dye

Disagree.

Typically, a species with many sex partner will develope a very sophisticated sex organ (or large).  For example, bonobo's penis.  These fellow make love as much as we shake hands.  They do it when they are afraid, when they are happy, with member of the same sex, when they are playing, when they just meet each other....

They even masterbrate...


The reason is that when many male is mating with a female, it become vitally important to ensure that those before you are diluted by your entering, those behind you will be unable to outcompete you.

Human has a medium size penis among the primate, a clear sign that we are evolve to have few sex partners (don't ask me how few).
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The fact that ther are fewer and fewer sperm as a relationship is stablized demonstrate the point precisely.  As a relationship is stablize, there is no one before to compete, and no one after to take over.  The man can focus himself in rearing the young instead of producing sperms.
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The following diagram shows the relationship


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Then again, we can't get a "what is" to a "what should".

[ 本帖最後由 dye 於 2008-3-13 17:57 編輯 ]

dye

If I read correctly, solid black means "regular" relationship. Grey line means occasional relationship (like a one night stand)

Maybe this will help looking at the relative size of penis and breasts of different cousins of ours.



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If you ask me, I think Sherman is the role model of "natural" human.  Having a single wife for most of time, taking opportunities whenever she is away,  (Except that his wife will also be doing te same.)

Where as a gorilla is like Moses.  Have a few wives regularly and no outside affair.  (Except that his wife will be cheating behind his back)

[ 本帖最後由 dye 於 2008-3-14 08:54 編輯 ]