Penis Spines, Pearly Papules, and Pope Benedict’s Balls

The following guest post by Eric Michael Johnson is part of the Primate Diaries in Exile blog tour. You can follow other stops on this tour through his RSS feed or by following him on Twitter. If this is your first time visiting A Primate of Modern Aspect make sure to browse some of the other posts on the blog. Thanks. – EMJ

Do Nature‘s penis spines really separate humans and chimpanzees?

This post was chosen as an Editor's Selection for ResearchBlogging.orgThere is very little known about the reign of Pope Benedict III except that clerics were generally satisfied with his testicles. Upon his coronation in 855 AD God’s chosen messenger on Earth sat in a special chair resembling an ancient commode while the Holy See checked to make sure that the papacy was indeed infallible.

Two reliable clerics touched his testicles; witnesses who presented legal evidence of his maleness. . . At this the priest and the people responded, “Deo gratias” [Thanks be to God].

After all, you couldn’t be too careful. The Bible was very clear that, “He whose testicles are crushed or whose male member is cut off shall not enter the assembly of the LORD.” Healthy genitalia was a sign of spiritual purity and the Church made a point to check beneath the mantum of every Pope until up through the fifteenth century.

Of course, Christianity wasn’t alone in this respect. The ancient Greeks saw the penis as a gauge to their proximity with the Gods, the Hindu god Shiva is worshipped primarily by paying homage to his penis, or linga, and the Sumerian god Enki was thought to have brought life to the Tigris Valley when he “lifted (his) penis [and] brought the bridal gift.” The Pope seems to have merely been the latest in a long line of devout men who were dropping their pants for the Lord.

Now, scientists have gotten in on the act and have sought to understand human origins by studying our own little Bishop. From the standpoint of evolutionary biology this male obsession with their own genitalia makes perfect sense. Every animal alive today is able to stand and be counted because of a long line of ancestors who successfully reproduced. The natural world is a living erotic museum filled with variations in male genitalia, illustrating how natural selection has paid nearly as much attention to the male member as Catholic priests have.

But there’s a sinister side to this obsession, by which of course I mean penis spines. Throughout the Order Primates, as well as in many other mammal species, males have developed small (and sometimes not so small) keratinized structures along the head and/or shaft of their penis that have been adapted to maximize reproductive success. According to the, rather appropriately named, primatologist Alan Dixson in his book Primate Sexuality, these spines can be simple, single-pointed structures like in macaques or complex ones with two or three points per spine like in the prosimians (lemurs and lorises). These different forms of penis spine therefore suggest different mating strategies that various species have adopted during their evolution.

Examples of penile morphologies in primates. Note the obvious spines on I and K and the dots on N. Top row: Eulemur fulvus, Saimiri boliviensis, Macaca arctoides (stump-tailed macaque). Bottom row: Macaca fuscicularis (long-tailed macaque), Papio cynocephalus (baboon), Pan troglodytes (chimpanzee).

However, a new study in the journal Nature has generated a great deal of titillation this week as Cory McLean and colleagues have revealed a sequence of DNA that promotes these penis spines, a sequence that humans appear to have lost. The genetic mechanism involved has already been explained extremely well by Ed Yong and John Hawks. However, the interpretation of what the loss of this DNA reveals about human evolution is perhaps the most provocative claim and has resulted in a flurry of media attention.

“Simplified penile morphology tends to be associated with monogamous reproductive strategies in primates,” write the authors. According to their study, the loss of these spines would have resulted in a reduction in sexual sensation (because the spines are thought to be connected to nerve endings) and would therefore have allowed our ancestors to engage in more prolonged sexual activity that the authors associate with pairbonding and the evolution of social monogamy (citing Owen Lovejoy’s Ardipithecus ramidus paper from 2009 as a model).

As Nature News wrote in their summary of these results:

It has long been believed that humans evolved smooth penises as a result of adopting a more monogamous reproductive strategy than their early human ancestors. Those ancestors may have used penile spines to remove the sperm of competitors when they mated with females. However, exactly how this change came about is not known.

