# Girls who have sex with relative strangers **URL:** \ **Category:** In My Humble Opinion\ **Created:** [January 12, 2009, 9:44am UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894 "2009-01-12T09:44:45Z")\ **Posts on this page:** 20\ **Page:** 11
**Author:** ![WhyNot](https://avatars.discourse-cdn.com/v4/letter/w/c77e96/32.png) [@WhyNot](https://boards.straightdope.com/u/WhyNot)\ **Post date:** [January 14, 2009, 8:28pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/201 "2009-01-14T20:28:50Z")
> [@WF\_Tomba](#): > > Very interesting. My question is, does the woman increase the chances that _her_ genes will be passed on by taking actions that foster more intense sperm competition among her mates? I don’t quite see how that would work. A woman with more mates is more likely to have an egg fertilized, and thus pass on her genes. More sperm more often means at least one viable sperm is likely to make it. Add in male infertility, and multiple partners makes even more reproductive sense for the female. Consider a case like King Arthur’s - if the Queen had taken a lover early in their marriage and secretly gotten pregnant by another man, Britain might have been the better for it! Many animals (birds, primates) which are seemingly monogamous have quite a bit of female infidelity going on. They run the numbers game - choose a lifemate who will help raise the young, but secretly copulate with other males to increase the chances of conception and the hardiness of the offspring. ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [January 14, 2009, 8:38pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/202 "2009-01-14T20:38:33Z")
A woman increases the chances of her genes being passed on by ensuring that (1) She acquires the “best” genes for her offspring, and (2) by acquiring the most secure/affluent family structure in which that offspring will be raised. Good genes will offer the benefit of physical attributes, including an offspring that will be able to attract the “best” mate down the road. Financial security and good parenting (husbandry? 🙂 ) will ensure that the child grows to adulthood in health. In those situations in which the best genes and the best security can’t be matched up in one man, the evolutionary motivation is for the woman to ensure that the genetic father of her child comes from the best gene provider but for the “social” father to be the best money provider. This also plays a part in the mystery of human female fertility. Human females don’t go into heat or display reddened and swollen backsides when they are fertile. The woman’s interest is for her sexual partners not to know when she is actually fertile, so she can go about collecting the best genes without letting on to her partners. ---
**Author:** ![WF\_Tomba](https://avatars.discourse-cdn.com/v4/letter/w/d9b06d/32.png) [@WF\_Tomba](https://boards.straightdope.com/u/WF_Tomba)\ **Post date:** [January 14, 2009, 8:54pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/203 "2009-01-14T20:54:27Z")
I understand the benefit to the woman in diversifying her sperm sources, but what I don’t understand is how the _competition_ among the sperm in the reproductive tract factors into it. It’s obviously advantageous to the man to have fast-swimming sperm, since it makes his sperm more likely to beat the others. But assuming the woman has enough partners, one of them is bound to cross the goal line. So as far as I can tell, the only advantage that a fast sperm mate confers on the _woman’s_ genes is the likelihood that her male children will also have fast sperm. That’s an advantage that doesn’t even appear until a generation later–is that really enough to make it useful for the woman to use a mating strategy that rewards fast sperm? Or is the fostering of sperm competition just a side effect of a female strategy of diversifying her sperm sources? ---
**Author:** ![Unintentionally\_Blank](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/unintentionally_blank/32/5418_2.png) [@Unintentionally\_Blank](https://boards.straightdope.com/u/Unintentionally_Blank)\ **Post date:** [January 14, 2009, 9:02pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/204 "2009-01-14T21:02:27Z")
Well, assuming she’s having sex with one or more partners, no matter which guy wins, her genetic makeup gets a 50% vote. Paraphrasing loosely, she wants the best sperm to win, and the most dependable man to care for the result. ---
