# Flaccid-to-erect penises (almost) unique in humans?
**URL:** https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205
**Category:** Factual Questions
**Created:** [December 31, 2009, 6:13pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205 "2009-12-31T18:13:33Z")
**Posts on this page:** 15
**Page:** 2
### Author:  [@Jervoise](https://boards.straightdope.com/u/Jervoise)
#### Post date: [January 3, 2010, 4:56pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/21 "2010-01-03T16:56:29Z")
> [@EdwardLost](#):
>
> I wonder about the evolutionary benefit of humping the female for several minutes or more before delivering the seed. Wouldn’t it be advantageous to shoot in the first five seconds? You could still have the pleasure orgasm later for the pair-bonding.
> [@Der\_Trihs](#):
>
> I’d think that it’s because for humans the majority of sex is for the sake of relationships and pleasure. We even have a low fertility rate and a hidden fertile period for women; we have evolved for not only long, drawn out sex, but for having lots of sex when we aren’t even fertile. And another reason we have long drawn out sex is due to the exercise of self control, not to mention manual stimulation, toys, cunnilingus - all sorts of ways we’ve devised to get around the “built in” limits.
The action of thrusting also has the purpose of drawing out and displacing the semen of rivals that may already be present in the vagina. See: [http://www.epjournal.net/filestore/ep021223.pdf](http://www.epjournal.net/filestore/ep021223.pdf) (PDF)
Rather disturbingly:
> [@](#):
>
> Under conditions that raise the possibility of females engaging in extra-pair copulations (i.e., periods of separation from their partner, allegations of female infidelity), Gallup et al. (2003) also found that males appear to modify the use of their penis in ways that are consistent with the displacement hypothesis. Based on anonymous surveys of over 600 college students, many sexually active males and females reported deeper and more vigorous thrusting when in-pair sex occurred under conditions related to an increased likelihood of female infidelity.
So in a nutshell (so to speak), a man may require several minutes of sex in order to displace of spunk of other men who may have come (again, so to speak) before him. Isn’t sex SO romantic?
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### Author:  [@Mean\_Mr.Mustard](https://boards.straightdope.com/u/Mean_Mr.Mustard)
#### Post date: [January 3, 2010, 5:14pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/22 "2010-01-03T17:14:33Z")
> [@](#):
>
> There’s been much ado lately about the duck… It has a corkscrew penis
That could come in handy on New Years Eve.
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### Author:  [@WhyWhyWhy](https://boards.straightdope.com/u/WhyWhyWhy)
#### Post date: [January 3, 2010, 7:59pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/23 "2010-01-03T19:59:14Z")
And I’m thinking a bone would be so much cheaper than Viagra.
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### Author:  [@CC](https://boards.straightdope.com/u/CC)
#### Post date: [January 4, 2010, 3:20am UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/24 "2010-01-04T03:20:38Z")
Regarding the assumptions built into the OP: even some fish have to get it up. Watch some guppies for a while, or other live-bearers. The male comes up from underneath and to the side of the female and when he’s ready to have at her, he makes a small burst of speed for her while at the same time, his gonopodium (the dick, in technical terms) swings forward to be capable of entering her from her rear. That’s a fishie woodie. He doesn’t always holster it in the forward position. Something makes it go like that. Boy fish like girl fish and it shows.
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### Author:  [@Quercus](https://boards.straightdope.com/u/Quercus)
#### Post date: [January 4, 2010, 2:07pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/25 "2010-01-04T14:07:44Z")
Right, the duck:
[http://blogs.discovermagazine.com/loom/2009/12/22/kinkiness-beyond-kinky/](http://blogs.discovermagazine.com/loom/2009/12/22/kinkiness-beyond-kinky/).
The relevant thing, for the OP, is that the duck has an erectable penis, though it’s lymph fluid, not blood that engorges it, and it engorges almost-explosively. But definitely flaccid \> erect.
So it’s not just humans, apes, or even mammals. Must be something worthwhile about erections, evolutionarily speaking.
Re: length of sex. I assume that part of the (evolutionary) purpose of mating rituals is to make sure that an actual mating with an appropriate partner is taking place. So an organism wants mating to take at least a little while, just to make sure it’s not a momentary false alarm.
