Skepticism is good, but…

Well-informed skepticism is the best!

Earlier this week, Eric Michael Johnson drew my attention to a post by psychologist Christopher Ryan at his blog Sex At Dawn.  Ryan attacks Lovejoy’s monogamous humans model by citing many different lines of evidence.

I became so distracted by the reported testes:body mass ratio of 1/160 in humans that I couldn’t stop until I had some answers.  I am a female human, but even I thought that 1 kg of testicles would be an awful lot to lug around.  So I got out my books and my calculator and did some math, wrote in, and it was fixed.  Peer review in action!

But then I clicked through to the actual post, and realized that it didn’t get much better from there.  Apart from characterizing Ardi as mere “bits of bone,” Ryan displays many instances of ignorance.

First, a few things that Ryan gets right:

  1. Yes, reduced male-male competition can happen in promiscuous mating systems (but I do think that characterizing the Chimpanzee as having reduced competition is dubious).
  2. Humans are probably able to produce more sperm per ejaculate than the number that Lovejoy cites.
  3. Reproductive anatomy and physiology is particularly labile, so postulating about reproductive physiology 4.4 million years ago is a risky undertaking.

But then…

Lovejoy writes that “Humans have the least complex penis morphology of any primate.” Unfortunately, he never defines what he means by “complex;” nor does he discuss the fact that the human penis is, by most measures, the longest, thickest, most prominently displayed penis among primates. No mention of the unusual flared head or the external scrotum—both strong indications of sperm competition in our species.

Lovejoy clearly states that humans lack “keratinous penile surface mechanoreceptors” (known to you and me as penis spines and ridges) and an os baculum.  So there’s your complexity.

Lovejoy also states in the footnotes:

Flaccid human penis length (13 cm) is unusually great for a hominoid. Length is ~4 cm in Pongo and 3 cm in Gorilla. Its erect size is greater in the multimale Pan (8 cm), but this reflects specialized adaptation to penetrate seminal plugs. Short notes that “(e)ven the pubic hair in the male [human] seems designed to draw attention to the genitalia, rather than to conceal them as in the orangutan and gorilla.”

Lovejoy states these things in support of a rather weird argument against hand-to-hand combat in human ancestors, but why not in the discussion of sperm competition?  Because a huge penis does nothing if you don’t have the testes to back it up!  Clearly a large, pendulous, prominently-displayed penis is something special in humans, but it is not about sperm competition. The external scrotum- by itself- may be indicative of sperm competition, but combined with the fact that human testes are smaller and have fewer seminiferous tubules, that the human sperm midpiece volume is low, and that we have lost the physiology for creating copulatory plugs indicates that there may be something else at work here.

Perhaps the most glaring mistake lies in Ryan’s argument about canine teeth:

For example, much of his thesis hinges on the absence of pronounced canines teeth (fangs) in the fossils found. He writes that we can assume that both males and females lacked these canines (even if the teeth were from a female) because “The SCC [sectorial canine complex] is not male-limited; that is, it is always expressed in both sexes of all anthropoids….” But this is wrong. Male bonobos have long canines, while females don’t (2, 3). Lovejoy also claims an association between reduced canines and pair-bonding, but as this photo of the skull of a monogamous gibbon demonstrates, even this claim is suspect.

When anthropologists refer to the canine complex, they are not merely referring to canine length.  The Sectorial Canine Complex, or the CP3 complex, or the “honing” complex all refer to the way that the top canine tooth fits in with the lower canine and premolar.  It fits in this way in order to sharpen the canine tooth so that it acts as a blade.  In contrast to what Ryan states, both male and female anthropoids (including the bonobo) WILL have this trait if it is present at all.  Yes, the tooth will be longer in males (in many cases, much longer), but the sexual dimorphism here is in size, not in the actual way that these teeth occlude.

