It’s starting to get interesting. In the last few weeks the little critters have acquired some digital genetic code and simple ANN-based brains.

TL;DR The intriguing bit about all of this is that AI, body shape and brain are bred via artificial natural selection - for want of a better name. Practically all observed behaviour is emergent.

Here’s how the simulation works.


There are 3 types of agents in the world:

Resources and Emitters.

  • Resources look like little triangles. They spawned at a fixed rate by Emitters.
  • Their lifespan is very short and their only purpose is to provide nourishment for the Minions.
  • Minions can detect nearby Resources with their sensor, and detect the nearest Emitters at any distance.


These are the little rustoid critters.

  • Each Minion shape and behaviour is determined by its, practically unique, genotype, which is basically just a string of bits.
  • Body plan, limb geometry and mass distribution are fully simulated via the box2d physics engine.
  • Body plan, gender, appearance, and brain aspects of the phenotype of each Minion are fully determined by its genetic code.
  • Each Minion’s brain is implemented via a simple 3 layer neural network. Brain has no learning capabilities, all behaviour is hardcoded at birth by genotype alone.
  • Each Minion has a sensor to detect nearby Resources and the nearest Emitter, among other variables.
  • Up to 4 inputs from the sensor determine the outputs of the brain which enable actuators if their value exceed certain personality-dependent thresholds. Left and right rudders which exert pull, thrusters push, and a linear brake reduces forward speed.
  • Each action by a Minion, including waiting idle and reproducing, consumes a certain amount of energy. When energy is depleted, the Minion dies and some of its body is released back as Resources.
  • Minions who eat resources can top-up their energy pool, survive longer and reproduce via spores.
  • Minions who are unsuccessful at finding and eating food will not leave offspring driving their lineage extinct.


  • The little 5-lobed balls produced by the Minions by means of which they reproduce.
  • During reproduction, the genotype is transmitted but the process introduces a variable number of mutations. Each mutation flips a random bit of the genotype.
  • After a short time, Spores hatch into Minions.
  • If an unfertilized Spore is touched by a Minion of a different gender, of which there are four, it acquires its genetic material and the resulting Minion will have a gene which is a crossover of the two.

I’m still trying to figure out what kind of gameplay can be built out of the emergent mechanics.

Try it

Visit the GitHub project, or, if you’re in a hurry:

git clone && cd rust-oids && cargo run --release

Published September 17, 2016