# The evolutionary placement of genitalia **URL:** \ **Category:** Factual Questions\ **Created:** [October 14, 2014, 11:36am UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289 "2014-10-14T11:36:15Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [October 14, 2014, 11:36am UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/1 "2014-10-14T11:36:15Z")
It seems like with many current animals, the penis and vagina are often located just in front or otherwise near the buttocks, somewhere on the pelvis. Evolutionarily, was this the case? Are there animals with strangely-placed genitalia, either extant or in the fossil record? [Leopard slugs](https://www.youtube.com/watch?v=wG9qpZ89qzc) are the only thing that come to mind for me. Which others are there? ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [October 14, 2014, 1:18pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/2 "2014-10-14T13:18:41Z")
> [@Reply](#): > > [Leopard slugs](https://www.youtube.com/watch?v=wG9qpZ89qzc) are the only thing that come to mind for me. Which others are there? > [@](#): > > This video is not available in your country. And I am in Britain and it is a BBC video, dammit! I paid for it, with my license fee, and I am not allowed to watch it, but it seems like people in other countries, who did not pay for it, are! :mad: I have got a good mind to rearrange some BBC person’s genitals! ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [October 14, 2014, 1:29pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/3 "2014-10-14T13:29:59Z")
Bear in mind that for most organisms, holes connecting your internal organs with the outside environment make you kind of vulnerable. Not to go all “Just-So Stories” on the accidents of evolution, but it does make a fair bit of sense that such holes should be concentrated in specific areas that you can protect. Thus, e.g., for mammals our holes are located either in the “command tower” at the front end of our torsos, where most of the data gathering takes place and potential threats are most readily noticed, or in the “engine room” at the other end, tucked into the crevice between our hind limbs which is better shielded from immediate contact with all the things we go around sticking our heads and paws into. ---
**Author:** ![muldoonthief](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/muldoonthief/32/3188_2.png) [@muldoonthief](https://boards.straightdope.com/u/muldoonthief)\ **Post date:** [October 14, 2014, 1:48pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/4 "2014-10-14T13:48:11Z")
What’s the joke? God must be a civil engineer - who else would route wastewater disposal through a recreational facility? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 14, 2014, 2:46pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/5 "2014-10-14T14:46:28Z")
The commonality of placement amongst vertebrates is most likely due to ancestral body plan - so we need to look further afield, however, many of the organisms in other phyla don’t actually copulate at all - they just release gametes - so they don’t have anything like a penis or vagina. ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [October 14, 2014, 3:36pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/6 "2014-10-14T15:36:30Z")
[More detail:](http://www.leeds.ac.uk/chb/lectures/anatomy9.html) > [@](#): > > During the process of evolution we quite often find that structures evolved to do one thing are no longer relevant. […] these relict organs may be taken over for quite another purpose. This is the case with the excretory and reproductive systems which are anatomically and evolutionary linked, and where parts of the excretory system have been taken over by the reproductive system. > > To understand this we must go back to our coelomate ancestor. > > Remember this had a gut and a coelom lined with thin mesothelium. Now a large cavity with a thin wall like this is ideal for dumping waste, and it seems that the coelom was so used. The result, of course is that it would gradually fill with ions, salts, water and what have you. This seems to have been countered by forming paired lateral ducts, lined with cilia and called nephrotomes. > > The cilia control the direction of the fluid, outwards. Interestingly these excretory ducts probably also carried gametes to the sea, even at this early stage. > > Now the animals we are talking about were segmented, like sliced bread, and had one coelom and one pair of nephrotomes per segment. When segmentation was abandoned in favour of an open plan coelom the nephroptomes became rationalised with paired openings (still) but only one exit to the sea, towards the rear. The open plan coelom developed at