Teeth from more than 35 individuals have been found, and not one of them exhibits this Sectorial Canine Complex, so I think it’s safe to say that Ardi and her pals didn’t have it.

gibbon-teeth-2009And then there’s that beautiful gibbon skull.  Unfortunately, the canine monomorphism in gibbons actually supports Lovejoy’s whole thesis:  In monogamous species, the canine teeth are no longer under strict sexual selection, and natural selection can take over and do its thing.  In gibbons, this has meant that not only do males have large canines, but females have them as well.  Both males and females defend their territory, and so both have enlarged canines.  In humans, the argument is that the energy that goes into maintaining large canine teeth and getting into the fights that result when you have them could be better spent by gathering food for your partner and offspring.  As a general rule for primates, the canines don’t have to be reduced to indicate pair-bonding, but if they are the same in both sexes, something is up.

Lovejoy’s hypothesis is controversial.  It’s a Theory of Everything, and that should raise flags in everyone’s head.  But at the end of the day, it’s really stinkin’ weird that human males abandoned their canine teeth, and it’s really stinkin’ weird that human females abandoned their ovulatory advertisement.  I think monogamous pair-bonding goes further than any other hypothesis in explaining those two weirdnesses of the human.  However, my little red flag pops up when we connect those things to bipedalism.

Zingeser, M. (1969). Cercopithecoid canine tooth honing mechanisms American Journal of Physical Anthropology, 31 (2), 205-213 DOI: 10.1002/ajpa.1330310210
Lovejoy, C. (2009). Reexamining Human Origins in Light of Ardipithecus ramidus Science, 326 (5949), 74-74 DOI: 10.1126/science.1175834
Frisch, J. (1963). Sex-differences in the canines of the gibbon (Hylobates lar) Primates, 4 (2), 1-10 DOI: 10.1007/BF01659148
Leutenegger, W., & Kelly, J. (1977). Relationship of sexual dimorphism in canine size and body size to social, behavioral, and ecological correlates in anthropoid primates Primates, 18 (1), 117-136 DOI: 10.1007/BF02382954

About these ads

37 responses to “Skepticism is good, but…

  1. EMJ October 17, 2009 at 9:59 pm

    Excellent post Zinj! The problem with Lovejoy’s position is that the majority of human societies are not monogamous. Murdock’s Ethnographic Atlas found that nearly 3/4 of the human societies studied were polygynous. Our own society is far from monogamous with about 1/4 of all children born to unmarried mothers who were not cohabiting with the father (Bergstrom 1994) and estimates range between 5-10% that all children have been sired by men other than a woman’s partner.

    Across societies estimates of marital infidelity range from 26 to 70 percent for women and from 33 to 75 percent for men (Shackleford and Buss 1997). With the rate of divorce based on infidelity being what it is (about 25 – 50 percent of all marriages depending on the country), and the rate of extra-pair copulations being so high, it would seem that monogamy would hardly be the word to describe our own society, let alone the human species as a whole. While we clearly do not show the kind of promiscuous sexual behavior that chimpanzees or bonobos do, we’re not socially monogamous gibbons either. We lie in between.

    Great work, I look forward to seeing how this debate over Lovejoy’s theory continues to play out.

    I don’t know if you allow hotlinks, so full URLs of citations are below:

    Bergstrom (1994): http://ideas.repec.org/p/els/esrcls/042.html
    Shackleford and Buss (1997): http://www.academicarmageddon.co.uk/library/shack.htm

    • zinjanthropus October 17, 2009 at 11:49 pm

      Yes, this is a very interesting counter to Lovejoy’s hypothesis: humans are not monogamous. But I’m not sure if that is as damning as it seems. Orangutans were probably not solitary apes during Ardi’s time, either.

      I think that a lot of the controversy here comes from the idea that the hypothesis seems to be saying something about human social systems today, in the present. But Lovejoy’s hypothesis is an Origins idea. Clearly, we’ve deviated substantially in many other ways- we no longer have grasping feet, and our brains have increased like crazy- so I think it’s to be expected that we’d deviate from our pair-bonding origins, too.

      Like I said above, I’m not ready to accept the hypothesis at face value, but I do think it’s very interesting.

      • EMJ October 18, 2009 at 5:56 am

        I agree that Pongo’s current solitary lifestyle is likely a more recent adaptation and that they’re ancestors were more gregarious. However, I strongly disagree that Lovejoy’s goal is only in seeking origins. He uses multiple studies of modern humans to emphasize his argument for monogamous pairbonds (sperm competition, genital morphology, neuroendocrinology). What’s very curious is that he ignores the sexual dimorphism in Homo erectus (in fact, ignores the species altogether).

