Thomas S. Ray (currently: Dept. of Zoology, Univ. of Oklahoma) Ecologist and Tropical Biologist.

Ray had been introduced to self-replicating computger code in a virtual machine (Core Wars) by an MIT hacker. Introduced feature of mutation by which code randomly flipped bits when copying data; if that data happened to be machine code for a program, the program mutated. Effects could rapidly be traced through many generations. Beginning of work on Digital Evolution--Evolution by natural selection embedded in "the medium of digital computation."


  • Evolution by natural selection has generated complex and intelligent life forms in the medium of carbon chemistry.
  • Evolution is the only process with a proven ability to produce intelligence.
  • The DNA of living organisms is a genetic ``program''. This is a parallel software of a complexity much greater than any that could be written by humans.
  • Experiments illustrated here show that evolution by natural selection works very effectively in the medium of computer machine code.
  • Evolution will find forms and processes that exploit the possibilities inherent in the computational medium.


  • Self-replicating machine code programs are introduced to the RAM memory of the computer.
  • Genetic variation occurs due to ``mutations'' resulting from random flips (between 0 and 1) of bits in the memory.
  • A ``reaper'' function of the operating system kills old or defective processes in order to make way for newborn programs, once the memory is full.
Hosts, red, are very common. Parasites, yellow, have appeared but are still rare. Immune hosts (blue) are increasing in frequency, separating the parasites into the top of memory.

From: Tom Ray, "Tierra Photoessay," URL: http://www.isd.atr.co.jp/~ray/pubs/images/index.html