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Bering in Mind


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Why do human testicles hang like that?


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Earlier this year, I wrote a column about evolutionary psychologist Gordon Gallup’s “semen displacement hypothesis,” a convincing hypothesis presenting a very plausible, empirically supported account of the evolution of the peculiarly shaped human penis. In short, Gallup and his colleagues argued that our species’ distinctive phallus, with its bulbous glans and flared coronal ridge, was sculpted by natural selection as a foreign sperm-removal device. As a companion piece to that work on our phallic origins, Gallup, along with Mary Finn and Becky Sammis, have put forth a related hypothesis in this month’s issue of Evolutionary Psychology. This new hypothesis, which the authors call “the activation hypothesis,” sets out to explain the natural origins of the only human body part arguably less attractive than the penis–the testicles.

In many respects, the activation hypothesis serves to elaborate what many of us already know about descended scrotal testicles: that they serve as a sort of “ cold storage” and production unit for sperm, which keep best at lower body temperatures. But it goes much further than this fact, too. It turns out that human testicles display some rather elaborate yet subtle temperature-regulating features that have gone largely unnoticed by doctors, researchers and laymen alike. The main tenet of the activation hypothesis is that the heat of a woman’s vagina radically jumpstarts sperm that have been hibernating in the cool, airy scrotal sack. Yet it explains many other things too, including why one testicle is usually slightly lower than the other, why the skin of the scrotum becomes more taut and the testicles retract during sexual arousal, and even why testicular injuries–compared to other types of bodily assault–are so excruciatingly painful to men.

The opening line of Gallup’s new article helps readers to appreciate the oddity of the scrotum:

 

It is almost unthinkable to ask why ovaries do not descend during embryological development and emerge outside the female’s body cavity in a thin, unprotected sack…

 

After you’ve finished exorcising that unsettling image from your mind, consider that the dangling gonads of many male animals (including humans) are no less puzzling. After all, why in all of evolution would nature have designed a body part with such obviously enormous reproductive importance to hang off the body so defenseless and vulnerable? Although we tend to become accustomed to our body parts and it often fails to occur to us to even ask why they are the way they are, some of the biggest evolutionary mysteries are also the most mundane aspects of our lives.

Thus, the first big question is why so many mammalian species evolved hanging scrotal testicles to begin with. The male gonads in some phylogenetic lineages went in completely different directions, evolutionary speaking. For example, modern elephants’ testicles remain undescended and are deeply embedded in the body cavity (a trait referred to as “testicond”), whereas other mammals, such as seals, have descended testicles but are ascrotal, with the gonads simply being subcutaneous.

Gallup and his coauthors jog through several possible theories of our species’ testicular evolution by descent. One of the more fanciful accounts–and one ultimately discarded by the authors–is that scrotal testicles evolved in the same spirit as peacock feathers. That is to say, given the enormous disadvantage of having your entire genetic potential contained in a thin satchel of unprotected, delicate flesh and swinging several millimeters away from the rest of your body, perhaps scrotal testicles evolved as a sort of ornamental display communicating the genetic quality of the male. In evolutionary biology, this type of adaptationist account appeals to the “handicapping principle.” The theoretical gist of the handicapping principle is that if the organism can thrive and survive while still being hobbled by such a costly, maladaptive trait such as elaborate, cumbersome plumage or (in this case) vulnerably drooping gonads, then it must have some high quality genes and be a valuable mate.

Although descended scrotal testicles do satisfy the obvious criterion of being counterintuitively costly, the authors conclude that handicapping is an unlikely explanation. If it were true, we would expect to see scrotal testicles becoming increasingly elaborate and dangly over the course of evolution, not to mention women should display a preference for males toting around the most ostentatious scrotal baggage. “With the possible exception of colored male scrota among a few species of primates,” write Gallup and his colleagues, “there is little evidence that this has been the case.” I’m not aware of any studies on intra-species individual variation in scrotal design, but I’m nonetheless willing to speculate that most human males have rather bland, run-of-the-mill scrota. Anything deviating from this–particularly a set of unusually pendulous testicles suspended in knee-length scrota–is probably more likely to have a woman dry-heaving, screaming, or staring in confusion than serving as an aphrodisiac.  

