# Why do men need to thrust and stroke to achieve ejaculation? **URL:** \ **Category:** Factual Questions\ **Created:** [May 17, 2002, 8:07pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608 "2002-05-17T20:07:19Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![CnoteChris](https://avatars.discourse-cdn.com/v4/letter/c/278dde/32.png) [@CnoteChris](https://boards.straightdope.com/u/CnoteChris)\ **Post date:** [May 17, 2002, 8:07pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/1 "2002-05-17T20:07:19Z")
Think about it. It’s not like you’re pumping something up, like a basketball, you don’t need the pressure built up somewhere, only to be released at a different time, all that stuff is handled involuntary and by specific internal muscles. But most males, and even males of different species even, need the act of stroking and/or thrusting of the penis for them to reach orgasm. Why? Outside of making it more exciting- for those of us doing it for fun- why would natural selection (If that’s what’s in play here) make it harder for one to reproduce (I.e. the thrusting and stroking and whatnot) rather than, say, simply sticking it in there and letting it fly? It seems to me that the second method would be easier and less costly to the male in terms of energy output and all that. But that’s not the case for any number of males, and for any number of species- their thrusting away like mad as if it was necessary. So, why? ---
**Author:** ![DarrenS](https://avatars.discourse-cdn.com/v4/letter/d/977dab/32.png) [@DarrenS](https://boards.straightdope.com/u/DarrenS)\ **Post date:** [May 17, 2002, 8:16pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/2 "2002-05-17T20:16:55Z")
Total guess - but maybe for evolutionary reasons, it’s not a good idea for the male to release his sperm _too_ easily - it’s not good for procreation if he wastes it. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [May 17, 2002, 8:17pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/3 "2002-05-17T20:17:41Z")
The more effort that’s required to ejaculate, the less likely it is to happen accidentally. Fewer sperm are wasted that way. ---
**Author:** ![NurseCarmen](https://avatars.discourse-cdn.com/v4/letter/n/5daacb/32.png) [@NurseCarmen](https://boards.straightdope.com/u/NurseCarmen)\ **Post date:** [May 17, 2002, 8:36pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/4 "2002-05-17T20:36:34Z")
I recall a commercial that aired in Aisa to discourage the use of Tiger testicles as an herbal “viagra”. They showed the male tiger mating, and it was over in an instant. The commercial implied that if you want longevity in the sack, do you really want to get it from this two second beast? So count Tigers and men with a case of the preemies (5 minute Phil, two minute Tony, and Premature Pete) as exceptions to this phenomena. ---
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [May 17, 2002, 8:39pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/5 "2002-05-17T20:39:32Z")
To get picky, what about wet dreams? No physical movement there. Of course, you _think_ you’re doing the nasty… [sub]at least, most of us are…[/sub] ---
**Author:** ![CnoteChris](https://avatars.discourse-cdn.com/v4/letter/c/278dde/32.png) [@CnoteChris](https://boards.straightdope.com/u/CnoteChris)\ **Post date:** [May 17, 2002, 8:52pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/6 "2002-05-17T20:52:33Z")
> [@](#): > > \*Originally posted by ultrafilter \* > \*\*Fewer sperm are wasted that way. \*\* If waste is an issue, than I’m a dead man. I’ve shot more of my DNA into thin air and tissues than has ever made it into the nether regions of a female, yet I still seem to have enough to go around come the time when I want to concieve a child. The point is, I’m not too worried that I’m going to run out of the stuff. Because if I remember right, males pretty much have an unlimited amount of the stuff at their disposal, right? If that’s the case, than why would ‘waste’ be an issue? What got me, or gets me, about all this, is that it seems as if your pumping something up, or building up pressure, for the ‘event’ to take place, but that’s not happening at all, right? There’s really no need, but everyone seems to do it. \*Preview reveals **Bernse’s** wet dream comment- Exactly- thrusting, stroking, anything else that comes to mind, isn’t really necessary for ejaculation, but it’s done as if it is. That’s why this fascinates me about all this- why the effort? ---
**Author:** ![scott\_evil](https://avatars.discourse-cdn.com/v4/letter/s/91b2a8/32.png) [@scott\_evil](https://boards.straightdope.com/u/scott_evil)\ **Post date:** [May 17, 2002, 8:58pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/7 "2002-05-17T20:58:20Z")
> [@](#): > > \*Originally posted by bernse \* > **To get picky, what about wet dreams? No physical movement there.** I assume it’s the pressure of the erection against the mattress that causes ejaculation. My first boyfriend could have an orgasm just by putting pressure on the base of his dick - no stroking or thrusting at all. - s.e. ---