This is where it’s important to know precisely what it is that we’re talking about. Nature News referred to these structures in chimpanzees as “penis spikes” when the reality is more akin to goose bumps. Scicurious has posted a review of the only study that seems to have been done on these structures (published by W.C. Osman Hill in 1946) that found these “spines” to be only about 0.35mm wide, or the thickness of a human hair. Hardly a structure that would be useful for removing sperm.

Another problem is McLean et al.‘s argument that loss of penis spines would result in reduced sensitivity and longer bouts of sexual activity. As Dixson points out in Primate Sexuality (p. 118), orangutans have more elaborate penis spines than chimpanzees do and yet their average duration of sexual activity is significantly longer than either chimpanzees or humans. Chimps engage in sexual activity for an average of 8.2 seconds while the average for humans (based on Kinsey’s data) is less than 120 seconds. In contrast, orangutans range between a median of 840 seconds and a maximum of 2,760 seconds. Humans actually rank 14th in the duration of sexual activity (also falling behind macaques).

However, there’s a more serious problem with the argument presented in this study. The source the authors cite in support of their argument for smooth penis monogamy is Dixson’s Primate Sexuality, however he doesn’t discuss what penis spines indicate about primate mating systems in that book. That’s in his later book Sexual Selection and the Origins of Human Mating Systems, where his conclusions are somewhat different.

Four penile morphologies in single-partner or multi-partner primate mating systems (including humans). All categories show a significant difference except for penis spines.

As Dixson’s graph indicates, there are significant differences between a single-partner mating system (monogamy or polygyny) and a multi-partner mating system on three of the four categories: penile length, baculum length, and distal complexity. The only penis morphology type that isn’t significant are penis spines. This doesn’t necessarily invalidate McLean et al.’s argument for increased pairbonding, but it doesn’t support it either. It shows that there is no correlation between penis spines and primate mating systems, the correlation that McLean et al. is arguing for. In contrast, Dixson concludes that Homo sapiens is a polygynous species. However, other factors suggest that a multi-male multi-female system is more accurate given the diversity of human sexuality.

There’s also one final thing. Not all humans have lost their penis spines. Dating back to 1700 anatomists have identified what have now become known as pearly papules (also called Hirsuties coronae glandis). As reported by Denniston, Hodges, and Milos in 2009:

We have shown that, in the chimpanzee, these papules are a normal feature (spine-like) and are associated with nervous structures. It seemed to us that, in man, they may be a return to an earlier morphology.

To see a picture of these human “penis spines” click here [NSFW].

Five studies have been done involving nearly 2,000 patients in three separate countries, with an estimate that about 30% of all men develop these papules. In contrast, only four chimpanzees were studied in Hill’s 1946 paper on penis spines so it’s unknown how prevalent these structures are even within genus Pan. As Hill notes in his study:

The spines of the Chimpanzee are simpler structures than those of any of the other Primates, and the question arises as to whether they are degenerate remnants of a once powerful armature or a new product of evolution.

While the genetics of these pearly papules have yet to be studied, it doesn’t seem that a strong case can be made yet for significant differences between our two species on this point. John Hawks goes on to note that the chimpanzee version can even be implanted into transgenic human foreskin fibroblasts:

That indicates that the overall genetic system to make penile spines is still there lurking in our genomes. If we could turn on the gene at the right time, replacing the function of the enhancer, we can still grow penile spines.

I’m confident that the bulk of this week’s Nature paper will offer a host of tantalizing insights into the ways that humans and chimpanzees have travelled down different evolutionary paths since our common ancestry. At the same time, our evolutionary history has primed some members of our species to seek firm answers by looking to their respective, er, members. As we sit and try not to think about Pope Benedict’s balls, we can muse on how potential revelations may indeed develop from these investigations. But it’s also possible that we’ll only be greeted with a cold hand and a cheap thrill before moving on to the next study.

Image: Chimpanzee Pope by Nathaniel Gold.