Again, a more likely explanation for scrotal descent, and one that has been around for some time, is that sperm production and storage is maximized at cooler temperatures. “Not only is the skin of the scrotal sack thin to promote heat dissipation,” the authors write:

 

…the arteries that supply blood to the scrotum are positioned adjacent to the veins taking blood away from the scrotum and function as an additional cooling/heating exchange mechanism. As a consequence of these adaptations average scrotal temperatures in humans are typically 2.5 to 3 degrees Celsius lower than body temperature (37 degrees Celsius), and spermatogenesis is most efficient at 34 degrees Celsius.

 

Sperm, it turns out, are extraordinarily sensitive to even minor fluctuations in room temperature. When the ambient temperature rises to body temperature levels, there is a temporary increase in sperm motility (that is to say, they become more lively), but only for a period of time before fizzing out. To be more exact, sperm thrive at body temperature for 50 minutes to four hours, the average length of time it takes for them to journey through the female reproductive tract and to fertilize the egg. But once the spermatic temperature rises much above 37 degrees Celsius, the chances for a successful insemination consequently plummet–any viable sperm become the equivalent of burnt toast. So in other words, except during sex, when it’s adaptive for sperm to be highly mobile and hyperactive, sperm are stored and produced most efficiently in the cool, breezy surroundings of the relaxed scrotal sack. One doesn’t want their scrotum to be too cold, however, since nature has calibrated these temperature points at precisely defined optimal levels.

Fortunately, human scrota don’t just hang there holding our testicles and brewing our sperm, they also “actively” employ some interesting thermoregulatory tactics to protect and promote males’ genetic interests. I place “actively” in scare quotes, of course, because although it would be rather odd to ascribe consciousness to human scrota, testicles do respond unintentionally to the reflexive actions of the cremasteric muscle. This muscle serves to retract the testicles so they are drawn up closer to the body when it gets too cold–just think cold shower–and also to relax them when it gets too hot. This up-and-down action happens on a moment-to-moment basis, thus male bodies continually optimize the gonadal climate for spermatogenesis and sperm storage. It’s also why it’s generally inadvisable for men to wear tight-fitting jeans or especially snug “tighty whities”–under these restrictive conditions the testicles are shoved up against the body and artificially warmed so that the cremasteric muscle cannot do its job properly. Another reason not to wear these things is that it’s no longer 1988.

Now, I know what you’re thinking. “But Dr. Bering, how do you account for the fact that testicles are rarely perfectly symmetrical in their positioning within the same scrotum?” In fact, the temperature regulating function governed by the cremasteric muscle can account even for the most lopsided, one-testicle-above-the-other, waffling asymmetries in testes positioning. According to a 2008 report in Medical Hypotheses by anatomist Stany Lobo from the Saba University School of Medicine, Netherlands Antilles, each testicle continuously migrates in its own orbit as a way of maximizing the available scrotal surface area that is subjected to heat dissipation and cooling. Like ambient heat generated by individual solar panels, when it comes to spermatic temperatures, the whole is greater than the sum of its parts. With a keen enough eye, presumably one could master the art of “ reading” testicle alignment, using the scrotum as a makeshift room thermometer . But that’s just me speculating.

From an evolutionary perspective–in contrast to my own personal perspective–the design of male genitalia only makes sense to the extent that it adaptively complements the female anatomy. In contrast to males, unless a woman is doing something unusual, the female reproductive tract is maintained continuously at standard body temperature. This is the crux of Gallup’s “activation hypothesis”: The rise in temperature surrounding sperm as occasioned by ejaculation into the vagina “activates” sperm, temporarily making them frenetic and therefore enabling them to acquire the necessary oomph to penetrate the cervix and to reach the fallopian tubes. “In our view,” write the authors:

 

…descended scrotal testicles evolved to both capitalize on this copulation/insemination contingent temperature enhancement and function to prevent premature activation of sperm by keeping testicular temperatures below the critical value set by body temperatures.

