Well here is a biological condition to which I alluded above.
There is a chart in Sex at Dawn (read it), which shows the sizes of the penis and testicles in several species of ape, humans included. The testicles of bonobos, chimps and humans hang outside the body. The testicles of gorillas and gibbons are tiny in comparison to the others,' and are tucked up inside the body.
The first 3 have chilly testicles, which increases sperm production. They are meant to be used to take part in sperm competition with other males, having sex with the same female.
The head of the human male corona is extra large and works as a squeegee to scrape out another man's semen. Not mentioned in the book is the idea that women's watery ejaculate is produced to wash out semen, to make way for something better that just came along.
Loud female vocalizing during orgasm is a mating call to attract other men. "Ooh! Someone's in the mood." She is multi-orgasmic, while most men are good for just one shot (at least for an hour or so). So, the first guy or 2 are just warmups.