ResearchBlogging.orgMcLean, C., Reno, P., Pollen, A., Bassan, A., Capellini, T., Guenther, C., Indjeian, V., Lim, X., Menke, D., Schaar, B., Wenger, A., Bejerano, G., & Kingsley, D. (2011). Human-specific loss of regulatory DNA and the evolution of human-specific traits Nature, 471 (7337), 216-219 DOI: 10.1038/nature09774

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101 responses to “Penis Spines, Pearly Papules, and Pope Benedict’s Balls

  1. Gaia March 11, 2011 at 8:59 pm

    Oh shit, I’ve lost my penis spines AND my penis – am I still human?

    Fantastic piece, Eric, perfect use of diagrams too. Very informative. Wishing I were a macaque for the first time…

  2. EMJ March 11, 2011 at 9:17 pm

    Thank you Gaia. Yes, I suspect you’re still human (though we should check in with St. Augustine on that point). Sorry if this post wasn’t particularly inclusive, but you know how men are when we get going on about our gonads.

    • Kapitano March 12, 2011 at 11:13 pm

      Do women have papules too? They have clitorises (clitorides, clitori…whatever) which are ‘modified’ penises (peni, penes?) so…do some women have residual spines?

      • edgarmanhattan March 13, 2011 at 9:29 pm

        Actually, penises are modified clitorises – without that burst of testosterone at the right time during gestation, XY babies end up with clitorises. Genetically, it’s the default organ.

        And yes, women have equivalent genetic expressions, called Vestibular papillomatosis by male researchers who assumed it was pathological. Typical.

      • Mrs. Ples May 5, 2011 at 10:25 am

        I’d wish to see an article about femal genitals and their functions and importance to reproduction! Hey it’s not a one way street and if the penises have different morphological features, it has somehow fit to the females structures as well, doesn’t it? And about the lenght of intercourse, it is also something two individuals take part in. No offense but it’s all too male centered for me. Anyway very well written and informative article! Thanks a lot!

      • primate May 5, 2011 at 12:43 pm

        Re. female genitalia – a few pictures here of the variation in external genitalia in some primates page 266:

        and some internal views of macaques here page 245:

        The ‘lock and key’ theory of female and male genitalia does not seem to be supported.

        In insects the male genitalia varies a lot – in some species the only way to tell males of different species is to compare the genitalia. One main view here is that the male-male competition has led to rapid evolution as males try to persuade females to use their sperm. Female insects can store sperm and seem able to choose which to use.

        In mammals sperm storage does not occur but ‘female choice’ is still likely to be a factor. What needs to be understood is that while females and males need to mate to reproduce, females have a lot of potential sperm to choose from while having limited eggs so will benefit from rejecting many males/sperm and this may be pre-copulation or post copulation. Males are trying to circumvent female mate choice and have their sperm used reagardless of female choice.

        So the evolution of genitalia is as much about a battle over fertilization as about a ‘fit’ between the sexes. The chimpanzees penis is ‘pointed’ to dislodge sperm plugs deposited by other males. Chimpanzee female mate choice seems to be more limited to their choice of which group they transfer to at puberty which is like a choice of a whole community of males who spend their whole lives together. The alpha males mostly get to mate when the female is ovulating.

        Other female mammals if they are able wiil reject males pre-copulation. Or choose a single male in the polygynous system. There is a red deer female on film who, when her harem male took a rest, sneaked off to another male and mated with him then returned to her own group, her male there none the wiser.

        The human penis length is probably due to the cervix being far inside the female and the male evolving to get as close as possible to the cervix. The female internal reproductive tract appears to have evolved to obstruct sperm so that only the highest quality makes it through – only one or two sperm make it to the egg in humans. And all kinds of chemical attacks and signalling goes on that we don’t yet know enough about.

        My tentative opinion on the girth of the human penis is that human childbirth and maybe bipedalism means that the human vaginal muscles would not get much enjoyment from a thin penis so females may well have selected for males with greater girth. The importance of female pleasure in humans and the bonding that this creates with repetitve mating with a preferred male does seem important – with evolution of bonding hormones in both sexes too. Also female orgasm seems at least, if not even more, as important to human males than to females and seems to be an important signal to the male of female satsifaction with him as a mate.