 

One of the things you may have noticed in your own genitalia or those of someone you’re especially close to is that, in contrast to the slackened scrotal skin accompanying flaccid, non-aroused states, penile erections are usually accompanied by a telltale retraction of the testicles closer to the body. This is the sort of thing easiest to demonstrate using visual illustrations–the editors at Scientific American wouldn’t let me get away with it here, but a quick Google image search should provide ample examples. Just choose your own search terms and disable “safe search”–though if you’re at work right now, you may want to save this as homework for later. According to Gallup and his coauthors, this is another smart scrotal adaptation. Not only does the cremasteric reflex serve to raise testicular temperature, thus mobilizing sperm for pending ejaculation into the vagina, but (added bonus) it also offers protection against possible damage to too-loose testicles resulting from vigorous thrusting during intercourse.

There are many other ancillary hypotheses connected to the activation hypothesis as well. For example, the authors ponder whether humans’ well-documented preference–and one rather unique in the animal kingdom–for nighttime sex can be at least partially explained by temperature-sensitive testicles. Although the authors note the many benefits of nocturnal copulation (such as accommodating clandestine sex or minimizing the threat of predation), this preference may also reflect a circadian adaptation related to descended scrota. Given that our species evolved originally in equatorial regions where daytime temperatures often soared above body temperature, optimal testicular adjustments would be difficult to maintain in such excessive heat. In contrast, ambient temperatures during the evening and at night fall below body temperature, returning to ideal thermoregulatory conditions for the testes. Additionally, after nighttime sex the woman is likely to sleep, thus remaining in a stationary, often supine position that also maximizes the odds of fertilization.

Although the activation hypothesis helps us to better understand the functional, if quirky, architecture of the human male gonads, it may still seem odd to you that nature would have invested so heavily in such a precipitously placed genetic bank. After all, we’re still left with the curious fact that our precious gametes are literally hanging in the balance in a completely unprotected vessel. Gallup and his coauthors aren’t unaware of this strange biological fact either:

 

Any account of descended scrotal testicles must also address the enormous potential costs of having the testicles located outside the body cavity where they are left virtually unprotected and especially vulnerable to insult and damage. To be consistent with evolutionary theory the potential costs of scrotal testicles would have to be offset not only by compensating benefits (e.g., sperm activation upon insemination), but one would also expect to find corresponding adaptations that function to minimize or negate these costs.

 

Enter pain. Not just any pain, but the unusually acute, excruciating pain accompanying testicular injury. Most males have some horrific stories to tell on this score–whether it be a soccer ball to the groin or the flailing foot of a sibling–but each of us men shares something in common: we’ve all become extraordinarily hypervigilant against threats to the welfare of our scrotal testicles. The fact that males are so squeamish and sensitive to this particular body part, point out the authors, can again be understood in the context of evolutionary biology. If you’re male, the reason that you probably wince when you hear the word “squash” or “rupture” paired with “testicle” but not with, say, “arm” or “spleen” is because testicles are disproportionately more vital to your reproductive success than these other body parts are. I, for one, had to pause to cover myself just by typing those former words together. It’s not that those other body parts aren’t adaptively important, but variation in pain sensitivity across different bodily regions, according to this view, reflects the vulnerability and importance different adaptations play in your reproductive success. Male ancestors who learned to protect their gonads would have left more descendants–and pain is a pretty good motivator for promoting preemptive defensive action. Or, to think about it another way, any male in the ancestral past that was oblivious to or, gulp, enjoyed testicular insult would have been quickly weeded out of the gene pool.

Additionally, argues Gallup, the cremasteric muscle flexes in response to threatening stimuli, in effect pulling the testicles up closer to the body and out of harm’s way. In fact, the authors point out, Japanese physicians have been known to apply a pin prick to the inner thigh of male patients as a surgical prep: if the patient displays no cremasteric reflex, this means the spinal anesthesia has kicked in and he’s ready to go under the knife. Other evidence suggests that fear and the threat of danger trigger the cremasteric reflex. I suspect there are any number of ways to test this at home, if you’re so inclined. Just make sure the owner of the fearfully reflexive testicles knows what you’re up to before frightening him.