        Sexual dimorphism may not be a strong predictor of mating system anyway. Owens and Hartley (1998) show that many monogamous species that display biparental care are highly dimorphic while others that are extremely polygynous are monomorphic in both size and coloration.

        I salute Lovejoy for attempting to bring all of this information together for a unified theory, but I remain unconvinced that “Man the Provider” offers any more explanatory power than “Man the Hunter” or “Man the Toolmaker.” It’s yet another argument claiming that males were the progenitors of evolutionary “progress” while females were the passive recipients. I think it’s notable that no one else wanted to put their name on the paper with him.

    • Black Iris October 11, 2011 at 7:05 pm

      1. I think the contrast is not monogamous versus polygamous so much as monogamous versus promiscuous. Chimpanzees don’t form pair bonds with one or multiple partners

      2. When it comes to human societies, the vast majority of them practice female monogamy. Females have a mate and they have only one.

      3. Most men in most societies practiced monogamy. Polygamy is usually a privilege for powerful or wealthy men.

      4. Monogamy is about more than whether or not individuals sometimes cheat. If most people form pair long-term bonds to just one individual, it’s a monogamous system.

      5. Our modern society isn’t a good measure of what our ancestors were like, particularly when it comes to something like single motherhood which just wouldn’t have been possible.

  2. EMJ October 17, 2009 at 10:05 pm

    * That should read 5-10% “of” all children.

  3. Christopher Ryan October 17, 2009 at 10:17 pm

    Thanks for your response to my comments on Lovejoy’s paper. Having neither time nor energy for a prolonged debate on technical matters about which I am admittedly not an expert, I’d like to just make a few points in defense of my argument:

    — You write, “Humans are probably able to produce more sperm per ejaculate than the number that Lovejoy cites.”

    Probably, since the number Lovejoy cites is 100X below the number actually given in the paper he claims as his source.

    — You repeatedly refer to the “Sartorial Canine Complex,” but I found no reference to this when I Googled it. Do you mean the “sectorial canine complex,” the term both Lovejoy and I used? If so, Lovejoy writes that, “The cardinal indicator of male-to-male agonism in hominoid primates is the SCC. It is regularly employed during both territory defense and dominance disputes. Hominids are often characterized as having reduced canine dimorphism. Such reduction is only a secondary consequence of the primary hominid character, which is elimination of the SCC in its entirety.”

    It seems doubtful that any particular dental “occlusion” would be of much use in territory defense and dominance disputes. But if you find my interpretation uninformed, I refer you to John Hawkes, a paleoanthropologist who knows far more about these matters than I do, and who also takes Lovejoy to be talking primarily about canine size, not occlusion: http://johnhawks.net/weblog/fossils/ardipithecus/canine-non-reduction-gibbons-2009.html

    — You write: “Lovejoy clearly states that humans lack “keratinous penile surface mechanoreceptors” (known to you and me as penis spines and ridges) and an os baculum. So there’s your complexity.”

    Is this definition of penile complexity generally accepted among primatologists? I don’t think so. In fact, there’s a large body of literature in which the coronal ridge, unusual penile length and girth, and strangely underutilized spermatogentic capacity in the human male genitals are all seen as evidence of sperm competition in our species.

    You also appear to be unaware of considerable genetic evidence supporting sperm competition in humans, in addition to the papers I cited in my blog piece. For example, Kingan, et al., conclude that although, “Predicting the expected intensity of sperm competition in ancestral Homo is controversial, … we find patterns of nucleotide variability at SgI in humans to resemble more closely the patterns seen in chimps than in gorillas.”

    Add to all this the external, vulnerable scrotum (very unusual in a species not engaged in sperm competition), and it seems to me that reducing “complexity” to spines, ridges, and an os baculum is questionable, at best. Complexity is a broad concept and while I’m far from an expert on this material, I could go on for many pages concerning research about which you seem to be unaware.

    — You write that it’s “really stinkin weird that human females abandoned their ovulatory advertisement,” apparently unaware that it is an open question whether or not this is the case (see Haselton et al., for example). It may be that olfactory and behavioral cues have simply been ignored by researchers until recently.

