Observation: Population

My population has maxed out. I originally set my max creatures at 50, but once it became apparent they were getting rather crowded I lowered it to 45.
I've got my breeding limit set to 4 children per Norn, which should aid in keeping the population under control.

I have a couple of unhatched eggs lying about but only about 5 or so, which I don't find too distressing. If I start ending up with large stockpiles of eggs I'll consider lowering the breeding limit. My aim is to get a stable population that doesn't get bogged down by old eggs, nor do they go extinct due to a lack of breeding.

I'm a little concerned that the Grendels have stopped breeding and are no longer stockpiling eggs. I think I'm going to need them later as a selective pressure, as my Norns are surviving quite well.

As diabolical as it sounds I may need to considering introducing some things that will help kill off the weaker Norns. I want to see if I can get a stable population without doing so first, by limiting breeding. Then I'll introduce a few additional pressures and if needed up the breeding limit to accommodate.

I'd like whatever pressures I introduce to not be random, which will hopefully promote good evolution. For example having the piranha pit open periodically would be no good, as the Norns will have no concept of staying away.

I do have the bubonic bulge and macrobacteria in the world, so hopefully disease will be a contributing selective force, but I want a few other things to introduce.

The Grendels can't be relied on as selective pressures, as it looks like they might end up being out-bred, although the egg laying machines should always leave me with a couple.

Any ideas? What would be good selective pressures to apply to my tribes? Preferably pressures that don't kill them first shot and they can learn to avoid them in later life.