So, there you have it. A new, evolutionarily informed account of the natural origins of descended scrotal testicles in humans. What do you think of Gallup’s seminal theory? Is the whole thing nuts? Don’t leave me hanging, folks. Ball’s in your court. ba dum ching!

 

In this column presented by Scientific American Mind magazine, research psychologist Jesse Bering of Queen’s University Belfast ponders some of the more obscure aspects of everyday human behavior. Ever wonder why yawning is contagious, why we point with our index fingers instead of our thumbs or whether being breastfed as an infant influences your sexual preferences as an adult? Get a closer look at the latest data as “Bering in Mind” tackles these and other quirky questions about human nature. Sign up for the RSS feed or friend Dr. Bering on Facebook and never miss an installment again. For articles published prior to September 29, 2009, click here: older Bering in Mind columns.

Image ©iStockphoto.com/Alija





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  1. 1. Fausty 6:54 pm 11/19/2009

    This analysis would be more compelling if it took into account the parallels in other mammalian males. Stallions also "retract" their testicles immediately prior to ejaculation – but there’s not much chance it’s driven by thermoregulation as, frankly, things happen too fast in equines for temperature changes.

    In contrast, dogs don’t retract their testicles during ejaculation. Then again, dogs ejaculate for 20+ minutes so it’s a tough comparison. Still, if thermoregulation mattered, dogs would be the ideal species to retract and up the temperature during the canine "tie" that accompanies mating. No such thing takes place.

    These studies that treat human beings as if they were placed on the planet by aliens – utterly separate from the "animals" who share our world and genetic heritage – are a throwback to sloppy science 50 years old. It takes not so much effort to actually dig into comparable species’ data, which is easy to locate and review nowadays. Why, then, are we left with the sense that there’s almost a religious hesitation to compare humans to "animals?"

    Oh, that’s right, because there IS a religious hesitation that drives this whole silly delusion. Too bad it still holds sway in legitimate scientific research.

    Fausty | http://www.zetawisdom.net

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  2. 2. robynmcintyre 7:14 pm 11/19/2009

    I like a man who can talk science and be funny at the same time. Reading temperature by evaluating a scrotum… what a picture!

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  3. 3. miss_emelia 7:17 pm 11/19/2009

    Mr. Bering, you’re my hero. "not 1988." It’s a rare thing to find myself laughing while reading science news, but you do the most remarkable job of balancing facts and humor in a positively Whedonesque way.

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  4. 4. Fausty 7:27 pm 11/19/2009

    To be fair, I echo the appreciation of good science writing and good humor – should have included that in my earlier comment. My criticism of the *underlying* research takes nothing away from Dr. Bering’s exquisite writing on this – and related – subjects. Hats off to quality writing from a whip-smart mind.

    Fausty | http://www.zetawisdom.net

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  5. 5. svshepherd 7:42 pm 11/19/2009

    i continue to be amused by the hypothesis (i forget the journal where i encountered it) that external scrota evolved to avoid intraperonital pressure fluctuations that accompany running/leaping. the idea was that males have external scrota to prevent them from leaking semen whenever they move too vigorously.

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  6. 6. Dolmance 12:49 am 11/20/2009

    Dog’s testicles hang too. I believe it’s a case of natural selection, because women seem to quite enjoy them. At least mine does.

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  7. 7. Moodie-1 2:16 am 11/20/2009

    "How do you account for the fact that testicles are rarely perfectly symmetrical in their positioning within the same scrotum?" Well, after reading "Sperm, it turns out, are extraordinarily sensitive to even minor fluctuations in room temperature." in your article it occurred to me that maybe they’re even more thermally sensitive than most experts think. Consider this possible scenario: when the ambient air temperature falls the scrotum is drawn up close to the body until the uppermost testicle starts to get too warm, then all movement stops. This would ensure that the lowermost testicle is kept in the comfortable range. It works the opposite way too. When the ambient air temperature rises the scrotum is allowed to hang lower until the lowermost testicle starts to get too cool. The uppermost testicle would then be in the comfortable range. Either way in most circumstances there would always be at least one reliable testicle.