      • Penile Papules July 30, 2011 at 7:53 pm

        There might be similar skin conditions in women. There is a female form of PPP named vestibular papillomatosis. This vaginal skin condition is rare among women. This condition of the vulva occurs in females, and it is a normal variation of human anatomy.

      • asdfadsf May 22, 2013 at 2:00 am

        like they didn’t assume dick teeth were a disease or problem too? although vagina dentata is scarier

  3. David Dobbs March 11, 2011 at 9:46 pm

    Really nicely done. Not every day you see a man on fire toss cold water so skillfully.

  4. zinjanthropus March 11, 2011 at 11:46 pm

    Let me just say again (in public) that I LOVE this post. Penis spines are just about my favorite thing in the world, and you’ve managed to teach me something new about them. Thanks be to god, indeed!

  5. Christopher Ryan March 12, 2011 at 12:24 am

    Great piece. The NSFW penis spine picture appears to have been taken down though, FYI. I wonder if the testicle-checking in 855 had anything to do with the supposed reign of “Pope Joan” from 853-855. Recent scholars question whether there ever was a Pope Joan, but if they suddenly started checking the Pope’s junk in 855, maybe it really happened!

    More seriously, isn’t it amazing the twirling leaps otherwise cautious scholars will take to “discover” evidence for ancient monogamy in humans?

    • Eric Michael Johnson March 12, 2011 at 1:03 am

      Yes, it never ceases to amaze me. I haven’t had this much fun since Lovejoy.

      Thank you for the heads up about the image. I just discovered that myself. I found a temporary place to store it where it shouldn’t meet too many objections. It will soon be added to the link above:

    • Black Iris October 13, 2011 at 10:02 pm

      Why wouldn’t ancient humans have been monogamous? Our societies don’t look like chimpanzees with females openly having sex with multiple males and not bonding to any one male. Nor do they look like gorillas with one male monopolizing a group of females until he gets knocked off.

      With the little evidence we have on ancient humans or our relatives, why not monogamy?

  6. primate March 12, 2011 at 3:02 pm

    I agree that the penis ‘spines’ tell us little about mating systems. Probably a primitive trait and significant in non-gregarious/dispersed species such as the bushbabies and other prosimians but less so in monkeys and apes.

    The much more obvious difference between human and chimpanzee penis is the filiform morphology of the chimpanzee penis to, most probably, penetrate the copulatory plugs left by previous mates. See Dixson and Mundy on this here:
    “Sexual behavior, sexual swelling, and penile evolution in chimpanzees (Pan troglodytes)”

    See also “Rate of molecular evolution of the seminal protein gene SEMG2 correlates with levels of female promiscuity”
    Humans seem to fit with gorilla and gibbon in this respect.

    What is most strikng to me regarding the variation in penile morphology in primates is the similarlity between human and typical Old World monkey penises ie species where there are polygynous mating systems plus, of course, the females sometimes mating with extra-group males. These are the langurs, guenons and patas monkeys illustrated on page 252 of Dixson’s ‘Primate Sexuality’.

    • Black Iris October 13, 2011 at 10:23 pm

      What I’m getting from this is that human penises seem to suggest female monogamy, whether or not we look at spines.

      1. Chimpanzee penises are shaped in a way that would help them get rid of copulatory plugs because chimpanzee females sleep with multiple mates. Human penises are shaped differently suggesting that they aren’t engaging in sperm competition. That could just because humans don’t make copulatory plugs, or it could suggest that the females didn’t have multiple partners.

      2. In terms of molecular evolution of semen, humans are more like gorilla and gibbons than chimpanzees. Those are both species where females mate with one male, at least most of the time.

      3. Human penises look like those of langurs, guenons, and patas monkeys. The monkey species are polygynous – the females mating is limited.

      Is that what you’re saying?

      Also, why are penis spines/bumps probably primitive? In insect species they are an important part of sperm competition. Why wouldn’t they play that role in primates?