In other words, if a couple seconds of stimulation was enough for a male orgasm, how often would a human male have to change his underwear?
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### Author:  [@aceplace57](https://boards.straightdope.com/u/aceplace57)
#### Post date: [January 4, 2010, 2:26pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/26 "2010-01-04T14:26:32Z")
Pigs are corkscrews too.
Thankfully Cecil looked so I wouldn’t have too. 😉
> **[Does a pig have a corkscrew-shaped penis?](https://www.straightdope.com/21341237/does-a-pig-have-a-corkscrew-shaped-penis)**
TMI
> [@](#):
>
> Much remains to be learned about pig reproductive physiology. For instance, it’s unclear whether the male pig, in the midst of his amatory labors, employs a clockwise or a counterclockwise rotation.
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### Author:  [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)
#### Post date: [January 4, 2010, 5:15pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/27 "2010-01-04T17:15:42Z")
Anteaters (the real ones, not the euphemism for uncircumcised human males) have four penises, two which ejacualate at a time. You can google it, also on utube where u can see the damn things, if you want. I’m not sure that would be a good or bad thing for humans…
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### Author:  [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)
#### Post date: [January 4, 2010, 5:34pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/28 "2010-01-04T17:34:04Z")
In ducks, the male corkscrew is matched–unfortunately for most, but evolutionarily fortunate for those lucky few–by _counter_ corkscrews in the female.
From the NYTimes, 4/30/2007 [full article has cites]:
Female ducks seem to be equipped to block the sperm of unwanted males. Their lower oviduct is spiraled like the male phallus, for example, but it turns in the opposite direction. Dr. Brennan suspects that the female ducks can force sperm into one of the pockets and then expel it. “It only makes sense as a barrier,” she said.
To support her argument, Dr. Brennan notes studies on some species that have found that forced matings make up about a third of all matings. Yet only 3 percent of the offspring are the result of forced matings. “To me, it means these females are successful with this strategy,” she said.
Dr. Brennan suspects that when the females of a species evolved better defenses, they drove the evolution of male phalluses. “The males have to step up to produce a longer or more flexible phallus,” she said.Female ducks seem to be equipped to block the sperm of unwanted males. Their lower oviduct is spiraled like the male phallus, for example, but it turns in the opposite direction. Dr. Brennan suspects that the female ducks can force sperm into one of the pockets and then expel it. “It only makes sense as a barrier,” she said.
To support her argument, Dr. Brennan notes studies on some species that have found that forced matings make up about a third of all matings. Yet only 3 percent of the offspring are the result of forced matings. “To me, it means these females are successful with this strategy,” she said.
Dr. Brennan suspects that when the females of a species evolved better defenses, they drove the evolution of male phalluses. “The males have to step up to produce a longer or more flexible phallus,” she said.
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### Author:  [@md2000](https://boards.straightdope.com/u/md2000)
#### Post date: [January 4, 2010, 6:02pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/29 "2010-01-04T18:02:16Z")
I suppose one evolution advantage for erections is selection - if the male is not interested, less likely to reproduce. Also, if the male is stressed or unhealthy, it means he is less likely to reproduce.
As for why we enjoy sex - there’s a whole long discussion in science on why thatis; women hide fertile times (even from themselves) because it means they were more likely to receive “food offerings” all the time from interested “suitors”. If men knew the right time, they would not be as interested other times. To ensure we do it early and often sinc we don’t know when, sex is enjoyable. It also (sometimes) helps with “pair bonding”.
I suppose the whole thing about why it takes a while and can only repeated after a break (usually…) goes back to ensuring that it is only done when the time and partner choice is most appropriate. If it was as easy and repeatable as shaking hands (the mind boggles at the thought), then there’d be a lot les natural selection happening. Sometimes it seems there’s little enough selection happening as it is.
There’s the (typical men’s) joke about female orgasms:
Q:“Why do women have fewer orgasms than men?”
A: “Who cares!”
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### Author:  [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)
#### Post date: [January 4, 2010, 6:08pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/30 "2010-01-04T18:08:30Z")
I’m way too much into penis biology.
