Q4.1: What about Alife systems, like Tierra and VENUS?

None of these are EVOLUTIONARY ALGORITHMs, but all of them use the evolutionary metaphor as their "playing field".


Synthetic organisms have been created based on a computer metaphor of organic life in which CPU time is the ``energy'' resource and memory is the ``material'' resource. Memory is organized into informational patterns that exploit CPU time for self-replication. MUTATION generates new forms, and EVOLUTION proceeds by natural SELECTION as different GENOTYPEs compete for CPU time and memory space.

Observation of nature shows that evolution by natural selection is capable of both OPTIMIZATION and creativity. Artificial models of evolution have demonstrated the optimizing ability of evolution, as exemplified by the field of GENETIC ALGORITHMs. The creative aspects of evolution have been more elusive to model. The difficulty derives in part from a tendency of models to specify the meaning of the ``genome'' of the evolving entities, precluding new meanings from emerging. I will present a natural model of evolution demonstrating both optimization and creativity, in which the GENOME consists of sequences of executable machine code.

From a single rudimentary ancestral ``creature'', very quickly there evolve parasites, which are not able to replicate in isolation because they lack a large portion of the genome. However, these parasites search for the missing information, and if they locate it in a nearby creature, parasitize the information from the neighboring genome, thereby effecting their own replication.

In some runs, hosts evolve immunity to attack by parasites. When immune hosts appear, they often increase in frequency, devastating the parasite POPULATIONs. In some runs where the community comes to be dominated by immune hosts, parasites evolve that are resistant to immunity.

Hosts sometimes evolve a response to parasites that goes beyond immunity, to actual (facultative) hyper-parasitism. The hyper-parasite deceives the parasite causing the parasite to devote its energetic resources to replication of the hyper-parastie genome. This drives the parasites to extinction. Evolving in the absence of parasites, hyper-parasites completely dominate the community, resulting in a relatively uniform community characterized by a high degree of relationship between INDIVIDUALs. Under these circumstances, sociality evolves, in the form of creatures which can only replicate in aggregations.

The cooperative behavior of the social hyper-parasites makes them vulnerable to a new class of parasites. These cheaters, hyper-hyper-parasites, insert themselves between cooperating social individuals, deceiving the social creatures, causing them to replicate the genomes of the cheaters.

The only genetic change imposed on the simulator is random bit flips in the machine code of the creatures. However, it turns out that parasites are very sloppy replicators. They cause significant RECOMBINATION and rearrangement of the genomes. This spontaneous sexuality is a powerful force for evolutionary change in the system.

One of the most interesting aspects of this instance of life is that the bulk of the evolution is based on adaptation to the biotic ENVIRONMENT rather than the physical environment. It is co-evolution that drives the system.

--- "Tierra announcement" by Tom Ray (1991)

How to get Tierra?

Tierra is available (source and executables, for Unix and NT) from ftp://alife.santafe.edu/pub/SOFTWARE/Tierra .

Related work

David Bennett <dmb@pfxcorp.com> reported in March 2000: Much new work has been done in Tierra since 1993. Thomas Ray <tray@mail.nhn.ou.edu> is now working in Japan. I have been using another similar system called Avida. It has some advantages, and a significant body of research results. The contact for Avida is <avida@krl.caltech.edu>.


Ray, T. S. (1991) "Is it alive, or is it GA?" in [ICGA91], 527--534.

Ray, T. S. (1991) "An approach to the synthesis of life." in [ALIFEII], 371--408.

Ray, T. S. (1991) "Population dynamics of digital organisms." in [ALIFEII].

Ray, T. S. (1991) "Evolution and optimization of digital organisms." Scientific Excellence in Supercomputing: The IBM 1990 Contest Prize Papers, Eds. Keith R. Billingsley, Ed Derohanes, Hilton Brown, III. Athens, GA, 30602, The Baldwin Press, The University of Georgia.

Ray, T. S. (1992) "Evolution, ecology and optimization of digital organisms." Santa Fe Institute working paper 92-08-042.

