Why do human testicles hang like that?
scientificamerican.com
scientificamerican.com
With evolution, there's no "why", unless you count "it was evolutionarily beneficial, so it was selected for". But even that doesn't explain everything, like genetic drift.
From Wikipedia: Teleology (Greek: telos: end, purpose) is the philosophical study of design and purpose.
What happens is that ideas are often conveyed using teliological phrases, such as
"the sparrows migrate to africa in the winter month so as to find abundant food sources and rear the next generation..." or "testicles reside outside of the body major in order to benefit from a reduced temperature...".
The problem is that these make sense to us, although they are _very_ incorrect. The teleological concepts of "so as" or "in order to" are the whys and they are very tricky beasts. So, for utmost correctness one would prefer to say:
"the sparrows migrate to africa in the winter month finding the abundant food sources needed to rear the next generation..." or "testicles reside outside of the body major benefitting from a reduced temperature..."
It's a very subtle issue, and one that is compounded by the popularity and ease with which we talk about biology and evolution in particular. Ernst Mayr wrote some spectacular essays on the subject, he's one of my heros so forgive me for the blatent plug! He claims that a formal understanding of the errors of telology must permeate the sciences, and most especially biology (he was a philosopher of biology), so as to clear up the ambiguities that can lead one to think there is an end or purpos (telos) to evolution. Even now it is still quite common for people to think of it in terms of progress and constant betterment instead of just simple and blind adaptation.
Another reason that people may react harshly when you use teleological language is that biology (unlike physics) is constantly under attack by people with all sorts of crazy theories about a supernatural designer - (talk about a teleology!) so I can understand why such language would be somewhat taboo.
Another reason might be that maintaining the testicles at body temperature increases the risk of infection. There are very few purely sexually transmitted diseases, likely due to this temperature difference. Those same sexually transmitted diseases rarely cause harm beyond the genitals, and in fact these diseases are far more harmful to the female reproductive system than the male (a woman with undiagnosed gonorrhoea or chlamydia is essentially guaranteed to become sterile, however in men it either takes longer, or they may never become sterile - note that a male can lose a testicle to injury or disease without becoming sterile or losing fertility).
It's likely that there were more advantages to any male with dangling gonads over retracted. The reason why our testicles require constant temperature control (and independent control) is probably a more intriguing question, which IMO likely has a lot to do with our method of motility. A dog's testicles are unlikely to be affronted by the sun, however any naked male human has a serious problem when walking toward the sun. This likely wasn't a problem when we were semi-erect (in the evolutionary sense, not the other sense) and had hairy gonads, however why did modern humans develop wholly unprotected gonads? Think about it, our testicles don't even have protection against the sun! Dense hair provides protection against heat stroke, so did humans already have protection for our genitals before this became a problem? IE did our invention of clothing happen early enough that it actually changed the development of our sexual organs?
From what I know about biology/evolution, this answer is just as likely to have a single clean reason as it is that you killed the one and only cockroach living in your apartment.
(nature tends to work this way; it's essentially a hack right)
One thing the article did get me wondering, and if any hacker here has gone through this and be willing to admit it, i'd love to know:
If you have to ask a doctor for help get pregnant... i.e. if your little fella isn't up to the job- i wonder if there's a course of therapeutic treatment simply around better managing the temperature of the scrotum? I'd imagine it'd be hanging around in loose fitting shorts in a temperature controlled setting until such time as your partner would be ovulating? :)
With ~4 million sperm cells per... egg, there is enormous selective pressure that gets exerted by competition among individual spermatozoa. So the sperm cells that are the most temperature-sensitive (hence best able to take advantage of the metabolic boost due to increased ambient temperature, hence on balance faster-moving) would be heavily favored.
I feel like there needs to be a Your Mom joke in here somewhere...
The sperm are all produced by the same individual, and so you might expect them to be essentially identical aside from the genes they carry, in which case there's no Darwinian selection between them.
However, if genes in the sperm are actually expressed (which would be normal for most other cells) then due to the process of meiosis, different sperm will have different genes and so selection between sperm from the same man could indeed occur.
Sadly I don't know the details of gene expression in sperm... the question really is whether they get their proteins from the parent cells (all of which are genetically identical to the man) or whether they make some of their own proteins.
Ah, I see from Google that there is indeed some gene expression in sperm: http://8e.devbio.com/article.php?ch=19&id=193
(In any case, there could of course be selection at the level of individual human males, with those producing better sperm having higher reproductive success.)
Longer but rambling explanation: http://www.passengerplanet.com/softwarm.html
> 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.
" 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.' "
Clearly this refers to us chaps having scrota that we could either puff up like a balloon or flatten out to wave around like a fan, or even change color (like so many of the mating displays of the wild). However, the author fails to recall the time of Shakespeare (and, in some cultures, still today), in which men would wear a codpiece to promote their wares:
http://en.wikipedia.org/wiki/Codpiece
(interestingly, Codpiece is from the middle english 'cod' which means, scrotum)
I bring this up not to be pedantic, but because it's important to say what we mean. In this instance, the author's language suggests he isn't aware of the codpiece and, well, for scientific american - this feels like poor journalism. Better to say what you actually meant, if writing for the sake of oratory confuses the intent.
Not the kind of skill you'd want to brag about -- assuming you are a heterosexual male, that is.
Thank you.
It was an odd quote, and didn't fit in with the rest of the article (which I thought was very good, btw) Plus it set off all sorts of sophomoric jokes at least in my mind.
It didn't fit. It was appropriate to point it out -- even in a slightly humorous fashion. A smiley might have helped, but who knows? Like you said, it's all good.
My point: I tend to get in trouble over stuff like that in part because I'm not a homophobe and not judgmental, so it tends to not occur to me to that cracking such a joke would be (perceived as) a hostile act. And I think the underlying hostility behind so many "jokes" is why people are sensitive to things like that. But I will make a mental note that this forum is apparently not where it initially appeared to me in that regard and tread more lightly.
Thank you for the feedback. As an aside, I don't understand why requests for such feedback get downvoted in this forum. Punishing someone for doing something, then punishing them for asking "What did I do wrong?" and not explaining is an extremely poor de facto policy for helping people behave better and tends to have a chilling effect on conversation.
In other news:
"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."
This might be a neat party trick at a nudist camp, but I imagine it would tend to scream "fag" if you are male or "tramp" if you are female. As a WAG: Not likely to catch on.