    In summary, while I value the opportunity to learn from someone who has more specialized knowledge of this material than I do, I find your argument to be less than overwhelming, and your dismissive claim that mine contains “many instances of ignorance” to be unwarranted.

    Christopher Ryan

    References:

    Haselton, et al. (2007). Ovulatory shifts in human female ornamentation: Near ovulation, women dress to impress. Hormones and Behavior, 51: 40-45.

    Kingan, S. B., Tatar, M. and Rand, D.M. (2003). Reduced polymorphism in the chimpanzee semen coagulating protein, Semenogelin I. Journal of Molecular Evolution, 57: 159–169.

    • zinjanthropus October 17, 2009 at 11:36 pm

      I aplogize if you took offense to the word “ignorance.” I should have said something more polite, such as “unawareness.”

      But I do continue to find your interpretation very uninformed- particularly in regard to the SCC. If you don’t think that the SCC/honing/CP3 complex is useful in territorial or dominance disputes, I invite you to peruse any introductory primatology or biological anthropology textbook. At any rate, your original argument was this:
      “The SCC [sectorial canine complex] is not male-limited; that is, it is always expressed in both sexes of all anthropoids….” But this is wrong. Male bonobos have long canines, while females don’t”
      You confused the SCC with canine length, and then asserted that Lovejoy was wrong. He wasn’t. Your quote from him above clearly demonstrates that he is making a distinction. Anyone else who fails to make that distinction is mis-reading his argument.

      I’m not sure if primatologists have ever had a sit-down and thought about just how to define “penile complexity,” but I’m pretty sure that spines and a baculum would be included in a robust definition.

      I am aware of the genetic research pertaining to seminal proteins. There is a very strong selective sweep in Chimps, pseudogenization in Gorillas, and stasis in Orangs. Humans have none of those things, so they are very hard to interpret. I find this paper to be quite informative.

      As for olfactory and behavioral cues, I am certain that those things DO play a very important role in human mating. In fact, I’ve written about it here. But when I referred to ovulatory advertisement, I was referring more to the anthropological and primatological definition- sexual swellings. I should have been more specific. Human females have certainly lost the characteristic swellings that are typical of old world primates, and why they have done so is a very interesting question. Lovejoy’s answer is not necessarily the correct answer, but I think it’s an interesting hypothesis.

      • Christopher Ryan October 18, 2009 at 12:13 am

        It’s frustrating to debate with someone who insists that my disagreement can only be due to my ignorance. I referred you to Hawks (whom I see listed in your preferred links above). You ignore the fact that he shares my interpretation of Lovejoy’s point and instead dismissively refer me to “any introductory … textbook.”

        Are you capable of debate without resorting to insult?

        A baculum and penile spines may be “included in a robust definition” of penile complexity, but are not the definition thereof, as you argued previously: “There’s your complexity.”

        I’m not sure what “anthropological” definitions of ovulatory advertisement refer to sexual swellings, in that no humans (by your definition) have them and, as far as I’m aware, anthropology is the study of humans. You don’t seem to be referring to the genital echo theory, because you refer to these swellings as having been “lost.”

        Please note that while I was critical of Lovejoy’s paper, I didn’t imply that he was uninformed or ignorant. I was more interested in how factual errors weren’t caught by his editors and peer reviewers, which was the focus of my original piece. We’re all capable of making mistakes, as both you and I have demonstrated, so maybe we shouldn’t assume that disagreement necessarily implies ignorance.

      • zinjanthropus October 18, 2009 at 1:14 am

        Honestly, I meant no insult. You obviously have a very high level of knowledge- much higher than I would have if I were to venture into the field of psychology.

        If John Hawks allowed comments, I would have left one on his page, too, for failing to distinguish between SCC reduction and size monomorphism. It’s not a trivial point.

      • John Hawks October 18, 2009 at 5:41 am

        If John Hawks allowed comments, I would have left one on his page, too, for failing to distinguish between SCC reduction and size monomorphism. It’s not a trivial point.

        I agree. Lovejoy conflates them. Hence, my comment that things are not so simple.

