john hawks weblog

paleoanthropology, genetics and evolution

hormones

  • Testosterone, fatherhood,

    Fri, 2011-12-16 00:23 -- John Hawks

    Daniel Lende has done a nice interview with Northwestern University anthropologist Lee Gettler ("On Testosterone and Real Men: An Interview with Lee Gettler"). Gettler is a Ph.D. candidate in human biology and author of a recent paper that demonstrated a decline in testosterone levels in new fathers [1]. This paper got a lot of press attention and was a big topic of conversation at the recent AAA meetings. Lende takes the conversation deep into the science, and probes the relation of human biology to behavior.

    All of human behavior is mitigated physiologically- i.e. through the actions of neuronal pathways and neurotransmitters- so there’s really no way of divorcing biology and behavior, which are in constant “flux” and “conversation” with one another. One challenge for anthropologists and other scholars studying these domains is trying in some coherent way to disentangle “the chicken” and “the egg” in the transactional relationship between biology and behavior.

    I like the formulation, "All of human behavior is mitigated physiologically." See also my old post: "Allostasis in human evolution".

    References

    1. Gettler LT, McDade TW, Feranil AB, and Kuzawa CW. 2011. Longitudinal evidence that fatherhood decreases testosterone in human males. Proceedings of the National Academy of Sciences of the United States of America 108:16194-9.
    Tags: 
    behavior
    behavior genetics
    hormones

  • "I yam what I yam"

    Wed, 2010-07-07 00:28 -- John Hawks

    NEANDERTHAL MALES HAD POPEYE-LIKE ARMS

    This isn't normally the kind of story -- oh, who am I kidding? I love to snark on these kinds of stories!

    "Popeye-like arms". Hmmmm....

    Popeye the sailor man

    Neandertals had a low brachial index -- that is, with a short forearm were relative to the humerus. Popeye, well, you can see that he has the brachial index of a giant ground sloth. Neandertals were not built like Popeye.

    The article itself reports the ideas of a group of Russian scientists, who think that hormonal changes may explain the Neandertal pattern of muscle development and cortical bone strength.

    Remains of an early Neanderthal with a super strong arm suggest that Neanderthal fellows were heavily pumped up on male hormones, possessing a hormonal status unlike anything that exists in humans today, according to a recent paper.

    ...

    The mixture [of big muscles and highly mineralized bones] is puzzling, because "Neanderthals demonstrate a markedly androgenic constitution," meaning they seemed to have a lot of steroids, yet these same hormones can cause reduced mineralization.

    As a result, the researchers say "Neanderthals were characterized not only by peculiar biomechanical adaptations, but also by a specific hormonal condition which has no close parallels among modern human hormonal conditions either normal or pathological."

    There's no mechanism being proposed here, the androgen system has effects all over the body. This is not a testable hypothesis, it's really just a speculation.

    Or is it? The cool thing about having a Neandertal genome is that in principle we can look for differences in systems like the androgen receptor pathway. Looking for coding changes in androgen-associated genes is really just a browser window away.

    So I did some checking.

    Now, let me put some caveats here. This is good blog material, but the Neandertal genome sequencing has not reached a point where we can be at all certain about mutations. There are many gaps with no coverage at all in any Neandertal individuals. Most of the sequence of human coding regions is covered by at least one read, and a good fraction of sites have multiple Neandertal reads. As I've been looking through sequence, I tend to think a site may be interesting if it has a change in the Neandertal relative to the human sequence, and if it's not near the end of a read. If the same change is present in multiple Neandertal reads, that makes it a good candidate for a genuine change in Neandertals relative to the human sequence. A large fraction of those Neandertal-specific changes actually aren't Neandertal at all. They're shared with chimpanzees and represent new human-specific changes. Many of those are SNPs in humans where the genome draft has the derived version; there are also sites where the Neandertal shares a derived SNP allele with some other humans. Then there are ones not in chimpanzees or humans, which might be Neandertal-specific alleles or substitutions.

    Looking at the androgen receptor gene and the 5-alpha-reductase gene, both central to the androgen pathway, there aren't any interesting-looking sites in the Neandertal sequencing reads. I don't think the data refute the hypothesis that the Neandertals were like humans for these genes. That's just a little bit of looking, of course, and that particular fishing expedition wasn't likely to turn up anything new. But that's the point! We shouldn't just go off speculating about fundamental changes in hormonal biology in Neandertals anymore. We can look.