about the same time as the circulatory system, and this became involved. […] > > This set-up, a glomerulus, a nephric tubule (essentially a space) and a duct passing posteriorly has formed the basis of the kidneys ever since. I say kidneys not because we have two of them but because during vertebrate history there have been three pairs of kidneys. The most primitive of these was anterior, the next more posterior and the last most posterior. They are called pronephros, mesonephros and metanephros. […] > > The gonads develop in the same dorsolateral region as the kidneys. Gonads are initially equipped with two sets of ducts. Why? Well remember that nephrotomes, ciliated ducts passing to the outside originally carried germ cells. When the connection to the coelom was lost an alternative duct system, the parmesonephric ducts were developed to provide passage for the germ cells. When, in turn the mesonephric duct became redundant it was reclaimed by the reproductive system. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 14, 2014, 3:41pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/7 "2014-10-14T15:41:49Z")
Well, they have something _like_ a penis or vagina, in that they release gametes from some specific organ. And even in nonvertibrates, that organ is often at the posterior end of the body, near the anus. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [October 14, 2014, 4:10pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/8 "2014-10-14T16:10:00Z")
I’ve often wondered why male seals and walruses, sliding over rocks, don’t have to wear a cup. ---
**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:** [October 14, 2014, 4:27pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/9 "2014-10-14T16:27:44Z")
> [@jtur88](#): > > I’ve often wondered why male seals and walruses, sliding over rocks, don’t have to wear a cup. Because they retract their genitalia into their bodies. If you look at a male walrus he’s just got a slit–until it’s business time. Then out comes the wedding tackle, reinforced with a two foot long bone. Like, a literal bone. Native Alaskans used to use them as war clubs. ---
**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\ **Post date:** [October 14, 2014, 4:33pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/10 "2014-10-14T16:33:46Z")
> [@jtur88](#): > > I’ve often wondered why male seals and walruses, sliding over rocks, don’t have to wear a cup. Excellent. As well as quick, to the point, and accurate reply. With weird fun fact as lagniappe. Classic GQ. If it were me, that would have been the subject hed of an OP… ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [October 14, 2014, 4:42pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/11 "2014-10-14T16:42:33Z")
> [@Lemur866](#): > > Because they retract their genitalia into their bodies. If you look at a male walrus he’s just got a slit–until it’s business time. Then out comes the wedding tackle, … Much like sumo wrestlers? ---
**Author:** ![standingwave](https://avatars.discourse-cdn.com/v4/letter/s/9de0a6/32.png) [@standingwave](https://boards.straightdope.com/u/standingwave)\ **Post date:** [October 14, 2014, 5:30pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/12 "2014-10-14T17:30:34Z")
> [@muldoonthief](#): > > What’s the joke? God must be a civil engineer - who else would route wastewater disposal through a recreational facility? Could be worse. We could have [these](http://en.wikipedia.org/wiki/Cloaca)… In zoological anatomy, a cloaca /kloʊˈeɪkə/ is the posterior opening that serves as the only opening for the intestinal, reproductive, and urinary tracts of certain animal species. All amphibians, birds, reptiles, and monotremes possess this orifice, from which they excrete both urine and feces, unlike most placental mammals, which possess two or three separate orifices for evacuation. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 14, 2014, 5:53pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/13 "2014-10-14T17:53:19Z")
> [@Chronos](#): > > Well, they have something _like_ a penis or vagina, in that they release gametes from some specific organ. Not really. A penis is pretty specifically a copulatory device. A duct that releases semen is by no means necessarily a penis and a duct that releases ova probably isn’t actually a vagina. ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [October 14, 2014, 7:20pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/14 "2014-10-14T19:20:12Z")
