Darwin's critters is a simulation program of life and evolution.
The critters are small circles. Their DNA gives them capacities like, for instance, by able to capture the light to transform it into energy.
They can use energy to live longer or to move, to reproduce...
During reproduction, the critter is divided in 2 or more. Each new critter receives the DNA of its parent but the DNA may be mutated.
At random mutations, the critter can receive new abilities.