    That is just the beginning of answering a question like this. To test the hypothesis, we'd want to check many other genes that lie between the androgen receptor and its final effects on gene transcription. And of course, coding changes aren't the whole story of evolution in Neandertals. Promoter and enhancer changes, or even alternative splicing changes, may be more important than coding changes, especially for a system so broadly represented in different tissues. They're harder to look for by just firing up the genome browser.

    But even these kinds of changes are potentially testable. It's not quite as fast as an interview with a reporter, but it doesn't take days to look.

    Tags: 
    muscle
    Neandertal DNA
    Neandertals
    hormones

  • Attractive women have high estrogen?

    Fri, 2005-11-04 23:06 -- John Hawks

    This BBC story covers this paper (warning! PDF!) that found a correlation (r = 0.48) between attractiveness and estrogen level in women:

    The findings make evolutionary sense - men are attracted to the most fertile women, the University of St Andrews team told a Royal Society journal.

    Oestrogen levels during puberty can impact on appearance by affecting bone growth and skin texture, they said.

    ...

    The team of psychologists at the University's Perception Lab photographed 59 young women's faces aged between 18 and 25 and analysed their sex hormone levels.

    They then asked 30 volunteers - 15 male and 15 female - to rate the faces according to attractiveness.

    Both male and female volunteers rated the faces of the women with the highest hormone levels as the most attractive.

    My first reaction was that it just seems so...unlikely.

    My more studied reaction is that I'm not sure that the results are as interesting as they look at first glance. The paper is conservative in its interpretations -- much more so than the comments in the BBC article would suggest.

    The general idea is that males want to be able to assess female fertility, and if they can "read" estrogen levels through facial characteristics (which they perceive as "attractiveness") then it should have been adaptive.

    This argument would have to be based on two correlations: a correlation between "attractiveness" and estrogen level during facial development, and a correlation of estrogen level during facial development and fertility. This paper reports the first of the two.

    The second is (as far as I know) unknown, although there may be some hints in the opposite direction. There is this paper for example, describing the effect of estrogen treatment to reduce final stature in tall girls (estrogen promotes early epiphyseal fusion):

    Fertility problems were more prevalent in women previously given estrogens to lessen their adult height....Among women attempting to become pregnant for the first time, the likelihood of conceiving every month was much lower for treated than for untreated women ( Fig. 1). Women treated for tall stature had a significantly lower age-adjusted per-cycle rate of conceiving a first pregnancy. Fecundability was impaired both in women treated with DES and those given EE, and the timing of treatment (before or after menarche) and its duration did not influence the findings.

    It seems to me that if pubertal estrogen levels influence fertility, the strongest effect should be on the age at menarche -- since that influences the reproductive lifespan.

    Menarche would be a much more important reason for men to be able to assess estrogen levels in developing women. In small human groups, most men probably would have had a very good knowledge of all the women who would be potential mates. Attractiveness might have made some considerable difference to mating decisions, but these would also have been subject to many other constraints. On the other hand, it would be of great value to be able to accurately assess when new maturing young women would become available to mating. A young woman would likely be well-served to provoke some competition between males. Signaling maturity through physical changes would be a way to spur this competition -- which in many cases would have played out over many months or even years.

    A major influence on age at menarche is fatness, and fatness is related to estrogen levels in older women (Kaplowitz et al. 2001). Fatness may also significantly affect assessments of attractiveness, although not in an obvious way. I would guess that a slightly fuller face would be generally regarded as more "feminine", and in the study "feminine" ratings were correlated (r=0.97) with attractiveness. Certainly the average physiognomy of the 10 high-estrogen women in their sample has a fuller face than the average of the 10 low-estrogen women:

    Left: 10 highest-estrogen average face. Center: 10 lowest-estrogen average. Right: Actress Lindsay Lohan giving come-hither look.

    On the other hand, facial fullness -- especially in the lower face -- may not be a good guide to fatness generally. It's all just so confusing!

    The pictures do give a good hint to the "make-up effect" that the article discusses:

    "The findings about make-up are also interesting. The implication is that women are employing a deceptive strategy. They can fool the male visual system with make-up."

    Yeah. They appear to fool "love bugs", too.

    Tags: 
    development
    hormones
    evolutionary psychology
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Neandertals

For years, I've worked on their bones. Now I'm working on their genes. Read more about the science studying these ancient people.

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Malapa

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