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  8. 8. old dingo 7:18 am 11/20/2009

    I am amazed if nobody else has seen this. To me the obvious hypothesis to explore is that having temperature-sensitive germ cells, and cells that mature at a lower temperature than body temperature is likely to be a protection against viral infection of those cells.

    Yep, the first thing to do when subject to a viral infection, particularly one that might end up integrated in your valuable DNA is that you wipe out your sperm reservoir and start again. For us, who invest a huge k (ie number of resources in our offspring), wasting the reproductive chance and several decades of looking after a damaged child is a huge cost, nearly equivalent to being castrated. This ties in nicely with the fever response associated with viral infection. I suspect that a bit of molecular "archeology" in our genome might turn up the remains of a retrovirus around about the time that this sperm thermal sensitivity arose.

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  9. 9. mapmanic 12:01 pm 11/20/2009

    I used to work at a food processing plant where large blades were employed to slice garlic and onions. When walking past the knife sharpening shop, invariably and involuntarily, I could feel my scrotum "suck up." This happened even if I were not consciously thinking "I’m near the knife shop" but my scrotum would remind me of the fact.

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  10. 10. rb3000 1:04 pm 11/20/2009

    I was squirming in my chair the whole time reading this article and became hyper-aware of my sack, am I alone in this?

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  11. 11. rb3000 1:06 pm 11/20/2009

    I was squirming in my chair the whole time reading this article and became hyper-aware of my sack, am I alone in this?

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  12. 12. Albert Reingewirtz 1:43 pm 11/20/2009

    An evolutionary psychologist discusses body parts? Remember psychologists getting clients up the kazoo with their explanation of the cause of ulcers? There is more interesting feature of human male sex organs, the prostate. Every male if he is lucky to reach maturity will wonder because of this organ’s restrictive capacity to urinate. He will have plenty of time many times a day … and nights about "Intelligent Design." Like me they will repeat endlessly this is nuts!

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  13. 13. Fausty 5:32 pm 11/20/2009

    Err, I’d think it fairly obvious that my criticism of lack of cross-species comparison was specific to the "cremaster response" and not to the question of testicle location in general. That’d be why I used as counter-examples specific instances where the cremaster response didn’t meet the model’s predictions as proposed by Dr. Bering.

    Cherry-picking a few examples, even for the question of testicular location, in a cross-species survey doesn’t really do much to "prove" anything, in the event. That’s just an example of confirmation bias; the usefulness of cross-species stuff is, generally, to *disconfirm* via examples that fail to match the predictions of a human-centric theory. Smart researchers, like Dr. Bering, certainly understand this and his use of a few examples from other species is certainly intended here as an expository device, not meant to "prove" any specific theory.

    Alas, not every reader is so smart – hence the need to explain basic logical concepts occasionally. I could propose a correlation between that lack of logical competence, and mystico-religious, magical belief systems… but that’d just be too easy.

    Once again, kudos to Dr. Bering for the willingness to tackle this – and related – subjects in a public, sharp-elbowed space like this. It’s trivially easy for research scientists, nowadays, to hide themselves from any criticism from outside their sub-sub-branch of academia, if they so choose. The truly creative thinkers rarely take that coward’s route, however.

    Fausty | http://www.zetawisdom.net

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  14. 14. solidreign 7:46 pm 11/20/2009

    This is a discussion on genetalia, so I feel free to use some choice words.

    Firstly, I confirm that this article is the dog’s bollocks.

    Lastly, being right does not give you free reign to be a prick, but alas, not every dick notices when his head is swollen. You might have better luck getting people to touch your massive raging knowledge if you don’t swing your testicles in their face on the first date.

    And post-lastly, I also became hyperaware of my sack. You are not alone, rb3000, unless you’re a malicious robot talking about the sack of batteries you carry around to cull the human herd?

    If so, then, yeah, you might be alone on that.

