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Human Sexual Selection

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  • Sexual Imprinting in Humans

    Apr 16th 2010

    By: Arielle

    2 comments

    Do you like your boyfriend because he looks like your father? This is the (somewhat disconcerting) question that we tackled in class this week. Similarity in mate partners, or homogamy, has been well documented in human sex partners. Choosing a mate with genetic similarity would mean that you would be more likely to share genes with your offspring. This week, we discussed an article that proposed that humans choose mates based partly on the mate’s similarity to their opposite-sex parent. The authors proposed that sexual imprinting occurs during childhood, leading humans to use their opposite-sex parent’s phenotype as a template for potential mates. In their study, the authors did find significant resemblances between fathers and their adoptive daughters’ husbands. This similarity diminished among daughters who reported receiving less emotional support from their fathers.

    The idea of sexual imprinting is very intriguing to me. Do I really unconsciously choose boyfriends because they look like my father? Although I am now re-examining all of my past relationships, I am not completely convinced by the authors’ argument. They claimed that the daughters chose similar looking husbands not because of phenotypic matching to self, but because of phenotypic matching to their fathers. However, couldn’t husbands also look like their father-in-laws simply because daughters look like fathers, and daughters choose mates that look like themselves (the self-matching theory)? As confusing as it is to follow all of these daughters-to-husbands-to-fathers strands, I guess my point is just that there seems to be many ways that the causality of these similarities could go, and I wouldn’t jump to the conclusion of sexual imprinting.

    If you’re interested, check out the article for yourself:

    Bereczkei, Tamas, Petra Gyuris, and Glenn E. Weisfeld. “Sexual Imprinting in Human Mate Choice”, Proceedings: Biological Sciences. Vol. 271, No. 1544

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  • Sexual dimorphism in primate brains

    Apr 12th 2010

    By: Katherine

    1 comment

    A couple of weeks ago, I shared Reinius and colleagues’ 2008 article, “An Evolutionarily Conserved Sexual Signature in the Primate Brain” with our group. The study compared gene expression in the occipital cortex of males and females from three primate species. The species were selected for their morphological sexual dimorphism: humans (Homo sapiens) and cynomolgus macaques (Macaca fascicularis) are sexually dimorphic, whereas common marmosets (Callithrix jacchus) are relatively sexually monomorphic. More than one hundred genes with sex-biased expression in the cortex were identified in humans and macaques, but less than ten such genes were identified in marmosets. Furthermore, 85 of the one hundred sex-biased genes were common to both humans and macaques. From these results, the authors posit that sexual gene expression dimorphism is, to an extent, conserved in primate cortexes.

    When I first found this paper, I was terribly excited since it used genetics to compare brain sexual dimorphism across species. Up until now we have focused primarily on human studies, which makes sense since we are a class about human sexual selection, but the “specialness” of humans can only be evaluated if we compare ourselves to other animals. Unfortunately, we had a rough time understanding the technicalities of the methods and statistical analysis, so we started speculating how the observed sexual dimorphism in brain gene expression would translate into behavioral dimorphism. From here the conversation quickly turned to the taboo subject of *gasp* the biological basis of behavioral sexual dimorphism in humans.

    Larry Summers resigned from his post as President of Harvard after he suggested that the underrepresentation of women in certain areas of academia was due to different aptitudes between men and women. No one can say that men and women think and act differently because of biology without being reproached, yet the general public is much more readily accepting of the biological basis of behavior in other animals. Granted, the notion of genetics influencing behavior is harder to wrap your head around than the idea of genes shaping morphology. This makes many people uncomfortable. Going back to Summers and the gender-gap in math/sciences…As a discussion group, we think that even though men and women, on average, probably do have different abilities at different subjects, one cannot judge an individual man/woman based on this difference (population statistics!), and the difference is a really small factor of gender disparity in the work place.

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  • Sex Lethal – Biology band

    Apr 1st 2010

    By: Max

    No comments

    A lighthearted take on the issues:

    Evolution Blues

    Like a Human Clone (Demo)

    Media

  • Very gradual change we can believe in

    Apr 1st 2010

    By: Max

    No comments

    This has caught fire on the interwebs. I think it’s pretty funny.

    Clever.

    Media

  • Sexual Dimorphism in Humans: Height

    Mar 25th 2010

    By: Avery

    No comments

    The fact that there is a sexual height dimorphism in humans–men are taller, on average, and women are shorter–is widely accepted.  This is probably the least controversial dimorphism that exists and thus possibly, then, good and broadly acceptable evidence for (at least past) sexual selection pressures in human evolution.  For these reasons, we read a few articles about human height dimorphisms for our meeting last week.  We ended up focusing on physical reproductive pressures that could lead to this dimorphism–this was the specific pressure that came up in analysis on what specific pressure causes this trend.  We recommend finding the articles listed below if you’re interested in this topic!

    Some problems we had with the studies were:
    1. we didn’t have the math background to judge the findings
    2. we wished we had access to the actual data sets

    Informal Bibliography for this discussion:
    “Human fertility variation, size-related obstetrical performance and the evolution of sexual stature dimorphism” by J.-F. Guegan, A.T. Teriokhin and F. Thomas (2000)
    “Women’s height, reproductive success and the evolution of sexual dimorphism in modern humans” by Daniel Nettle (2002)

    Sexual Dimorphism

    height, sexual dimorphism

  • About Us

    Feb 28th 2010

    By: Avery

    No comments

    This is a kind of “mission statement” for this website.  It will become a permanent page once we resolve our technical issues.

    Welcome! The purpose of this blog is to explore the effects of sexual selection on human evolution and on the behavior of modern humans.  We, the Swarthmore students studying this subject in a Directed Reading, feel that the current discussion on this topic comes from two opposing camps: either sexual selection theory is completely useless with respect to humans and everything it explains should be explained by social science and that the effects attributed to sexual selection in humans are written in stone and unquestionable.  We hope this blog will open up discussion between these two perspectives; we want to see what sexual selection theory can tell us about everyday life.

    We don’t claim to have the answers to many of the questions that arise in this kind of discussion, but we do have thoughts and resources we want to share.  We encourage readers to criticize, to applaud, to react in whatever way seems appropriate.  We want you to engage us in conversation.

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