**Author:** ![WF\_Tomba](https://avatars.discourse-cdn.com/v4/letter/w/d9b06d/32.png) [@WF\_Tomba](https://boards.straightdope.com/u/WF_Tomba)\ **Post date:** [January 14, 2009, 9:03pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/205 "2009-01-14T21:03:48Z")
> [@Unintentionally\_Blank](#): > > Well, assuming she’s having sex with one or more partners, no matter which guy wins, her genetic makeup gets a 50% vote. That being the case, why does she want the best sperm to win? ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [January 14, 2009, 9:14pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/206 "2009-01-14T21:14:03Z")
“Faster sperm” is not the operative word here. It’s much more complicated than that. But just assuming we accept “faster” as a shorthand, that’s part of the male strategy. The woman doesn’t necessarily want the faster sperm to win. But her strategies are based on the assumption that there will be sperm competition going on. As I said, there’s a theory that the female orgasm may be used to favor one partner’s sperm over other partners’ sperm. ---
**Author:** ![Unintentionally\_Blank](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/unintentionally_blank/32/5418_2.png) [@Unintentionally\_Blank](https://boards.straightdope.com/u/Unintentionally_Blank)\ **Post date:** [January 14, 2009, 9:19pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/207 "2009-01-14T21:19:02Z")
Well, you’re propagating YOUR part of the DNA, do you want it attached to a good lookin’ healthy kid with all fingers an toes, or just ‘whatever comes first’? (oh that’s a **loaded** statement.) ---
**Author:** ![WF\_Tomba](https://avatars.discourse-cdn.com/v4/letter/w/d9b06d/32.png) [@WF\_Tomba](https://boards.straightdope.com/u/WF_Tomba)\ **Post date:** [January 14, 2009, 9:21pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/208 "2009-01-14T21:21:36Z")
> [@Unintentionally\_Blank](#): > > Well, you’re propagating YOUR part of the DNA, do you want it attached to a good lookin’ healthy kid with all fingers an toes, or just ‘whatever comes first’? (oh that’s a **loaded** statement.) Does better sperm actually correlate with the health or proper development of the offspring? ---
**Author:** ![Unintentionally\_Blank](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/unintentionally_blank/32/5418_2.png) [@Unintentionally\_Blank](https://boards.straightdope.com/u/Unintentionally_Blank)\ **Post date:** [January 14, 2009, 9:27pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/209 "2009-01-14T21:27:17Z")
uh…yes? It’s not my field of expertise, so I wouldn’t quote me in your thesis. 😉 ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [January 14, 2009, 9:35pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/210 "2009-01-14T21:35:37Z")
Refer to post 206 please. ---
**Author:** ![WF\_Tomba](https://avatars.discourse-cdn.com/v4/letter/w/d9b06d/32.png) [@WF\_Tomba](https://boards.straightdope.com/u/WF_Tomba)\ **Post date:** [January 14, 2009, 9:39pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/211 "2009-01-14T21:39:36Z")
> [@Unintentionally\_Blank](#): > > uh…yes? > > It’s not my field of expertise, so I wouldn’t quote me in your thesis. 😉 I am just trying to cast doubt on the idea that more successful sperm means “good genes” which means a more successful offspring. I don’t think it works that way. **acsenray** , your post 206 doesn’t quite settle all my questions, but you seem to be thinking along the same lines. ---
**Author:** ![DianaG](https://avatars.discourse-cdn.com/v4/letter/d/7ab992/32.png) [@DianaG](https://boards.straightdope.com/u/DianaG)\ **Post date:** [January 14, 2009, 9:44pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/212 "2009-01-14T21:44:32Z")
Not my area of expertise either, but it seems reasonable to presume that healthier people produce healthier eggs and sperm. Not necessarily smarter or prettier, but healthier. ---
