Originally Posted by ZenBeam
I'm certain this occurred after the continuous stream of urine...
Why? I'm sure that even with a much lower frequency, the time spent having sex is longer than the time spent urinating (e.g. 1 minute (total) per day of urinating vs. 30 minutes* of sex, just once), and early humans were no doubt much more promiscuous than today.
*Of course, the time should be halved to account for the need for two people instead of one (assume no orgies) , but it is still significantly greater.