        We have also known for thirty years that some australopithecines had substantial dimorphism of the SCC. LH 6 is no small canine, nor are the canines of STW 252. P_3 morphology is notably variable in early hominins, and in particular females tend to be more sectorial — one of those odd facts that every now and then is brought out as an argument for multiple species at Hadar. I don’t have any strong opinion, but I wouldn’t be surprised if canine size dimorphism *adjusted for canine size* is just as great in Ardipithecus as in bonobos.

        Every example in primates is perilous, because behavior-dental correlations, while real, are far lower than 1. But it seems to me that the gibbons are a pretty clear example showing that pair-bonded mating systems don’t cause canine size reduction.

      • zinjanthropus October 20, 2009 at 1:35 am

        Are the females are more sectorial than the males, or that they are more sectorial than would be expected for a female primate? I’ve never seen casts of those guys.

        I think that gibbons are an example that size reduction is not required, but that monomorphism usually results from pair-bonding.

      • Christopher Ryan October 18, 2009 at 11:52 am

        No harm done. At least you stimulated some debate (even attracting the attention of my very own internet stalker, who has nothing better to do than Google my name and pop up with the same anonymous insults wherever I go). I’ll continue to follow your blog. Maybe that’ll help me overcome the deficits in my “New-Age” education!

      • AK October 19, 2009 at 9:15 am

        No need to take these things so personally Christopher. zinjanthropus was merely pointing out the errors in your evidence and I was merely compensating for your misrepresentations. All in the interests of accuracy and the scientific method. Best that you get used to it eventually.

  4. rich lawler October 17, 2009 at 10:22 pm

    Nice post.

    I’ve never heard the phrase “sartorial canine complex.” Do you mean “sectorial?”

    Personally, I like Lovejoy’s hypothesis in that it specifically does try to connect various unique human features/behaviors. I’m not saying it’s correct, but there are useful ways of being wrong.

  5. razib October 18, 2009 at 3:36 am

    eric, i think you overestimate paternity uncertainty. see kermyt anderson’s 2006 paper.

    also, there’s a big difference between cultural ideals of polygyny and realized polygyny. and evolutionarily i think the ratio of male to female reproductive skew is a better index of polygamousness than cultural preferences…and the genetic data are long term effective male and female populations are currently confused (if we’re very polygynous obviously male effective population should be way smaller than female).

    but the big issue is that there’s a lot intercultural variance here. polygyny is pretty obviously leaving a huge genetic impact on some groups of PNG if you look at variance in their Y vs. mtDNA, but not so much in other groups.

    • EMJ October 18, 2009 at 5:19 am

      Yes, I know Anderson’s study but there’s good reason to be skeptical of his findings. Lumping together studies from the 1940s to the 1990s (many with differing methodologies) and then taking a median value isn’t very instructive. Plus, the 2-3% he reports is only for men with high paternity confidence. It extends to 30% for partners with low paternity confidence. There have been reports from China estimating values as high as 1/3 of paternity tests demonstrating cuckoldry. I don’t trust the high end values exceeding 10% either. So I’ll remain conservative.

  6. AK October 18, 2009 at 8:03 am

    It’s interesting to see Mr Ryan whinge about insult when he himself habitually insults researchers that he chooses to criticize. On his own blog, he has equated author’s with Rush Limbaugh and suggested that they “don’t get laid enough to understand their own conclusions.”

    As he has demonstrated here, he is extremely sensistive to criticism about his own background knowledge. By his own admission, his higher learning degrees are from a New-Age, online university (Saybrook), clearly bereft of the rigorous training required for comprehending the complexity of these matters, and he has no professional experience working as a psychologist nor any previous affiliation to any university.

    Yet he claims to be an evolutionary psychologist while at the same time creating an escape clause that he’s “not an expert.” He lobs out harsh, authoritarian criticisms without humility, yet commits glaring errors in very basic science and discourse.

    None of this would be so offensive if he were less abrasive and more forthcoming about his own naivete in his assaults.

    In essence, he is a product of the internet age, in which anyone with a computer and a few books on their shelf can call attention to themselves without offering any true substance. I would agree with the author of this blog that a few introductory courses, at least, are in order.

    • EMJ October 18, 2009 at 8:19 am

      Your word choices strike me as being identical to someone posting as Annalee at my blog and others. You seem to have a vendetta against Ryan so I wouldn’t trust your opinion on this matter. As with all science related issues, an argument will survive or fail based on its internal logic and its basis in solid evidence.