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### Author:  [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)
#### Post date: [June 10, 2015, 5:08pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/31 "2015-06-10T17:08:34Z")
Just learned a new word:
Here’s the money quote from [Wiki “baculum”](http://en.wikipedia.org/wiki/Baculum):
**Absence in humans**
Unlike other primates, humans lack an os penis or os clitoris; however, this bone is present but is much reduced among the great apes: in many ape species it is a relatively insignificant 10–20 mm structure. There are reported cases of human penis ossification following trauma,[18] and one reported case of a congenital os penis surgically removed from a 5-year-old boy, who also had other developmental abnormalities, including a cleft scrotum.[19] Clellan S. Ford and Frank A. Beach in Patterns of Sexual Behavior (1953), p. 30 say “Both gorillas and chimpanzees possess a penile bone. In the latter species the os penis is located in the lower part of the organ and measures approximately three-quarters of an inch in length.”[1] In humans, the rigidity of the erection is provided entirely through blood pressure in the corpora cavernosa.
It has been speculated that the loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is because humans “evolved a mating system in which the male tended to accompany a particular female all the time to try to ensure paternity of her children”[7] which allows for frequent matings of short duration. Observation suggests that primates with a baculum only infrequently encounter females, but engage in longer periods of copulation that the baculum makes possible, thereby maximizing their chances of fathering the female’s offspring. Human females exhibit concealed ovulation also known as ‘hidden estrus’, meaning it is almost impossible to tell when the female is fertile, so frequent matings would be necessary to ensure paternity.[7]
The evolutionary biologist[20] Richard Dawkins speculated in 1989 that the loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is a result of sexual selection by females looking for honest signals of good health in prospective mates. The reliance of the human penis solely on hydraulic means to achieve a rigid state makes it particularly vulnerable to blood pressure variation. Poor erectile function betrays not only physical states such as diabetes and neurological disorders but mental states such as stress and depression.[21]
A third view is that its loss in humans was a side-effect of neoteny during human evolution; it is noted that late-stage fetal chimpanzees lack a baculum.[22]
Also I learned about _argumentum ad baculum_, which I will use the next time I debate someone mugging me.
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### Author:  [@jayjay](https://boards.straightdope.com/u/jayjay)
#### Post date: [June 10, 2015, 7:01pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/32 "2015-06-10T19:01:34Z")
> [@Leo\_Bloom](#):
>
> Anteaters (the real ones, not the euphemism for uncircumcised human males) have four penises, two which ejacualate at a time. You can google it, also on utube where u can see the damn things, if you want. I’m not sure that would be a good or bad thing for humans…
SPINY anteaters (echidnas) which live in the weird little pocket of evolution known as Australia-And-Surroundings, and which are monotremes, completely unrelated to the true anteaters of South America.
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### Author:  [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)
#### Post date: [June 10, 2015, 9:28pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/33 "2015-06-10T21:28:05Z")
> [@Leo\_Bloom](#):
>
> One suggestion for this evolutionary waste of resources is that the human male, …
Compare that to the contrasting expenditure of resources of a human male having a constant erection.
Almost any activity (fighting, running, working) would be more difficult and less productive. To say nothing of the health effects – there’s a reason all those ads say “seek medical help if you have an erection lasting more than 3 hours”.
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### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [June 11, 2015, 10:01pm UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/34 "2015-06-11T22:01:42Z")
> [@t-bonham@scc.net](#):
>
> … “seek medical help if you have an erection lasting more than 3 hours”.
this erection discussion has been up for 5 years. It’s too late for medical help.
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### Author:  [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)
#### Post date: [June 12, 2015, 12:19am UTC](https://boards.straightdope.com/t/flaccid-to-erect-penises-almost-unique-in-humans/523205/35 "2015-06-12T00:19:39Z")
> [@WhyWhyWhy](#):
>
> And I’m thinking a bone would be so much cheaper than Viagra.
Back in the [http://www.caverject.com](http://www.caverject.com) (possibly NSFW) days, another pharmacist, a man no less, said, “Oh, heck, just give the guy a stick and some tape.”
😛
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