**Author:** ![bup](https://avatars.discourse-cdn.com/v4/letter/b/6bbea6/32.png) [@bup](https://boards.straightdope.com/u/bup)\ **Post date:** [May 17, 2002, 8:58pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/8 "2002-05-17T20:58:21Z")
WAG: It takes some effort, not because the male’s body is trying to conserve sperm, but because females get to be more selective that way. Sure, rape exists, but a man who has sex with a woman is much more likely to be with a willing partner, simply because it is a little bit of an involved activity. ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [May 17, 2002, 8:58pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/9 "2002-05-17T20:58:25Z")
It seems that sufficient friction is the trigger that tells the brain to start your orgasm: From [the Merck Manual](http://www.merck.com/pubs/mmanual_home/sec21/228.htm): > [@](#): > > Ejaculation occurs at the climax of sexual excitement when friction on the glans penis and other stimuli send signals to the brain and spinal cord. Nerves stimulate muscle contractions along the ducts of the epididymis and vas deferens, the seminal vesicles, and the prostate. These contractions force semen into the urethra. Contraction of the muscles around the urethra further propels the semen through and out of the penis. The neck of the bladder also constricts to keep semen from flowing backward into the bladder. From [the University of Virginia](http://www.people.virginia.edu/~rjh9u/lect31.html): > [@](#): > > Male > Friction between the vaginal walls and the penile glans and shaft stimulates nerve endings. > The muscles in the scrotum contract raising the scrotum closer to the torso. > Muscles in the epididymis and vas deferans contract moving the sperm through the vas deferans. > Secretions from the seminal vesicle and prostrate gland are mixed with the advancing sperm. There are other links that I hesitate to provide in accordance with board rules, even though they are scholarly in nature (some have illustrations). But if you google for “friction male ejaculation”, you’ll find plenty of sources. ---
**Author:** ![jhwood9](https://avatars.discourse-cdn.com/v4/letter/j/9e8a1a/32.png) [@jhwood9](https://boards.straightdope.com/u/jhwood9)\ **Post date:** [May 17, 2002, 8:59pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/10 "2002-05-17T20:59:40Z")
It was my understanding that thrusting was a mechanical process necessary for a species in which groups of males try to impregnate a single female. I’m no procreational expert, but I seem to recall that sex researchers have identified three different types of sperm… ones that aggressively seek out and kill sperm cells with a different DNA pattern (aggressive attack), ones that form mucus barriers (“soft plug,” or passive attack), and swimmers which only try to find the egg cell. The thrusting motion is necessary to break up the “soft plug” of sperm in the cervix of a woman who had already experienced coitus, allowing the woman’s current partner a better chance to impregnate her with his own sperm. ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [May 17, 2002, 9:28pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/11 "2002-05-17T21:28:54Z")
Yeah, I realized before I read **jhwood9** ’s post that the real reason is that we are a soft-plug species, and so the thrusting serves to break up the sperm. My earlier guess was simply a guess, and should’ve been id’d as such. ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [May 17, 2002, 9:32pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/12 "2002-05-17T21:32:37Z")
I’ve heard the same theory as jhwood9. It’s a result of the fact that humans live in mixed-sex social groups, and women have no obvious outwards signs of ovulation. So, there’s no way for a guy to make sure he’s the only one having sex with a woman during her fertile period. So, in addition to developing sperm which form a soft, sticky plug over the cervix to bar entry to other men’s sperm, we’ve developed large plunger-like penises and a prolonged sexual act which helps wash away the sperm left by another man. ---
**Author:** ![jmpride62](https://avatars.discourse-cdn.com/v4/letter/j/c37758/32.png) [@jmpride62](https://boards.straightdope.com/u/jmpride62)\ **Post date:** [May 17, 2002, 9:41pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/13 "2002-05-17T21:41:53Z")
Also, something I’ve wondered wouldn’t the ability to procreate increase if more men were capable of several ejaculations in rapid fashion? I would think that having a willing female, nature would want to make it possible for a man to ‘flood’ (for lack of a better term) the vagina to make procreation more likely. Just a thought ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [May 17, 2002, 9:58pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/14 "2002-05-17T21:58:48Z")