  7. primate March 12, 2011 at 3:18 pm

    Also this article is interesting:

    “Conservation of Y-linked genes during human evolution revealed by comparative sequencing in chimpanzee”

    “Why have X-degenerate genes decayed in the chimpanzee lineage but not in the human lineage? We speculate that X-degenerate gene decay in the chimpanzee lineage may be a by-product of strong positive selection focused elsewhere on the Y chromosome, through a process known as genetic hitchhiking. Because the Y chromosome does not participate in sexual recombination with a chromosome homologue, natural selection acts on the chromosome as a unit. Deleterious mutations in some Y-linked genes can be carried along, even to the point of fixation in a population, by physical linkage to strongly beneficial mutations in other Y-linked genes. In addition to their X-degenerate genes, primate Y chromosomes contain many families of ampliconic genes, which have testes-restricted expression patterns and critical functions in sperm production. Because of this central role in spermatogenesis, the Y chromosome’s ampliconic genes may be subject to powerful selective pressures especially in species such as chimpanzees where females usually mate with multiple males, the sperm of which then compete for a limited number of oocytes. During chimpanzee evolution some X-degenerate genes may have been casualties of selective forces directed at the Y chromosome’s ampliconic genes—forces that were not as intense during the evolution of our less promiscuous species. In the future, comparisons of sex chromosome variability in chimpanzees and humans may provide a test of this speculative hypothesis.”

  8. Rosemary Joyce March 12, 2011 at 4:07 pm

    Thank you for this! I was so irked by the weirdness of the coverage that I blogged about it twice, at Ancient Bodies, Ancient Lives and Psychology Today. Now I wish I had waited, since you not only have the graphics I was searching for, but the fabulous point that humans haven’t (entirely) given up on these structures…

  9. Pingback: More Penis Spines!! (or maybe that should be penis bumps) « Ancient Bodies, Ancient Lives

  10. primate March 12, 2011 at 5:22 pm

    Here is some of the chapter from ‘Primate Sexuality’ where you should be able to view at least some of the pages:

    Pages 250 and 251 have some more illustrations but unfortuately page 252 does not seem to be available and that shows the rather uniform, and very much human-like, penises of langurs, guenons and patas monkeys.

    From 261 is most of Dixson’s discussion of the evolution of penile spines.
    He discusses the five functions for penile spines proposed for rodents and says some of these may apply to primates.

    • Eric Michael Johnson March 12, 2011 at 10:53 pm

      Thanks primate. Sadly some Google Books aren’t available for people in Canada or I would have linked to the table I referenced about orangutan mating duration. The image on 250 is nearly identical to the one I provided from Dixson’s later book but, I agree, the images on 252 are quite striking. Dixson doesn’t provide an analysis of glans penis morphology which is strange. He shows those images and notes that most langurs, guenons, and patas monkeys are polygynous which fits with the argument he’s making. Why not include that in the four characteristics he tests in his later book? Makes me wonder what he left out.

      • primate March 13, 2011 at 8:51 am

        Glans morphology is ‘distal complexity’ – complexity of the distal regionre. overall shape – something he states as difficult to quantify in practice.

        I don’t have Dixson’s later book.

        Page 249 of ‘Primate Sexuality’ has the graphs for the four characteristics.
        He does discuss glans morphology of macaques and Pan page 251 and general variation in penile morphology for the langurs etc. on page 252.

        Looks like I’ll have to get his later book.

  11. megan March 12, 2011 at 7:01 pm

    Thanks for this Eric! I’ve been hunting down penis spine information as best I could since that Nature News ‘spike’ article got posted, and no one knew much – so I appreciate your research. Penis spines is a LOADED term even if it has a scientific meeting – to the rest of us it implies a pain that I’ve never seen a chimpanzee lady show. Thanks for clearing it up.

    • Eric Michael Johnson March 12, 2011 at 10:59 pm

      Absolutely. For Nature News to use that term was to completely distort the reality. I’m sorry to say it was poor science journalism, but it wasn’t an isolated incident and most news outlets treated this research uncritically and even exaggerated the findings. I wrote about a similar case in the “Meat for Sex” study that came out in 2009: For some reason, when journalists are talking about primate sex they can’t help themselves.