      • AK October 18, 2009 at 9:17 am

        My vendetta is against shoddy science and amateurs who draw attention to themselves by erroneously attacking my colleagues and, further, casting a bad light on my profession. As you state, evidence-based arguments should stand on their own. However, too many people are susceptible to the logical fallacy of “argument from authority.” Statistically, Science is a reliable journal whereas you can be fairly certain that the Daily Mail is specious. Mr Ryan is the Daily Mail pretending to be Science, which I find offensive on many levels.

        All I ask is that people do exactly what the author of this blog does: Check the assertions. That’s not personal, that’s science and peer review. What’s more, given the source, it’s prudent.

  7. Knockgoats October 18, 2009 at 3:53 pm

    While we clearly do not show the kind of promiscuous sexual behavior that chimpanzees or bonobos do, we’re not socially monogamous gibbons either. We lie in between the sheets. – EMJ

    I think you left off the last two words of your comment ;-)

    Nice post. Given how different socio-sexual systems are between chimpanzee and bonobo, there was surely time for several switches of strategy by both sexes between Ardi and ourselves (assuming, of course, that Ardi is our direct ancestor).

  8. Christopher Ryan October 18, 2009 at 8:08 pm

    FYI: Frans de Waal has just weighed in on Ardi again, specifically commenting on Lovejoy’s interpretation of the canine issue:

    “Whereas the chief anthropologist on the Ardi team goes by the bonobo-like name of Owen Lovejoy, he focuses all of this attention on the chimpanzee, as is tradition in his field. Since chimps are violent and Ardi probably wasn’t, he argues that we have a totally unique creature on our hands. His pet theory is that this must mean that Ardi and her contemporaries were monogamous, but unless the diggers come up with a male and female fossil holding hands and having wedding rings, the idea that these ancestors avoided conflict through pair-bonding remains pure speculation. There is no evidence for it, and the only pair-bonded primate we have in our direct lineage (the gibbon) has in fact huge canine teeth.”

    Read more at: http://www.huffingtonpost.com/frans-de-waal/was-ardi-perhaps-liberal_b_325201.html

    • EMJ October 18, 2009 at 8:58 pm

      Thanks for linking to de Waal’s article. It’s excellent.

    • zinjanthropus October 20, 2009 at 12:55 am

      Again, he’s failing to acknowledge that gibbons do not have enlarged canines to engage in competition for mates. Gibbons of both sexes have enlarged canines in order to defend their territories. They have monomorphic canines. Like I said in the original post, it doesn’t matter if they’re big or small, so long as they’re the same in both sexes.

      Besides this, for the one example of a monogamous primate with enlarged, monomorphic canines (the gibbon- see the references in the post) there are many other examples of monogamous primates with monomorphic canines that are small, such as the Night monkey (Aotus) and the Titi monkey (Callicebus). If we learn nothing else from Ardi, we should at least learn that no extant ape should serve as an analog for humans and their ancestors, no matter how close or far it is from our “direct lineage.”

  9. Christopher Ryan October 19, 2009 at 11:39 am

    Hey AK, why do you hide behind pseudonyms? Where did you get your advanced degrees? Who are your “colleagues?” What is your “profession?” You imply that you’re a psychologist, or evolutionary biologist, but I’m betting you’re neither. You take great pleasure in demanding transparency from me while hiding your own identity. What’s the big secret? My cards are on the table. Where are yours? Time to put up or shut up, as they say.

    • AK October 19, 2009 at 1:38 pm

      Mostly because I have seen the personal nature in which you consistently respond to debate. But all in good time. You realize, of course, that none of this would be an issue if you didn’t claim to be a psychologist without having any certifications or licence, without having performed any kind of internship and without ever having been professionally affiliated to a university. Indeed, in your own words, you are psychologist simply because “anybody in Spain can call themselves a psychologist.” Such questionable ethics regarding disclosure do not engender a lot of confidence.

      Don’t get me wrong, I strongly believe in technology as an educational tool, but psychology is an interpersonal activity that cannot be learned exclusively sitting in front of a computer screen. Isn’t it curious how every other blogger who writes PhD in their bio includes the institution where they studied?