**Author:** ![Dublin11](https://avatars.discourse-cdn.com/v4/letter/d/3ec8ea/32.png) [@Dublin11](https://boards.straightdope.com/u/Dublin11)\ **Post date:** [January 14, 2009, 10:15pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/213 "2009-01-14T22:15:25Z")
> [@DianaG](#): > > Not my area of expertise either, but it seems reasonable to presume that healthier people produce healthier eggs and sperm. Not necessarily smarter or prettier, but healthier. But if that was the case, then no healthy person would ever be infertile. I don’t think that’s true, is it? ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [January 14, 2009, 10:25pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/214 "2009-01-14T22:25:19Z")
> [@Dublin11](#): > > But if that was the case, then no healthy person would ever be infertile. I don’t think that’s true, is it? It’s argueable that if you are not fertile, you are not healthy – by definition. Except in those cases where you deliberately interfere with your own fertility. ---
**Author:** ![Dublin11](https://avatars.discourse-cdn.com/v4/letter/d/3ec8ea/32.png) [@Dublin11](https://boards.straightdope.com/u/Dublin11)\ **Post date:** [January 14, 2009, 10:29pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/215 "2009-01-14T22:29:14Z")
> [@Boyo\_Jim](#): > > It’s argueable that if you are not fertile, you are not healthy – by definition. Except in those cases where you deliberately interfere with your own fertility. Is that an accepted medical definition? I’ve not heard of it, but I can see how it makes sense. ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [January 14, 2009, 10:34pm UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/216 "2009-01-14T22:34:14Z")
> [@WF\_Tomba](#): > > **acsenray** , your post 206 doesn’t quite settle all my questions, but you seem to be thinking along the same lines. I’m no expert, but I’m happy to try to explore some of those other questions. By the way, you might pick up a copy of Robin Baker’s _Sperm Wars_. But “better sperm” is definitely an advantage for the man, not for the woman. The reason that better sperm is an advantage is that when a guy’s sperm gets to the uterus and other locations in the female reproductive system, there’s a good chance there are going to be other guys’ sperm there that have to be outdone. Not all sperm are “swimmers.” There are also “killers” and “blockers” – that is, sperm that are there to help the swimmers get through the competition. Kind of like a football team. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [January 15, 2009, 1:28am UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/217 "2009-01-15T01:28:39Z")
> [@Dublin11](#): > > Is that an accepted medical definition? I’ve not heard of it, but I can see how it makes sense. Oh, no I just made it up. But it does make sense. 😛 ---
**Author:** ![devilsknew](https://avatars.discourse-cdn.com/v4/letter/d/4da419/32.png) [@devilsknew](https://boards.straightdope.com/u/devilsknew)\ **Post date:** [January 15, 2009, 1:36am UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/218 "2009-01-15T01:36:32Z")
> [@Helen\_s\_Eidolon](#): > > Sex is always between people on an unequal footing? Gosh, I’m glad I don’t live in your world. Yea, somebody is always the top or the bottom. Somebody is always pitching… somebody is batting. It’s not unidirectional either… it is a very dynamic situation. Back and forth, round and round, from the back to the middle and round again. Dom Sub… what’s your kink, Helen? ---
**Author:** ![devilsknew](https://avatars.discourse-cdn.com/v4/letter/d/4da419/32.png) [@devilsknew](https://boards.straightdope.com/u/devilsknew)\ **Post date:** [January 15, 2009, 2:22am UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/219 "2009-01-15T02:22:05Z")
100% pure love. ---
**Author:** ![Helen\_s\_Eidolon](https://avatars.discourse-cdn.com/v4/letter/h/8edcca/32.png) [@Helen\_s\_Eidolon](https://boards.straightdope.com/u/Helen_s_Eidolon)\ **Post date:** [January 15, 2009, 4:16am UTC](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894/220 "2009-01-15T04:16:18Z")
My kink is coherence. Sorry, **devilsknew** , it’ll never work out between us. [Previous page](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894.md?page=10) [Next page](https://boards.straightdope.com/t/girls-who-have-sex-with-relative-strangers/480894.md?page=12)