Change the sliders, which simulates whatever traits in an environment best helps it survive and reproduce. Scratch cat cells have more chance of dying based on how far away their traits are from the optimal trait-range (see Instructions). If they reproduce, mutations can occur. Those with best mutations have best chance of reproducing. The overall result is for you to see.
Credit to Charles Darwin and his book "On the Origin of a Species" Credit to my 5th-8th grade science teachers for introducing to me evolution.