> [@Mangetout](#): > > Not really. A penis is pretty specifically a copulatory device. No way. It’s a religious device. [Cite](http://en.wikipedia.org/wiki/Apotropaic_magic). > [@](#): > > In [Ancient Greece](http://en.wikipedia.org/wiki/Ancient_Greece), **[phalli](http://en.wikipedia.org/wiki/Phalli)** were believed to have apotropaic qualities. Often stone reliefs would be placed above doorways, and three-dimensional versions were erected across the Greek world. ETA : apotropaic means “wards off evil spirits” ---
**Author:** ![Orwell](https://avatars.discourse-cdn.com/v4/letter/o/dfb087/32.png) [@Orwell](https://boards.straightdope.com/u/Orwell)\ **Post date:** [October 14, 2014, 7:22pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/15 "2014-10-14T19:22:35Z")
> [@muldoonthief](#): > > What’s the joke? God must be a civil engineer - who else would route wastewater disposal through a recreational facility? Or, you know that God must be a Polack\*. Who else would put the snack bar right next to the shithouse? - I know, derogatory and offensive, but essential to the joke. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [October 14, 2014, 8:07pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/16 "2014-10-14T20:07:34Z")
> [@Orwell](#): > > Or, you know that God must be a Polack\*. Who else would put the snack bar right next to the shithouse? > > - I know, derogatory and offensive, but essential to the joke. **Moderator Note** Let’s save derogatory and offensive jokes for the next “Tell me your most derogatory and offensive jokes” thread in MPSIMS. No warning issued. (And no, inclusion of a specific ethnic group isn’t essential to the joke. You could have just said [insert ethnic group of your choice].) Colibri General Questions Moderator ---
**Author:** ![Toucanna](https://avatars.discourse-cdn.com/v4/letter/t/3bc359/32.png) [@Toucanna](https://boards.straightdope.com/u/Toucanna)\ **Post date:** [October 14, 2014, 9:04pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/17 "2014-10-14T21:04:58Z")
[QUOTE=Orwell] Or, you know that God must be a [redacted]. {snip} [/QUOTE] Next time, substitute “Aggie” for [redacted]. That’s classic humor there, my son. 😛 Now that the legit answers have been supplied, I’ll leave you with a nugget of philosophical wisdom I’ve said for years: “If God didn’t us to masturbate, he shouldn’t have made our arms long enough for our hands to reach our genitals.” --Toucanna Thank you, thank you, and please remember to include the attribution when you quote me. 😃 ---
**Author:** ![Flywheel](https://avatars.discourse-cdn.com/v4/letter/f/eb8c5e/32.png) [@Flywheel](https://boards.straightdope.com/u/Flywheel)\ **Post date:** [October 14, 2014, 9:28pm UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/18 "2014-10-14T21:28:12Z")
> [@muldoonthief](#): > > What’s the joke? God must be a civil engineer - who else would route wastewater disposal through a recreational facility? [Darwin](http://www.smbc-comics.com/?id=3169) doesn’t do jokes. ---
**Author:** ![rsa](https://avatars.discourse-cdn.com/v4/letter/r/839c29/32.png) [@rsa](https://boards.straightdope.com/u/rsa)\ **Post date:** [October 15, 2014, 4:52am UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/19 "2014-10-15T04:52:01Z")
> [@Reply](#): > > It seems like with many current animals, the penis and vagina are often located just in front or otherwise near the buttocks, somewhere on the pelvis. > > Evolutionarily, was this the case? Are there animals with strangely-placed genitalia, either extant or in the fossil record? > > [Leopard slugs](https://www.youtube.com/watch?v=wG9qpZ89qzc) are the only thing that come to mind for me. Which others are there? See Fig. 10 of the [female elephant](http://www.asianelephantresearch.com/about-elephant-anatomy-and-biology-p4.php). The anus is nowhere near the vulva. The vagina is up inside the back of the elephant connected to the vulva via a very long vestibule (which in humans is only a few cm IIRC.) There was an interesting TV show (a series about animal sex?) that I stumbled across. The researchers had to collect semen so they anesthetized the male and inserted a _ **very** _ large electrical device in the rectum to stimulate an erection. With the help of a bit of stroking by the attractive female researcher they were able to collect a rather small sample using an elbow high rubber glove as a condom / collection device. ---
**Author:** ![Kobal2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kobal2/32/20_2.png) [@Kobal2](https://boards.straightdope.com/u/Kobal2)\ **Post date:** [October 15, 2014, 11:12am UTC](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289/20 "2014-10-15T11:12:32Z")
“So what do you do for a living, love ?” “Oh, you know, boring stuff. I jerk elephants off. Sorry, I meant: I’m a biology researcher.” [Next page](https://boards.straightdope.com/t/the-evolutionary-placement-of-genitalia/701289.md?page=2)