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  15. 15. jack.123 8:58 pm 11/20/2009

    If you will pardon the language, but this reminds of joke a doctor told me.A man went to visit his friend at an insane asylum,when arriving at his room, he found him on his back with a large erection with a peanut on the end of it, when asking what the hell he was doing ,he responded I am f—ing nuts can’t you see that. What if all diagnosis and science could be that simple.

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  16. 16. NietzscheLovesMommy 12:29 am 11/21/2009

    Argument for Intelligent Design # 340,560,987”

    Thank you

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  17. 17. alanb 1:06 pm 11/21/2009

    This explanation leaves me (at least several degrees) cold(er).

    Wouldn’t it have made more evolutionary sense to "keep the orchid in the crypt," and develop sperm that was less heat sensitive?

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  18. 18. glennnn 5:16 pm 11/21/2009

    " Reading temperature by evaluating a scrotum… what a picture!"
    Anyone else remember the joke about telling the time by feeling donkey balls?

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  19. 19. kyle9830 5:43 pm 11/22/2009

    Do men who have their testicles replaced with prosthetic balls have the thermo retraction response?

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  20. 20. will.judith@prodigy.net 8:55 pm 11/22/2009

    Note that hanging testicles greatly facilitate castration with little threat to the victim’s survival. I can imagine that castration of subordinate males might have survival value for the tribe/species that practices it. Besides taking inferior genes out of the tribal pool, it supplies the tribe with relatively docile workers. This could also explain mapmanic’s instinctive fear of castration.

    I’ve noticed that these discussions of evolutionary biology tend to avoid injury and violence. Here’s another example: When a male is strangled, he ejaculates as he nears death. It’s hard to imagine that this reflex is accidental. So consider the case when a woman’s husband and/or male relatives catch an intruder in the act and strangle him. This raises the question whether any other mammals practice castration. Also, there are rare reports of women having involuntary penis captivus. If true, this would support the strangulation scenario as opposed to some other form of attack against the intruder.

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  21. 21. Will9194 2:36 am 11/23/2009

    Note that hanging testicles are especially convenient for castration with minimal risk to the victim. Perhaps a tribe or species gains some survival advantage by castrating its subordinate males. This not only takes inferior genes out of the tribal gene pool, but it also provides relatively docile workers. This would explain mapmanic’s instinctive fear. It also raises the question, does any other mammal with hanging
    testicles also practice castration, presumably by biting the testes?

    I’ve noticed that these discussions of sociobiology tend to avoid
    explanations with violence or injury. For another example, consider that a man being strangled ejaculates as he dies. Seems unlikely that this is an accidental side effect. But suppose a woman’s husband and/or male relatives catch an intruder in the act and strangle him. Now ejaculation starts to make sense, except we must explain why the they don’t pull the couple apart first. There are rare reports of women having involuntary penis captivus. If this were common in ancient times, it would complete the explanation.

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  22. 22. Will9194 2:39 am 11/23/2009

    Note that hanging testicles are especially convenient for castration with minimal risk to the victim. Perhaps a tribe or species gains some survival advantage by castrating its subordinate males. This not only takes inferior genes out of the tribal gene pool, but it also provides relatively docile workers. This would explain mapmanic’s instinctive fear. It also raises the question, does any other mammal with hanging
    testicles also practice castration, presumably by biting the testes?

    I’ve noticed that these discussions of sociobiology tend to avoid
    explanations with violence or injury. For another example, consider that a man being strangled ejaculates as he dies. Seems unlikely that this is an accidental side effect. But suppose a woman’s husband and/or male relatives catch an intruder in the act and strangle him. Now ejaculation starts to make sense, except we must explain why the they don’t pull the couple apart first. There are rare reports of women having involuntary penis captivus. If this were common in ancient times, it would complete the explanation.

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  23. 23. ellenmmartin 11:51 am 11/23/2009

    So, how do elephants mange the thermoregulation of sperm?

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  24. 24. inno 2:44 pm 11/23/2009

    Interesting idea, but the ease of castration cannot possibly explain the scrotum – otherwise castration would either have to be a prevalent practice in all species with this feature, or they would have to have a common ancestor that practiced it.