Is there something wrong with the Merck study and U Va cites? ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 17, 2002, 10:16pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/15 "2002-05-17T22:16:11Z")
The typical thrush that we all know is what circiumsized men must do to ‘feel’ enough to ‘come’. Un-cir men are more ‘gental’ so to speak and do less thrusting and more ‘moving’. or so I’ve heard on a Dr. radio show. Also the time it requires to come might have something to do with inducing an orgasim in the female which might aid fertilization. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [May 17, 2002, 10:44pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/16 "2002-05-17T22:44:01Z")
We can look at the comparative anatomy of hominoids. Gorillas have small testes/amount of ejaculate, humans have medium size testes, and chimps have large testes. Gorillas live in single-male harems, so there isn’t much sperm competition. There is very little likelyhood of two male gorillas mating with the same female at close to the same time. Chimps live in mixed-sex bands, and it is common for all the males in a band to mate with a female in estrous. This means that there is a great deal of sperm competition, and males who produce the most sperm are selected for. Humans are intermediate…human females often mate with only one male during their fertile period, but aren’t as exclusive as gorillas. ---
**Author:** ![CnoteChris](https://avatars.discourse-cdn.com/v4/letter/c/278dde/32.png) [@CnoteChris](https://boards.straightdope.com/u/CnoteChris)\ **Post date:** [May 18, 2002, 7:04am UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/17 "2002-05-18T07:04:07Z")
Lib, dude, just because everyone doesn’t jump behind your conclusion doesn’t mean their thoughts are wrong… some people believe the exact opposite. Come on lib, don’t ruin it for everyone else. There seems to be a lot more to it, this ‘plug’ thing I don’t quite understand, but hey, it’s the deal. Come on someone, explain it to me in a way that makes sense… ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [May 18, 2002, 11:12am UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/18 "2002-05-18T11:12:16Z")
I don’t mean to ruin anything, and that’s not my conclusion. It’s the conclusion of doctors from one of the finest medical research laboratories in the world, and from a human sexual response lecture at a major university. If you don’t consider them to be credible sources, I’d like to know why. Your question has been answered with step by step expository. Men need to thrust and stroke in order to create friction, whereupon their brains set into motion the process that leads to ejaculation. ---
**Author:** ![Fenris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fenris/32/498_2.png) [@Fenris](https://boards.straightdope.com/u/Fenris)\ **Post date:** [May 18, 2002, 12:33pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/19 "2002-05-18T12:33:27Z")
> [@](#): > > \*Originally posted by Libertarian \* > \*\*If you don’t consider them to be credible sources, I’d like to know why. Your question has been answered with step by step expository. Men need to thrust and stroke in order to create friction, whereupon their brains set into motion the process that leads to ejaculation. \*\* Ok, but that just takes the question back one step further: why does the brain “require” the friction trigger to ejaculate? Why not pressure ( **Scott Evil’s** boyfriend being the execption) or putting your penis somewhere warm and moist? Is there something advantatgeous evolutionarily about the thrust/friction thing? BTW: My understanding based on an article I read somewhere [sup]\*[/sup] was that the friction “overstimulated” the nerves somehow which caused the ejaculation… Fenris [sup]\*[/sup] Comic-Book Guy “Worst. Cite. Ever.” ---
**Author:** ![LolaBaby](https://avatars.discourse-cdn.com/v4/letter/l/d2c977/32.png) [@LolaBaby](https://boards.straightdope.com/u/LolaBaby)\ **Post date:** [May 18, 2002, 12:43pm UTC](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608/20 "2002-05-18T12:43:03Z")
> [@](#): > > \*Originally posted by k2dave \* > \*\* > Also the time it requires to come might have something to do with inducing an orgasm in the female which might aid fertilization. \*\* I remember reading on here somewhere about that “penis-cam” that showed the cervix “dipping” into the pool of sperm if _both_ partners reached simultaneous orgasm, thus enhancing a man’s chances of keeping his gene pool alive. [Next page](https://boards.straightdope.com/t/why-do-men-need-to-thrust-and-stroke-to-achieve-ejaculation/109608.md?page=2)