Alright, so I made this challenge up at school. I based it off of how real animals usually act.
There is technically more than one way to do this challenge, you can do it any way you want as long as it's in the rules.
SO,
Rules
1. Females only choose the strongest/prettiest males: Most female animals choose the strongest male for the best genetics for their offspring, and sometimes for protection of predators attack them or their children. Animals like peacocks choose the flashiest males most of the time, which I don't really know the purpose of. You could choose which genes are attractive but things like Peacock Tail will automatically make a creature attractive, and something like Derp Snout will severely lower a male's chances.
2. Any sick babies get killed: Animals in real life usually abandon and sometimes eat their sick children because they wont survive, and leaves her other, healthy offspring vulnerable to becoming ill, so she gets rid of it. Basically, if you get a sick child, kill them somehow.
3. No creature mates for life: You could have them pair up for 10 days or something, representing a breeding season like some birds do. Even then, no animal is truly monogamous, and birds will literally cheat on eachother. It's actually kind of funny.
4. A female's last offspring must have aged up to a teen(or an adult for extra challenge) for her to have another one. Unless it dies.
5. Males can compete with eachother: The winner gets to mate with the female, you can just roll a random generator for this.
6. If you want, any females that live in groups can try to eliminate the other children. Meerkats will do this, because they live in such big groups, less children means more attention for theirs.
That's all the rules I could come up with for now, but i'll probably update it later tho.