Ray, T. S. "Evolution, complexity, entropy, and artificial reality." submitted Physica D.

Ray, T. S. (1993) "An evolutionary approach to synthetic biology, Zen and the art of creating life. Artificial Life 1(1).


Steen Rasmussen's (et al.) VENUS I+II "coreworlds" as described in [ALIFEII] and [LEVY92], are inspired by A.K. Dewdney's well-known article (Dewdney 1984). Dewdney proposed a game called "Core Wars", in which hackers create computer programs that battle for control of a computer's "core" memory (Strack 93). Since computer programs are just patterns of information, a successful program in core wars is one that replicates its pattern within the memory, so that eventually most of the memory contains its pattern rather than that of the competing program.

VENUS is a modification of Core Wars in which the Computer programs can mutate, thus the pseudo assembler code creatures of VENUS evolve steadily. Furthermore each memory location is endowed with "resources" which, like sunshine are added at a steady state. A program must have sufficient resources in the regions of memory it occupies in order to execute. The input of resources determines whether the VENUS ecosystem is a "jungle" or a "desert." In jungle ENVIRONMENTs, Rasmussen et al. observe the spontaneous emergence of primitive "copy/split" organisms starting from (structured) random initial conditions.

--- [ALIFEII], p.821

Dewdney, A.K. (1984) "Computer Recreations: In the Game called Core War Hostile Programs Engage in a Battle of Bits", Sci. Amer. 250(5), 14-22.

Farmer & Belin (1992) "Artificial Life: The Coming Evolution", [ALIFEII], 815-840.

Rasmussen, et al. (1990) "The Coreworld: Emergence and Evolution of Cooperative Structures in a Computational Chemistry", [FORREST90], 111-134.

Rasmussen, et al. (1992) "Dynamics of Programmable Matter", [ALIFEII], 211-254.

Strack (1993) "Core War Frequently Asked Questions ( rec.games.corewar FAQ)" Avail. by anon. FTP from ftp://rtfm.mit.edu/pub/usenet/news.answers/games/corewar-faq.Z


Larry Yaeger's PolyWorld as described in [ALIFEIII] and [LEVY92] is available via anonymous FTP from ftp://alife.santafe.edu/pub/SOFTWARE/Polyworld/

"The subdirectories in this "polyworld" area contain the source code for the PolyWorld ecological simulator, designed and written by Larry Yaeger, and Copyright 1990, 1991, 1992 by Apple Computer.

PostScript versions of my ARTIFICIAL LIFE III technical paper have now been added to the directory. These should be directly printable from most machines. Because some unix systems' "lpr" commands cannot handle very large files (ours at least), I have split the paper into Yaeger.ALife3.1.ps and Yaeger.ALife3.2.ps. These files can be ftp-ed in "ascii" mode. For unix users I have also included compressed versions of both these files (indicated by the .Z suffix), but have left the uncompressed versions around for people connecting from non-unix systems. I have not generated PostScript versions of the images, because they are color and the resulting files are much too large to store, retrieve, or print. Accordingly, though I have removed a Word-formatted version of the textual body of the paper that used to be here, I have left a Word-formatted version of the color images. If you wish to acquire it, you will need to use the binary transfer mode to move it to first your unix host and then to a Macintosh (unless Word on a PC can read it - I don't know), and you may need to do something nasty like use ResEdit to set the file type and creator to match those of a standard Word document (Type = WDBN, Creator = MSWD). [..]"

--- from the README by Larry Yaeger <larryy@apple.com>

General Alife repositories?

Also, all of the following FTP sites carry ALIFE related info:

ftp://ftp.cognet.ucla.edu/pub/alife/ , ftp://life.anu.edu.au/pub/complex_systems/alife/ , ftp://ftp.cogs.susx.ac.uk/pub/reports/csrp/ , ftp://xyz.lanl.gov/nlin-sys/ , ftp://alife.santafe.edu/pub/ .

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Hitch Hiker's Guide to Evolutionary Computation, Issue 9.1, released 12 April 2001
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