From Artificial Evolution to Artificial Life

317 Pages·1999·5.1 MB·English

From Arti(cid:12)cial Evolution to Arti(cid:12)cial Life
Timothy John Taylor
U N IVER
E S
H IT
T Y
O H
G
F
R
E U
DIN B
PhD
University of Edinburgh
1999

To Pete
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Abstract
Thisworkaddressesthequestion: Whatarethebasicdesignconsiderationsforcreating
a synthetic model of the evolution of living systems (i.e. an ‘arti(cid:12)cial life’ system)? It
can also be viewed as an attempt to elucidate the logical structure (in a very general
sense) of biological evolution. However, with no adequate de(cid:12)nition of life, the experi-
mental portion of the work concentrates on more speci(cid:12)c issues, and primarily on the
issue of open-ended evolution. An arti(cid:12)cial evolutionary system called Cosmos, which
provides a virtual operating system capable of simulating the parallel processing and
evolution of a population of several thousand self-reproducing computer programs, is
introduced. Cosmos is related to Ray’s established Tierra system [Ray 91], but there
are a number of signi(cid:12)cant di(cid:11)erences. A wide variety of experiments with Cosmos,
whichweredesignedtoinvestigateitsevolutionarydynamics,arereported. Ananalysis
of the results is presented, with particular attention given to the role of contingency
in determining the outcome of the runs. The results of this work, and consideration of
the existing literature on arti(cid:12)cial evolutionary systems, leads to the conclusion that
arti(cid:12)cial life models such as this are lacking on a number of theoretical and meth-
odological grounds. It is emphasised that explicit theoretical considerations should
guide the design of such models, if they are to be of scienti(cid:12)c value. An analysis of
various issues relating to self-reproduction, especially in the context of evolution, is
presented, including some extensions to von Neumann’s analysis of self-reproduction
[von Neumann 66]. This suggests ways in which the evolutionary potential of such
models might be improved. In particular, a shift of focus is recommended towards a
morecarefulconsiderationofthephenotypiccapabilitiesofthereproducingindividuals.
Phenotypic capabilitiesfundamentally involve interactions withthe environment (both
abiotic and biotic), and it is further argued that the theoretical grounding upon which
these models should be based must include consideration of the kind of environments
and the kind of interactions required for open-ended evolution. A number of useful
future research directions are identi(cid:12)ed. Finally, the relevance of such work to the ori-
ginal goal of modellingthe evolution of living systems (as opposed to the more general
goal of modelling open-ended evolution) is discussed. It is suggested that the study of
open-ended evolution can lead us to a better understanding of the essential properties
of life, but only if the questions being asked in these studies are phrased appropriately.
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Acknowledgements
Many people have contributed in a variety of ways to the productionof this thesis over
the last three and a half years.
First of all, I would like to thank John Hallam, my supervisor. John took me on as
a student, and has always been ready to o(cid:11)er guidance, discussion and constructive
criticism of my work. He has also allowed me the freedom to follow my own academic
interests in the course of my work, which I greatly appreciate. Thanks John!
The interdisciplinarynature of my work has required me to seek advice and discussion
from a wide variety of people. Their generosity in giving up their valuable time to
answer my questions and read drafts of some of the following chapters has consistently
surprised me (especially those whom I know only by email exchanges).
Chiefamongmylistof‘extrasupervisors’isMarkBedaufromReedCollegeintheUSA.
Since (cid:12)rst meeting Mark inearly 1997 at the Philosophyof Arti(cid:12)cialLife conference in
Oxford, he has provided vital encouragement, suggestions and discussion of my work.
From a practical point of view, he also developed a range of analysis and visualisation
techniques for evolutionary systems, which I have used extensively. I would also like to
thank Emile Snyder, who implemented the analysis software and has helped me to use
