This is an edited version of the FAQ (Frequently Asked Questions) from the comp.ai.alife newsgroup.

For the original version, go to http://www-2.cs.cmu.edu/afs/cs.cmu.edu/project/ai-repository/ai/html/faqs/ai/alife/faq-doc-2.html

Biology is the scientific study of life - in principle, anyway. In practice, biology is the scientific study of life on Earth based on carbon-chain chemistry. There is nothing in its charter that restricts biology to carbon-based life; it is simply that this is the only kind of life that has been available to study. Thus, theoretical biology has long faced the fundamental obstacle that it is impossible to derive general principles from single examples.

Without other examples, it is difficult to distinguish essential properties of life - properties that would be shared by any living system - from properties that may be incidental to life in principle, but which happen to be universal to life on Earth due solely to a combination of local historical accident and common genetic descent.

In order to derive general theories about life, we need an ensemble of instances to generalize over. Since it is quite unlikely that alien lifeforms will present themselves to us for study in the near future, our only option is to try to create alternative life-forms ourselves - Artificial Life - literally "life made by Man rather than by Nature."

Artificial Life ("AL" or "Alife") is the name given to a new discipline that studies "natural" life by attempting to recreate biological phenomena from scratch within computers and other "artificial" media. Alife complements the traditional analytic approach of traditional biology with a synthetic approach in which, rather than studying biological phenomena by taking apart living organisms to see how they work, one attempts to put together systems that behave like living organisms.

The process of synthesis has been an extremely important tool in many disciplines. Synthetic chemistry - the ability to put together new chemical compounds not found in nature - has not only contributed enormously to our theoretical understanding of chemical phenomena, but has also allowed us to fabricate new materials and chemicals that are of great practical use for industry and technology.

Artificial life amounts to the practice of "synthetic biology" and, by analogy with synthetic chemistry, the attempt to recreate biological phenomena in alternative media will result in not only better theoretical understanding of the phenomena under study, but also in practical applications of biological principles in the technology of computer hardware and software, mobile robots, spacecraft, medicine, nanotechnology, industrial fabrication and assembly, and other vital engineering projects.

By extending the horizons of empirical research in biology beyond the territory currently circumscribed by life-as-we-know-it, the study of Artificial Life gives us access to the domain of life-as-it- could-be, and it is within this vastly larger domain that we must ground general theories of biology and in which we will discover practical and useful applications of biology in our engineering endeavors.

-- Chris G. Langton

There are several "popular science" books out there. _Artificial Life: the Quest for a New Creation_, by Steven Levy, was one of the first; Levy presents a large amount of material detailing the genesis of the field, including a description of many still-active projects. This would be my first recommendation for a newcomer.

There is a World-Wide-Web page for this book at the URL http://mosaic.echonyc.com/~steven/ArtificialLife.html.

M. Mitchell Waldrop's _Complexity: The Emerging Science at the Edge of Order and Chaos_ (ISBN 0-671-76789-5) discusses the history of complex systems study. In specific, it details the founding of the Santa Fe Institute, which is actively researching most aspects of complex systems, including Artificial Life.

Rudy Rucker's _Artificial Life Lab_ has been recommended as a good way to get involved; I haven't yet read it.

Finally, the book _Out of Control_ by Kevin Kelly is reputed to be a good 1994 overview of technology, with an emphasis on emergent behavior and modelling life in a computer environment.

Apart from the list [ below ] which contains references to programs and demos which have often been requested on the newsgroup, the best way to find something specific is to ask on the newsgroup! Even if the people from the particular project don't actually read the newsgroup, someone who knows them probably does...

How do I find:

• Tierra

  The complete source code and documentation (NOT the executables) for Tom Ray's tierra program are available via anonymous FTP at:

       ftp://tierra.slhs.udel.edu [ 128.175.41.34 ] and
       ftp://life.slhs.udel.edu [ 128.185.41.33 ]

  in the directory /tierra, file tierra.tar.Z.

• Karl Sim's movie (from the ALIFE IV conference)

  Karl Sim's movie, presented at the ALIFE IV conference, is available via FTP at:

       ftp://ftp.think.com/users/karl/creatures-demo.mpg  [ BROKEN ]

There is a connection between the two fields in both methodology and research. AI is much older, with conceptual work dating to 1950 and beyond, while AL coagulated in the late 1980s, when people recognized similarities in the work they were doing. AI methodologies play a large part in AL work, partly because of the recognizable similarities in the two disciplines: AI studying intelligence, AL studying life, both with an eye to usefulness and reproducibility. And, in recent years, "traditional" AI researchers have focussed on AL techniques for autonomous learning, among other things.

In spite of these similarities, there are several dissimilarities. AL is grounded in biology, physics, chemistry and mathematics, while AI is pursued mainly by computer scientists, engineers, and psychologists. Also, the general philosophy of researchers in the fields seems to approach similar problems from different sides; AL from the ground up, in an attempt to study synthesis, AI from the top down, focussing on results and not implementation.

[ The text above is my opinion; I welcome alternative viewpoints on the subject, of course. --Titus ]

Titus Brown, brown@krl.caltech.edu.