology (sperm scoopers) is conspicuously missing from Dembski’s list of “things-too-complex-to-have-evolved” without a designer.

Anyway, I found a paper that describes the human penis as a sperm displacement device (full text here).

Selected Excerpt: “…found that males appear to modify the use of their penis in ways that are consistent with the displacement hypothesis. Based on anonymous surveys of over 600 college students, many sexually active males and females reported deeper and more vigorous thrusting when in-pair sex occurred under conditions related to an increased likelihood of female infidelity.”

Man isn’t science fun…

Update from Razib: Sperm competition part n, sperm competition.

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A.K.A smelly t-shirt experiment revisited. These experiments basically ask women to evaluate the “sexiness” of a man’s body odor. Turns out, women consistently rated odors of men with dissimilar MHC genes to be most attractive. Here is a link to some background info. Similar studies have been done in mice and other primates and show that all else being equal, there is a preference for MHC dissimilarity. Just like in humans, the mechanism for the detection of genotype is olfaction.. Cool stuff.

In a bit of a twist, UNM researchers recently repeated the “sweaty t-shirt” experiment, but asked different questions. Instead of attractiveness, they were interested in looking at sexual receptivity and rate of extra-pair-matings. Results of their findings are here.

The take-home message.. If you’re partner doesn’t find your B.O., attractive, chances are, they’re likely to find someone else’s whose is…

• Category: Science 
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