      • megan March 14, 2011 at 11:03 pm

        also, Eric, it seems like (and i could be wrong on this, I’m inferring from the blog pics) in primates these ‘spines’ tend to be clustered more towards the head of the penis – whereas the cat penises I’ve seen seem to be spiked more near the base and shaft Am I visualizing the primate penises right? If so – what types of animals have spines in this more limited location, and could that be part of explaining the difference in possible function? homologus or analogus spines here?

  12. MZD March 12, 2011 at 10:25 pm

    Ha ha! I still have spines and enjoying every one of them! Sucks to be you Mr. “Smooth N’ Bald”!

  13. zinjanthropus March 13, 2011 at 4:24 am

    Just as an FYI: A lot of the comments with links are being sent to my spam folder (as well as a LOT of legitimate spam), so if your comment doesn’t show up immediately, I’ll approve it within a few hours (as long as you’re not trying to enlarge my penis).

  14. megan March 14, 2011 at 10:57 pm

    As an aside, between this topic, and the previous post by Zinj on penis shapes, I think this could make a very fun, interesting AND useful cross-sub-disciplinary AAA session on sexual behavior and bio-cultural evolution. Toss in some stuff on the loss of estrus swellings and the presence of female orgasm and I’m sold.

  15. An Old Timer March 15, 2011 at 5:41 am

    Hilarious, if it’s on the level– for quite a while, I thought it was an April Fool’s Joke, and I’m still not sure. If all the technical references are authentic [and I’m still considering the possibility that they’re made up! :-) ] a brilliant piece of research, all the more so because it’s so funny.

  16. Pingback: Wednesday Round Up #146 | Neuroanthropology

  17. Spines vs Papules March 16, 2011 at 4:38 pm

    Enjoyable blog post! But after doing some research, it is worth clearing up one point: Penile spines and Pearly Penile Papules are very different structures.

    Despite the superficial resemblance between pearly penile papules and spines (PPP), the structures are actually quite different at the cellular level.
    *You can see high magnification images of the structures here from the group that did the genetics work:
    The site explains:
    “In mice and chimps, penile spines are small projections made from the local piling up of cell layers in the outermost keratinized epidermis of the skin (top row).

    In contrast, a PPP in humans consists of a larger out-pocketing of the entire skin, without local layering of the keratinized epidermis to make hook-like projections, and with the bulk of the overall structure consisting of a dense, well vascularized core of connective tissue cells, rather than epithelial cells (bottom panel).

    In addition, while mouse and chimp penile spines are often closely associated with neural sensory structures, human PPP do not appear to be enriched for neural cells (Glicksman and Freeman (1966) Arch. Dermatology 93: 56-59).

    PPP are an interesting morphological variant in humans. However PPP are structurally distinct from the typical penile spines found in mice and chimps, and likely form by very different, still poorly understood mechanisms.”

    Thus, there does in fact seem to be a very strong case for differences in development and morphology between chimpanzee and human, with respect to penile spines and pearly penile papules.

    • primate March 16, 2011 at 5:28 pm

      That’s really useful and important info on this as there have been lots of questions about these PPPs in relation to the spines on other primates.

      • Eric Michael Johnson March 16, 2011 at 8:32 pm

        Yes, there have been a lot of questions about these structures. As I was digging into the literature on this many authors associated PPPs as being similar to the penis spines found in other primates, so I don’t think there is a clear consensus one way or the other on this point. There may be more similarities than the information at the Stanford site reveals. At least two studies describe human PPPs as keratinized structures made up from outer layers of the epidermis.

        Hyman, A. F. Tyson’s “Glands”. Archives of Dermatology 99, 31 (1960).

        Ferenczy, A. et al. Pearly penile papules: Absence of human papillomavirus DNA by the polymerase chain reaction. Obstetrics & Gynecology 78, 118-122 (1991).

  18. Blackbird March 17, 2011 at 12:33 pm

    Very helpful post. In conclusion, probably both chimps and humans have penile spines with the same functional significance than the appendix, therefore the deletion in humans could be part of many other genes/regulatory regions that lost their funcion in the common ancestor or earlier. But what about the whiskers? the paper authors claim chimps have whiskers? what are they talking about here?

