LIT Creature Forge

Watch creatures invent themselves.

LIT Creature Forge is an evolution simulator based on Karl Sims' 1994 paper "Evolving Virtual Creatures."

Start an evolution and see random segments evolve. The ones that move farthest reproduce, with mutations. Run another generation. Repeat until something organic crawls out of the chaos.

Starting with V1.1, there are now also swimmers, and creatures fighting over the possession of a cube.

There is no design tool. There is no creature editor. Bodies, sensors, brains, and gaits all evolve together without any human input.

What you'll see

Body plans that lurch, hop, tumble, slither, and occasionally do something physically reasonable.

Gaits that develop personality. A cautious shuffle here, a casually-swinging trot there.

Asymmetric creatures that shouldn't work but absolutely do. Quadrupeds with their rear legs attached to their head, bipeds that lean into a permanent forward fall.

Champions that emerge over a few hundred generations and look like deliberately-designed animals (they aren't)

Why this version

The 1994 paper has been replicated many times. Most replications either run on stiffer physics solvers that produce visibly robotic motion, live in academic codebases not meant for hands-on use, or skip the genetic-programming controllers in favor of simpler oscillators.

LIT Creature Forge is a Sims-faithful recreation built on MuJoCo (modern constraint physics). The result reads as organic motion. Just creatures moving the way creatures move.

Tunable, not over-engineered

Population size, trial duration, gravity. Adjust and watch what evolves differently.

Lower gravity opens up jumpers, rollers, and ballistic-phase gaits; higher gravity rewards stable grounded walkers.

Save any champion and replay them in an isolated showcase arena with free camera, for footage, for showing friends, or just to watch your favorite creature trot indefinitely.

No tutorial-driven progression, no "unlock new biomes." It's a sandbox. You watch evolution.

What this isn't

Not a creature designer. (You don't make the creatures. Evolution does.)

Not a goal-based game with progression or winning conditions.

Not realistic biology. Sims-style evolution is dramatic, weird, and indifferent to whether limbs make anatomical sense.

Not a research tool.

The 1994 thesis, delivered with 2026 fluidity

The original paper produced creatures that walked, swam, fought, jumped, and looked alive. Modern hobbyist replications mostly hit the same emergent diversity. What's been hard is producing creatures that look organic, not just kinematically valid. LIT Creature Forge targets that gap.

While this is 1.0, I am planning many more features

However, I didn't want to put it as Early Access, as it's a fully featured software as-is, and with my health, I'm not sure when/if new features will be implemented.

The price has been accounted for that. It will increase as more features are added.

What I have planned is implementing Sims' original swimming simulation as well, along with creatures outright battling each other, jumping fitness etc.

The possibilities are endless, my health is unfortunately not, so I can't overpromise. So I've priced it as is for now, with no more promises. Only hopes.