I found a way to sort of "break" Creatures 3...
Start the game off with the pre-trained breeding pair. Let them wander around and get acquainted while you sit and stare at the Grendel egg-layer. As soon as it pops out an egg, grab it and take it with you into the desert terrarium.
Once there, drop it into the little pool of water off to the side. There's likely an Ettin egg lying out in the open too, so stick that next to the Grendel egg. Now wait until the second Ettin egg gets spat out, and put it into the water along with the other two.
How this works is that both the Ettin and Grendel egglayers are self-regulating. There will always be two Ettins and one Grendel on the ship (actually, might be two... Long time since I played). Should the number ever fall below that, the respective egglayer will automatically pop out another one.
But here's the twist... Egg's will never hatch in water, but they still count as creatures. So, by leaving the eggs in the little pool of water, you have reached the sustained number of Grendels and Ettins, but will never actually have to deal with the annoying and disruptive little buggers.
This will give you all the time you need to lead your trained adult Norns around the ship in search of those system upgrades. With all that, you will really have an open playground for you to shape and manipulate.
And, should you ever desire the company of Ettins or Grendels again, just take one of the eggs out of the water. They should resume their natural process quickly enough.
Also, it does work as a life simulator in a sense. Not so much as a survivor thingy, unless you're really good at training your Norns, but you can try and work out an ecosystem that doesn't crash within the first few moments of the game (I.E., all those provided).
Has anyone ever actually done that? Made an environment that can sustain itself without having to leech off the ship's energy supply to restore an extinct species? If you leave things as they are, things will go completely nutso.
The Norn terrarium will lose all its dragonflies, who have been eaten by the trout. The trout then have nothing to eat, and so die off, causing the Kingfisher to starve. The entire right side of the terrarium just dies within the first half hour of the game. I think the same thing happens with those pig critters and the giant hawk, but I can't remember.
The desert terrarium will have those rocklickers die off due to a combination of no food (that volcano practically never erupts, so they're stuck with the two or so boulders that it starts off with) and heavy predation by the ugglies. Eventually, nothing will exist except for a staggering number of blowflies (who manage to get into EVERYTHING).
The jungle terrarium is probably one of the worst. It starts off with such beautiful diversity, and within moments it has all been devoured by those damned burrowing crabs. They eat everything, and there's nothing that eats them (aside from the occasional idiot who somehow manages to fall into the piranha pit when you have it open). And they just seem to spawn new ones from the ground, making it impossible to rid the ship of them.
The only hope is to take the species that mean something to you and relocating them to a different area. Leave the jungle terrarium to the crabs and the mosquitoes.
Also, word of advice... Replicating a kobold = Awesome. They will fight each other for eternity, and they can smack each other quite a fair distance.
The only way I managed to get any semblance of life kicking off was if I hooked up a repeating switch to both the cloud machine and the volcano machine. This would cause a perpetual stream of clouds and hot volcano rocks to spew forth in their respective terrariums. I think I did the same thing with that nutrient-launcher in the aquarium. All of those places had very shaky food chains.
I managed to make a grendel-seeking mud-shooting jet-propelled alarm platform in that game once. Was interesting.