it. Thanks, Emile, you saved me a lot of time!
Tom Ray read through an early draft of the Cosmos design document, and provided
useful comments and suggestions. The work reported in Section 6.1 was originally
publishedin the proceedings of the Sixth International Conference on Arti(cid:12)cial Life in
1998, and I would like to thank Chris Adami and the four anonymous reviewers who
o(cid:11)eredcommentsontheoriginalpaper. TowardstheendofmyresearchIhavehadsome
invaluable discussions, and comments on drafts of various chapters, from a number of
other people. Iespeciallythank Nick Barton, JohnHolland,Howard Pattee andMoshe
Sipperfor readingand providingusefulcomments on Chapter 7 (and Chapter 2 as well
in Nick Barton’s case). Thanks also to Barry McMullin for providing clari(cid:12)cation on
some issues, and to Daniel Mange for some interesting discussion.
I have had a great time at a number of conferences over the last few years, and these
have been made even more enjoyable by a number of people I’ve met at them. In
particular, thanks to Jason Noble and Alastair Channon|see you at ECAL’99?
During my research I have also bene(cid:12)ted from some much broader discussions about
arti(cid:12)cial life, arti(cid:12)cial intelligence, life, the universe and everything. These discussions
haveoftenbeenlubricatedwithplentyofbeer,andfedwithcopiousamountsofchicken
korma and egg foo yung. I am indebted to the other members of the Mobile Robots
Group in the (former) Department of Arti(cid:12)cial Intelligence, for making it such a fun
placetowork. Inparticular(at theriskofo(cid:11)endingthe others), I’dliketo saya special
thank you to Simon Perkins, Richard Reeve, Arturo Espinosa-Romero, John Demiris,
Nuno Chagas, Sandra Gadanho and Heba Al-Lakany. Thanks also to Judith Good for
the therapeutic moaning sessions about our theses, and to Bernard Go(cid:14)n for putting
up with our constant droning about them during dinners at Teviot.
Therearemanyotherpeopleatthedepartmentwhohavemademylifealoteasier. The
librarians, Olga Franks and Janice Gailani, have always been more than helpful. To
namea few more, KenDawson, Karen Konstro(cid:11)er, Margaret Rennex, DavidWyse and
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Dougie Howie have also been very helpful in a number of ways. I’d also like to thank
the organisers of the EUCS Perl course, for what must be the most useful half-day
course I’ve ever attended.
I would not have been able to conduct this research without the (cid:12)nancial assistance of
a grant from the Engineering and Physical Sciences Research Council (grant number
95306471), for which I am very grateful.
I don’t have enough room to adequately thank my parents for everything they have
done, in so many ways, to enable me to be in the position of submitting this thesis. In
retrospect, it was a Christmasgift from them some years ago of a paperback book|on
theface ofitinsigni(cid:12)cantincomparisonto everythingelsetheyhave doneforme|that
planted the seed for my growing interest in evolution and arti(cid:12)cial life and ultimately
ledme to writethisthesis. ThebookwasThe Blind Watchmaker byRichardDawkins.
Thanks, Mum and Dad, and thanks also to Anne, Katie, Rich and Tamsin.
Of course, it hasn’t all been work over these last three and a half years, and I’d like
to thank those who have kept me away from arti(cid:12)cial life and helped to make my
real life so enjoyable. Apart from various friends already mentioned, thanks to all the
(ex-)Strath(cid:12)llan Road gang|Claudio, Trish, Gordon, Jen, Matt and Wakako. A big
thank you to Simon and O(cid:127)gmundur for all the squash matches and pints in the bar
afterwards|I hope we keep in touch. Thanks also to Stu for the regular and very
welcome co(cid:11)ee breaks, and to Chris and Alan for really taking my mind o(cid:11) work!
But most of all, there is one person who has been with me through every hour of this
time, and without whom I can’t imagine having done this. Thank you Pete, for your
constant love, a(cid:11)ection, friendship and support.
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Declaration
I hereby declare that I composed this thesis entirely myself and that it describes my
own research.
Tim Taylor
Edinburgh
May 29, 1999
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