    • primate March 17, 2011 at 12:47 pm

      I was going to mention whiskers.
      My original response to this paper was how on earth I did not come across chimpanzee penile spines before, but there is the same response to chimpanzee whiskers.
      What I have concluded is that the spines and the whiskers are primitive traits in other mammals and primates (mice are in the paper, I think) that are already virtually gone by the time we get to chimpanzees.
      Can’t see the actual paper so it is a bit frustrating not being abe to see exactly what is said about chimpanzee spines and whiskers.

      • Blackbird March 17, 2011 at 7:06 pm

        We actually did the McClean paper in our Journal Club today, so I had a look at the paper they cite supporting that chimps have whiskers.
        (Muchlinski, M. N. Acomparative analysis of vibrissa count and infraorbital foramen area in primates and other mammals. J. Hum. Evol. 58, 447–473 (2010).) Despite being published in the Journal of Human Evolution, humans are not mentioned or investigated (!). The author distinguishes between macro and microvibrissae and report on those for 238 sp of mammals. Macrovibrissae are, so that you get an idea, the cat’s whiskers. Microvibrissae are much smaller. None of the great apes have macrovibrissae, in fact, they are the only mammals that lack them. In contrast, the author reports microvibrissae in all of great apes, 12 on average in gorillas, 22 in chimps and 59 in orangutans. My question is, are human beards and moustaches the functionally equivalent to microvibrissae? they are androgen-dependent (mainly found in males).

  19. Blackbird March 17, 2011 at 7:15 pm

    sorry, humans are mentioned to say they have no vibrissae of any kind, (together with the giant anteater).

  20. Rainer Braendlein March 20, 2011 at 2:17 pm


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  21. Orthologian March 31, 2011 at 10:35 pm

    Awesome post, and very good analysis of previous literature as well as the current study. Keep it up!!

  22. YetAnotherKevin April 18, 2011 at 11:06 pm

    OK, really late to the party, and not a biologist, but can someone explain that chart? If it were just one pair of bars, showing the number of genera with the two mating systems, I would understand. But I’m completely baffled. Like the first pair.. so there are 4 genera of monogamous and 15 genera of non-monogamous primates that… have penis length? As opposed to having _no_ length? I’m totally confuzzled.

  23. YetAnotherKevin April 18, 2011 at 11:07 pm

    Ah, never mind, clicked on the image / link and now it makes sense.

  24. Pingback: Finalists announced in the 3 quarks daily science writing prize « A Primate of Modern Aspect

  25. Rob July 7, 2011 at 12:55 am

    So Im just a normal guy who was curious about this… These ARE normal on us? I’v had em since before i ever had sex so i knew it wasnt something I caught but it still confuses me.

  26. Black Iris October 13, 2011 at 11:17 pm

    I’m not sure why you’re disagreeing with the article so strongly. The original article isn’t available in full, but the claim Nature magazine made was just that losing penile spines could have been part of humans becoming more monogamous. Penile spines are something that are associated with sperm competition. Sperm competition is strongest when females aren’t monogamous. The idea makes sense, although there are no guarantees.

    There are other clues about human genitalia that also point to the idea that human females were more monogamous than chimpanzees. So why all the fuss?

  27. Black Iris October 13, 2011 at 11:21 pm

    The bit about the church is just silly. Mating systems are just biology. Some primates are monogamous. Some have monogamous females sharing one guy. Some have females and males who are non-monogamous. There’s nothing religious about suggesting that humans fall into one of those those patterns.

  28. virgilio baylosis October 17, 2011 at 8:36 pm

    plenty of the biblically un educated catholics will surely condemn you for an article discussing in part a pope’s genetalia.but i say, bravo eric!! it is .a very enlightening piece and prove that a catholic spiritual leader after all is a human being..encore!!

  29. virgilio baylosis October 17, 2011 at 8:37 pm

    plenty of the biblically un educated catholics will surely condemn you for an article discussing in part a pope’s genitalia.but i say, bravo eric!! it is .a very enlightening piece and prove that a catholic spiritual leader after all is a human being..encore!!

  30. Michael McGrath December 19, 2011 at 2:33 am

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