    Also, I would even dispute the idea that castration of less powerful males can confer an evolutionary advantage – suppose that something happens in a group of animals that renders the one, or sevaral uncastrated males unable to mate – certainly coninuation of the line, even fostered by slightly inferior specimens, is preferred to the dying out of the entire group.

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  25. 25. cygnus 8:11 am 11/24/2009

    moodie,
    for your last sentence, you said "When the ambient air temperature rises the scrotum is allowed to hang lower until the lowermost testicle starts to get too cool. The uppermost testicle would then be in the comfortable range. Either way in most circumstances there would always be at least one reliable testicle."
    but the other side of the coin is "there will always be one testis in the wrong temperature", it seems to be a waste to do so when the body is fully capable in choosing and detecting the right temperature for such an important organ

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  26. 26. jparkes1 1:45 am 11/25/2009

    My opinion would be a combination of factors involved in the evolution of both the scrotum and the sperm cell. Biologically the theory of potential viral damage and the fragility of motility/temperature, and the genetic content of sperm cells had to have become an evolutionary compromise.
    It seems miraculous in the extreme that they function at all, but it seems the numbers and the trial of the fittest sperm cells allow the species to rise above the least healthy of the sperm.
    Nature/evolution is genius in it’s use of a built in safeguard (only in as far as it goes) ensuring only the fittest to claim an egg. Though unexplained still is the presence of genetic abnormalities accredited to defaults in the successful sperm cell. Perhaps that is a remnant of past viral success, or environmental exposures of the donor. I’m inclined to believe that evolution is still working on this and has yet to find that compromise/solution.
    According to my societal values I find the need for the castration of abnormal males to be more and more a viable alternative to well intentioned, but ineffective, psychological treatment of behaviorally unacceptable male abnormalities.
    Even my admission of that terrifies me in an instinctive way. I still stand by that statement though, as the alternatives have failed in a most consistent way.
    Culturally speaking my three daughters find the testicles of our three male dogs not at all odd or repulsive. In fact it’s never been a topic of discussion, though that may negate my understanding of their acceptance and may be unrelated to potential human mates.
    Evolution is in no way perfect or finished. We are always in the midst of change, some will lead to advances and others will not, it scares me to know all the people I love are test subjects to a phenomenon that answers to no man(or woman).
    I feel we need a more intensive study of our past, particularly on a micro level to gain some small measure of what evolution has in store for our species in the future.
    That’s my two cents worth as an interested layman, I’m an engineer by trade with an unhealthy interest in things I know very little about.

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  27. 27. jparkes1 2:06 am 11/25/2009

    Fausty, I recognize the Frustration with religion when it interferes with the thinking and formulation of strictly scientific research.
    I think personal values have no place in fact finding research as it is not a morality concern when verifying 1+1=2. Because ‘god made it that way’ does not provide verifiable proof that this is so.
    Much like psychological evaluation, religion is a set of beliefs founded on faith and neither are hard science, but are still of value in many ways to the human state.
    A religious person may do well in science, but they must find a way to separate personal belief and the search for verifiable facts.
    You were the target of a clearly biased person of faith who has let themselves blur the lines in factual research and scientific fact finding, and I feel that was unfair. Admittedly I have minimal exposure to your posts so you may be fanatic in your anti religious views, I don’t know, or need to.

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  28. 28. SuperJesus 12:51 pm 11/25/2009

    "Ostentatious Scrotal Baggage" would make a great name for a band.

    Super J

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  29. 29. ecoligist 10:38 pm 11/25/2009

    It might interest you that elephants and larger mammals tend to have lower normal body temperatures. Elephants are about 35c, so bull elephants don’t need a "room" with a view. And dogs, by the way, have normal temperatures higher than those of Homo sapiens. Then there are sloths with body temps at about 30c. How do their sperm get motivated?

