Dolly is a little female baboon with a problem. Her problem is that she must suffer through the discomfort of active estrous swellings without being able to reproduce. Something else in her reproductive system isn't quite mature yet, so... no babies for her. This is nothing out of the ordinary; as far as I've been able to discern, all sub-adult females go through a phase such as this before becoming pregnant for the first time. A juvenile female becomes a sub-adult when her first swelling appears, and a full fledged female when she become pregnant. Or gives birth. Baboonists tend to argue about these definitions from time to time.
Unfortunately for Dolly, she tends to be ignored by the prime meat of the troop. This doesn't stop her from trying, however. One particular day, I noticed her hanging around Aaron for nearly an hour, berating him ever couple minutes with the swollen pink flesh of her rear end. He'd just be sitting on a rock, solemnly gazing out across the expanses of his females, and suddenly there would be a bright female butt thrust into his face. If she was lucky, he'd glance at her before returning to his seemingly emotionless survey of the troop. Quite a far cry from a gruntalicious copulation.
But there's always a chance.
Chasing after Aaron is not risk free, however. The adult females, particular the top ranked one, often take great offense at Dolly and young/low ranked females when they attempt to solicit attention from Aaron. Some serious beatings have resulted from young females stepping out of line.
Thus, Dolly makes due with younger males, some of which are smaller than she is. If she's lucky, Janny, one of the sub-adults will take interest in her for a few days, but as soon as a fertile adult female becomes "available" he'll be off to greener pastures with her.
Dolly has an active, if slightly underpowered sex drive and no way to get rid of it (i.e. pregnancy). There's not a lot else to do but obey the urges until her system comes fully online in a year or so and pregnancy hits. Its unclear if the males have any understanding of her infertility. The young guys are still all over her, but then again, they might just be acting out their own sex drives, which as I've established, is quite strong in males at a young age.
There are many other females who Aaron regularly ignores - he sticks to the top 4 or 5 females usually, sometimes even when they're clearly not capable of becoming pregnant: for the first few cycles after giving birth the female's hormones aren't right for reproduction. But Aaron doesn't seem to care, he keeps going at it with Lottie. Why not go after every female possible? He could do it, he's the strongest alpha male in the entire locality, he might have to give up some extra-pair copulations for some of the females, but that'd be a small price.
If Aaron isn't doing it though, he must have a good reason. The subconscious is way smarter than any reasoning can be, after all. Sperm competition and its extremely intricate and complex guidelines (which we only are beginning to understand) indicates a few possibilities, for instance, Aaron wouldn't want to decrease the quality of his sperm balance by rampantly copulating without forethought. Even in the monkey world, you can't just have indiscriminate sex all the time. Paradise can be such a drag.