I started writing this a long time ago, and after reading through it and changing a couple of things, I discovered it was pretty much ready for publication here. There will be a second part to this globulation and it will be uploaded shortly. Perhaps if I was taller, it could be uploaded tall-ly, but unfortunately everything I ever post is posted shortly.
The second part to this globulation will answer the final question in this post: "When does sex end?"
I found this article on one of Skepchick's quickies which was found in Jesse Bering's article titled, "Not so fast... What's so premature about premature ejaculation?" on Scientific American.
"...in the ancestral past, wouldn’t there likely have been some reproductive advantages to ejaculating as quickly as possible during intravaginal intercourse—such as, oh, I don’t know, inseminating as many females as possible in as short a time frame as possible? or allowing our ancestors to focus on other adaptive behaviors aside from sex? or perhaps, under surreptitious mating conditions, doing the deed quickly and expeditiously without causing a big scene?"
The article talks about many good points relating to the biological reasons for men's ability to ejaculate quickly. It's for procreation. Men needed to distribute that sperm as widely as possible, so the less time it took for a man to climax, the more time he had to attempt impregnating another female. Women were just incubators, a means to populate the earth. With any luck, the man would deposit his sperm in a female during the proper time of her menstrual cycle and a little Incubator Jr. or Sperm-depositor Jr. would be conceived. However, this allows males to not be tied to his female, as she wouldn't be his at all, leaving the female to take care of the child on her own and the child to never know his father. That might have been fine back in the day, you know, when fire was a novelty, but we are now a civilized species, more or less. Most of us value the concept of a "family."
In addition, women are not just used for procreation anymore; at least they shouldn't be. Their ability to experience pleasure is taken under consideration during intercourse... some of the time. After all, the sole purpose of the clitoris is to provide pleasure; if we did not deserve to experience pleasure during sex, why bother having one?
Certain primates respond well to speedy ejaculation. "...macaque sex is a chaotic and violent affair, largely because the duration of the act often draws hostile attention from other competitive males" (Bering). Plus, the females probably just want to get it over with. On the other hand, certain species, including humans, sometimes find it hard to conceive if they are undergoing some form of stress during intercourse. Of course, this cannot be said for those impregnated during a rape; it does not mean the victim enjoyed it, as it was once believed, it simply means they are more able to conceive than others may be.
Premature ejaculation should not be seen as something negative and the man should not be blamed or ridiculed for it. However, this brings up a question that I've thought about many times: When does sex end?