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  30. 30. retired01 2:37 pm 11/26/2009

    Mania that passes for religion does not merit comment.
    But for those who wonder about religious references, the sanctity and vulnerability of the testes are noted in Genesis 24:2, 47:29 (somewhat explicit) and Deuteronomy 25:11 (quite explicit)

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  31. 31. retired01 2:41 pm 11/26/2009

    Mania that passes for religion does not merit comment.
    But for Biblical references to the sanctity and vulnerability of testes see Genesis 24:2, 47:29 (somewhat explicit) and Deuteronomy 25:11 (quite explicit).

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  32. 32. Duzzle 3:51 pm 11/26/2009

    "It is almost unthinkable to ask why ovaries do not descend during embryological development and emerge outside the females body cavity in a thin, unprotected sack&"

    Oh, if only it were that easy to be rid of the damn things.

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  33. 33. leonretief 5:31 pm 11/26/2009

    An interesting hypothesis, but I see a small problem. We read: " The main tenet of the activation hypothesis is that the heat of a woman’s vagina radically jumpstarts sperm that have been hibernating in the cool, airy scrotal sack. " Sperm do not hibernate in the cool scrotum after being produced, it goes to the seminal vesicles, right inside the abdominal cavity, and is stored there, at body temperature, until ejaculation.
    Leon

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  34. 34. pradhangeorge 7:25 am 11/28/2009

    the beauty of science lays in the for and against it kicks up. gallup’s findings and bering’s fun make the brain think deep.=== here be some from my doubts : # my anatomy prof. 1945 said that the quadrupeds had the hanging balls one in front of the other too.#The sperm are born in the semeniferous tubes and stay in the epddmis some time to grow up,# how hibernating or brewing?…and by dartos’ [stuck muscle under the blacker rugaed skin] movements rolling the balls squeezed out and up the tubes vasa, to the deep down in the hot pelvis seminal vesicles where they get the juice,and stay there for a whole day ,deep afore the rectum where the temperature is 0.5*C higher than the mouth 37*C. # Sun down encourages sex activity in both, due to the circadian, bio-clock, mind, environ, society, hormonal, pituitary, rhythms, # and as soon as the coital reflexes empty the vesicles , the sex urge drops often instantly, and until the next fill up of the vesicles.# Why at all did the gonads of both sexes migrate down from next to the Kidneys totally out in the males and partly into the pelvis in the femme, gubernaculum notwithstanding? # an erect penis of a magnetic male is the most perfect sight for a woman in heat.#The pain of Torsion testes is worse than a kidney stone. or an injury.# it was nice i chanced upon this SciAm letter…………A pity i cant afford a paid membership.

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  35. 35. Fausty 5:21 pm 11/30/2009

    I’d say that "The Sanctity of the Testes" is another near-perfect band name… ;-)

    Fausty | zetawisdom.net

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  36. 36. dudeinhammock 6:47 am 12/2/2009

    Interesting, but the business about sex at night being protection from predators is bass-ackwards. Most predators hunt at night, not during the day. If predator avoidance were the issue, a mammal like humans, with very weak night vision, would be having sex in the mid-day sun, not in darkness.

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  37. 37. grazingkow 11:07 pm 12/3/2009

    Brilliant article extremely interesting.
    Kudos.

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  38. 38. grazingkow 11:08 pm 12/3/2009

    Brilliant Article. Very Interesting stuff.
    Kudos.

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  39. 39. fires 2:26 am 12/10/2009

    So, why does my scrotum remain tight against my body about 95% of the time? Not kidding. Any serious explanation(s)? I’ve never gotten one from any doctor.

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  40. 40. Didonai 3:20 am 06/25/2011

    Other theories are laudable but I tend to believe human testicles that move rhythmically during the dangle do so as a trance forming conduct purposed to make females more amenable to the sex act. Dancing testicles perform a kind of cultural horn dance between the hairy male pillars in celebration of necessary coital entanglements common to all social animals with ambition for species longevity via procreation. Doubters may go argue with anthropologists and sociologists…who are quite willing to argue and are PAID to argue about the things that are important enough to pay for. Really?
    Yes. Dancing testicles that engage females in hypnotic stupor. Its so logical I don’t know why there isn’t a doctorial dissertation somewhere focused on the throbbing sack of man.

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