Biological evolution started from simple components. Much time had passed until the first creatures were able to reproduce. In our artificial world we skip this "chemical evolution" stage. We supply our creatures with basic functions: notation of their features in their genotypes, reproduction, and energy management. We also set the rules of organism building. It would be difficult to simulate a world with quarks, atoms or even proteins as its basic elements. There would be too many of them regarding reasonable size of the artificial world and computational requirements. That is why the basic element of our organisms is much bigger - it is a bar (segment, stick, cylinder...). Such an element can be assigned various functions depending on its genetic description: it can be just a stick, or can transmit and process signals and therefore be a part of a "brain", or be a receptor, or can have "muscles" and cause moves, or can be specialized in supplying energy.
A group of connected sticks makes up an independent organism. It becomes alive when put into the simulator!
Physical simulation module computes interaction of an organism with the world, analyzes forces influencing particular sticks and computes their new positions. The simulation takes place in a three-dimensional space, and uses finite elements theory and rigid bodies dynamics.
Neural module computes excitations in neural nets, collects data from receptors and sends signals to muscles. Organisms' neuron nets are original because of their free topology and inertia of neurons.
Energetic module analyzes gains and looses of energy. An organism can gain energy by assimilation or absorption of food. The work of muscles and neurons means energy looses. After using up all its energy an organism dies.
Creation module creates new organisms by mutating and crossing over genotypes of the best creatures which have lived so far (ancestors). The user can define fitness criterion (by adjusting weights of elementary criterions, like average velocity and average lifespan), which makes direction of evolution possible.