e-den overview

All atoms have mass (equal to the digit), energy (10 x 2-to-the-power-of-the-digit), colour (arbitrarily represented as 1:white, 2:dark blue, 3:light blue, 4:red, 5:green, 6:yellow, 7:light grey, 8:dark grey and 9:black) and charge (positive or neutral). A simplified physics dictates how these atoms interact. Essentially, no two atoms may occupy the same square: large atoms displace smaller atoms and charged atoms - the organisms - repel neutral atoms. Backround radiation causes one-atoms to appear in empty spaces and then grow along an advancing edge, like grass.

An organism obtains energy by consuming the mass-energy of neighbouring atoms or, less commonly, by killing other organisms. It uses this energy to pay for its metabolic activity. When an organism dies, its atoms lose their charge, the bonds between the atoms break down and an edible corpse of unconnected neutral atoms remains.

Each organism or Bug carries with it a genome, a string of digits, that specifies how it should be constructed (example). A digital genome is typically hundreds or thousands of digits long but can be any length and, in many ways, can be thought of as a small computer program written in a single-purpose language with a robust syntax. Every positive integer represents a legitimate genome. Almost every aspect of the organism, including the sequence of its atoms, the structure and connections of its neurons and its metabolic characteristics, is determined by its genome. When it breeds, the organism passes this genome to its offspring, sometimes with mutations. Bugs may also breed sexually, producing offspring with genomes derived from both parents.

At any one moment, an organism may move, change shape, grow, breed, signal, deposit new atoms, eat or fight. All of these actions are under the organism's voluntary control, with choices dictated by its brain structure, which is in turn determined by its genome. Before making its choices, the organism can study its internal state and its immediate environment, with senses analogous to vision, hearing, hunger and fatigue. Vision is limited to the horizontal and vertical lines extending from each of the organism's 'eyes' (*2 atoms). Hearing enables the organisms to detect the movements of nearby organisms. If wired appropriately, an organism can make sensible decisions on the basis of this information and can exhibit learning and memory.

Bugs can interact with each other by fighting, mating, signalling, feeding each other or by forming mutually beneficial pacts. No organism can occupy the same space as another organism but they can, under some circumstances, touch; the organisms themselves can determine whether close contact between them is safe or whether it should be treated as an episode of conflict to be resolved with the death of the loser. This raises issues of co-operation vs self-interest which the organisms must resolve for themselves at the evolutionary level.

At present, most of these behaviours are potential rather than actual: the e-den program encodes the rules that make such complex behaviour possible but the organisms must have genomes that make sensible use of the rules. Although it is possible to breed the organisms artificially, selecting for desired traits, or even to design the digital genomes directly, it is anticipated that most of the innovation in e-den will ultimately come from Darwinian evolution. The organisms are not scored according to outside criteria: those that succeed are those that best exploit the rules of e-den for their own reproductive ends.

All artificial life programs represent a compromise between competing demands upon the resources of the central processor. If the evolutionary design space or the criteria for determining evolutionary fitness are simple, the design space may be traversed by mutation very quickly; if the design space is complex, or if it takes longer to accept or reject new mutations, then the design space can be explored only slowly. Compared to many other artificial life programs, e-den is complex and evolution is slow. Generation times on a personal computer may proceed over minutes or hours rather than seconds. The potential of e-den, though, is large. The e-den program can be used to create a wide variety of environments ranging from those in which survival and reproduction can be achieved with trivial ease to those in which complex decision making is necessary for survival. Multi-level food-chains are possible, creating evolutionary arms races. Furthermore, by linking computers over the internet, e-den can be used to create a global digital ecosystem of almost unlimited complexity. Furthermore, in its distributed mode, the e-den software could achieve evolutionary progress at an exponentially increased rate.