      What’s more, you also claim to be a teacher as somehow supporting your expertise. But I don’t think that teaching ESL really qualifies you to be any authority on psychology, evolutionary or otherwise.

      http://web.archive.org/web/20080322114930/http://www.inglesbarcelona.com/profesoringles.htm

      More humility, less aggression, more honesty. Try that and you should do much better in your endeavours.

  10. Doctor Science October 19, 2009 at 12:21 pm

    Because a huge penis does nothing if you don’t have the testes to back it up! Clearly a large, pendulous, prominently-displayed penis is something special in humans, but it is not about sperm competition.

    Good catch! Speaking only of extant humans, it’s my observation that gay men are more likely to be “size queens” than are straight women, while, judging by my spam filter, straight men are the size-queen-iest of all. I strongly suspect that intra-male signalling is involved. Richard Hatch of “Survivor” has said that the nudity for which he became famous was a strategy to impress and intimidate the other contestants, and that it seemed to work on the men but not the women. Annecdote, not data, of course.

  11. Bjørn Østman October 25, 2009 at 5:20 am

    But at the end of the day, it’s really stinkin’ weird that human males abandoned their canine teeth, and it’s really stinkin’ weird that human females abandoned their ovulatory advertisement.

    I wonder if the loss of canines could be linked pleiotropically to the changes in skull and jaw size?

    As for the loss of female advertisement of the buttocks, it has previously been hypothesized that it has to do with the benefit to her of keeping her mate guessing when she is ovulating; have sex all through the month, and keep him coming around for protection and food contribution.

    • zinjanthropus November 11, 2009 at 4:49 pm

      Yes, that is the idea behind the loss of advertisement, and Lovejoy’s monogamy hypothesis. Males who provisioned didn’t need to compete with their canines for mating anymore, and instead stuck with the same female all month (presumably, for longer). It sets up a very frustrating “chicken or egg” problem, though. Which came first: Loss of advertisement, or canine reduction?

      As for pleiotropy in canines, the Ardi dentition paper seems to rule out this possibility, because the rest of the jaw had not yet begun to reduce (and really, this didn’t happen in earnest until Homo). The molars had not yet become gigantic, either.

  12. Pingback: Four Stone Hearth 79 @ Anthropology.net « Anthropology.net

  13. KSUgrad December 11, 2009 at 3:54 pm

    Ryan: “It seems doubtful that any particular dental “occlusion” would be of much use in territory defense and dominance disputes.”
    You seem to be missing the point & the reason for distinguishing length from the SCC. Within a SCC the larger, projecting upper canine is constantly honed by occlusion against the lower third molar of anthropoid primates. This honing sharpens the canine making it a knife-like weapon used in territory defense.

    Ryan: “Humans are probably able to produce more sperm per ejaculate than the number that Lovejoy cites… the number Lovejoy cites is 100X below the number actually given in the paper he claims as his source.”
    What specific number & citation are you talking about? I quickly looked over Lovejoy’s paper again, but I failed to see him ever specifically cite any number.

    Ryan: “Is this definition of penile complexity generally accepted among primatologists? I don’t think so.”
    Of course there is no specific definition that states “male genitalia must possess this trait, this trait, this trait & that trait to be considered complex”. However, you’d be hard-pressed to find a primatologist that would say keratinous penile surface mechanoreceptors and an os baculum are not part of a complex penile structure, which humans lack.

    Ryan: “You also appear to be unaware of considerable genetic evidence supporting sperm competition in humans”
    I do not doubt that there are genetic papers supporting sperm competition in humans. Just as well, there are clearly papers on the flip side (just see Lovejoy’s paper for examples). However, I would be more careful how I interpret such papers. For example, “…we find patterns of nucleotide variability at SgI in humans to resemble more closely the patterns seen in chimps than in gorillas” does not actually support the idea that of sperm competition in humans. What is actually saying is that humans are in between gorillas & chimpanzees in this regard; but closer to chimpanzees. I assure that this fits perfectly well into the type of mating structure proposed by Lovejoy & is to be expected.

    Ryan: “Add to all this the external, vulnerable scrotum (very unusual in a species not engaged in sperm competition)”
    First, I’m not sure what the connection is that you are making between having an external scrotum & sperm competition. Personally, I don’t see one at all (probably because there isn’t one). What should have been much more notable is that having an external, vulnerable scrotum is a clear indication or reduced/absent male-male agnosticism.

    Ryan: “human females abandoned their ovulatory advertisement… [this] is an open question.”
    Not really… Human females have lost all visual advertisement (I hope at least we can agree on this much). The point in question is whether or not there are olfactory ques. Study after study show that when questioned on the matter humans (both males & females) are completely unaware as to when they are actually ovulating. But, olfactory ques could be subconscious. However, given the greatly reduced olfactory capabilities of humans, in order for a male to pick up on such ques he’d likely have to be spending a lot of time close to said female–sounds like a pair-bonded situation to me.

    Ryan: “…you refer to these swellings as having been “lost.”
    When looking at all other extant Catarrhines, It would take an extreme amount of parallel evolution for this not to have been the case.

    Hawks: “We have also known for thirty years that some australopithecines had substantial dimorphism of the SCC.”
    The problem with the examples you have given is that they are not contemporary. Should anyone be surprised to see widely varying dental measurements from specimens separated by thousands of years & (often) miles. In fact, the only assemblage we have that is not greatly separated temporally &/or spatially is AL-333. If you look within this single assemblage however, dimorphism is greatly reduced.

    Hawks: “females tend to be more sectorial”
    Which specific specimens are you talking about? I’ve certainly never seen this phenomenon or even heard such a claim before.

    Hawks: “But it seems to me that the gibbons are a pretty clear example showing that pair-bonded mating systems don’t cause canine size reduction.”
    You’re ignoring the fact that, although pair-bonded, gibbons are highly territorial. Lovejoy has actually pointed this out many times. See “Modeling Human Origins: Are we sexy because we’re smart, or smart because we’re sexy?” for an example.

  14. Bystander December 20, 2009 at 9:32 pm

    Does anyone know where to find Lovejoy’s responses to these mistakes/if he has any published responses? I’m having difficulty finding anything

    • KSUgrad December 21, 2009 at 2:50 pm

      I’m not sure what you’re asking exactly: do you mean mistakes made by Lovejoy or mistakes made by others interpreting Lovejoy?

      If you mean the latter, there are simply far too many people misinterpreting Lovejoy for him to address their criticisms directly (as there has been for the past 30 years). However, I should think that his paper in Science should be response enough on its own. For those that still do not understand, they need only read his paper for themselves (instead of someone else’s misrepresentation; see: EMJ’s http://scienceblogs.com/primatediaries/2009/10/grand_evolutionary_dramas_abou.php for a good example of this).

      If, however, you are referring to Lovejoy’s own mistakes, then I would ask you to be a bit more specific. I am aware of only one mistake: a typo which resulted in a misquote of Pierce & Breed (2001).

      Lovejoy wrote: spermatogenesis efficiency (daily sperm production
      per gram of testes), “varies from about 2.65 × 10^7 in rabbits to less than 0.06 × 10^6 in humans.”
      Pierce & Breed: spermatogenesis efficiency (daily sperm production
      per gram of testes), “varies from about 2.65 × 10^7 in rabbits to less than 6 × 10^6 in humans.”

      On the surface this appears to be a huge mistake as Lovejoy has stated that human spermatogenesis is far less than it actually is. However, while it is unfortunate that such a typo made it to the final print, it is ultimately irrelevant. As many others have pointed out, chimpanzee sperm production is much higher & remains higher after subsequent ejaculations as compared to humans. E.g., mean chimpanzee sperm production is 1278 * 10^6 [1]; easily more than 2 orders of magnitude higher than in humans, which is precisely what Lovejoy stated. His description & analysis remains valid either way.

      [1]J. Marson, D. Gervais, S. Meuris, R. W. Cooper and P. Jouannet (1989) Influence of ejaculation frequency on semen characteristics in chimpanzees (Pan troglodytes). J. Reprod. Fert.

  15. Robustus December 22, 2009 at 11:48 pm

    It is very troubling that John Hawks, on his website and within these comments, continues to fail to recognize the difference between canine size and the SCC (C/P3) complex. If you don’t understand that distinction, you have no business in debating the Lovejoy model.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 29 other followers

%d bloggers like this: