Tierra (computer simulation)
Encyclopedia
Tierra is a computer simulation
developed by ecologist Thomas S. Ray
in the early 1990s in which computer program
s compete for central processing unit (CPU
) time and access to main memory. At present, the commonly accepted definition of life does not consider any computer program to be alive, however, Tierra is an example of an artificial life
model; in the metaphor of the Tierra, the evolvable computer programs can be considered as digital organism
s which compete for energy (CPU time) and resources (main memory). In this context, the computer programs in Tierra could be considered evolvable
and can mutate
, self-replicate
and recombine
.
the basic processes of evolution
ary and ecological
dynamics. Processes such as the dynamics of punctuated equilibrium
, host
-parasite co-evolution
and density-dependent natural selection
are amenable to investigation within the Tierra framework. A notable difference to more conventional models of evolutionary computation
, such as genetic algorithm
s is that there is no explicit, or exogenous fitness function
built into the model. Often in such models there is the notion of a function being "optimized"; in the case of Tierra, the fitness function is endogenous: there is simply survival and death.
According to Thomas S. Ray and others, this may allow for more "open-ended" evolution, in which the dynamics of the feedback between evolutionary and ecological processes can itself change over time (see evolvability
) although this claim has not been realized – like other digital evolution systems, it eventually comes to a point where novelty ceases to be created, and the system at large begins either looping or ceases to 'evolve'. The issue of how true open-ended evolution can be implemented in an artificial system is still an open question in the field of Artificial life
.
Mark Bedau
and Norman Packard
developed statistical method of classifying evolutionary systems and in 1997, Bedau et al. applied these statistics to Evita, an Artificial life
model similar to Tierra and Avida
, but with limited organism interaction, and no parasitism, and concluded that Tierra-like systems do not exhibit the open-ended evolutionary signatures of naturally evolving systems.
Russell K. Standish
has measured the informational complexity of Tierran 'organisms', and has similarly found limited complexity growth in Tierran evolution.
Tierra is an abstract model, but any quantitative model is still subject to the same validation and verification techniques applied to more traditional mathematical model
s, and as such, has no special status. More detailed models in which more realistic dynamics of biological systems and organisms are incorporated is now an active research field (see systems biology
).
Computer simulation
A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...
developed by ecologist Thomas S. Ray
Thomas S. Ray
Thomas S. Ray is an ecologist who created and developed the Tierra project, a computer simulation of artificial life.In 1975, he and Donald R...
in the early 1990s in which computer program
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
s compete for central processing unit (CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
) time and access to main memory. At present, the commonly accepted definition of life does not consider any computer program to be alive, however, Tierra is an example of an artificial life
Artificial life
Artificial life is a field of study and an associated art form which examine systems related to life, its processes, and its evolution through simulations using computer models, robotics, and biochemistry. The discipline was named by Christopher Langton, an American computer scientist, in 1986...
model; in the metaphor of the Tierra, the evolvable computer programs can be considered as digital organism
Digital organism
A digital organism is a self-replicating computer program that mutates and evolves. Digital organisms are used as a tool to study the dynamics of Darwinian evolution, and to test or verify specific hypotheses or mathematical models of evolution...
s which compete for energy (CPU time) and resources (main memory). In this context, the computer programs in Tierra could be considered evolvable
Evolvability
Evolvability is defined as the capacity of a system for adaptive evolution. Evolvability is the ability of a population of organisms to not merely generate genetic diversity, but to generate adaptive genetic diversity, and thereby evolve through natural selection.In order for a biological organism...
and can mutate
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
, self-replicate
Self-replication
Self-replication is any behavior of a dynamical system that yields construction of an identical copy of that dynamical system. Biological cells, given suitable environments, reproduce by cell division. During cell division, DNA is replicated and can be transmitted to offspring during reproduction...
and recombine
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
.
Simulations
The basic Tierra model has been used to experimentally explore in silicoIn silico
In silico is an expression used to mean "performed on computer or via computer simulation." The phrase was coined in 1989 as an analogy to the Latin phrases in vivo and in vitro which are commonly used in biology and refer to experiments done in living organisms and outside of living organisms,...
the basic processes of evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary and ecological
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
dynamics. Processes such as the dynamics of punctuated equilibrium
Punctuated equilibrium
Punctuated equilibrium is a theory in evolutionary biology which proposes that most species will exhibit little net evolutionary change for most of their geological history, remaining in an extended state called stasis...
, host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
-parasite co-evolution
Co-evolution
In biology, coevolution is "the change of a biological object triggered by the change of a related object." Coevolution can occur at many biological levels: it can be as microscopic as correlated mutations between amino acids in a protein, or as macroscopic as covarying traits between different...
and density-dependent natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
are amenable to investigation within the Tierra framework. A notable difference to more conventional models of evolutionary computation
Evolutionary computation
In computer science, evolutionary computation is a subfield of artificial intelligence that involves combinatorial optimization problems....
, such as genetic algorithm
Genetic algorithm
A genetic algorithm is a search heuristic that mimics the process of natural evolution. This heuristic is routinely used to generate useful solutions to optimization and search problems...
s is that there is no explicit, or exogenous fitness function
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
built into the model. Often in such models there is the notion of a function being "optimized"; in the case of Tierra, the fitness function is endogenous: there is simply survival and death.
According to Thomas S. Ray and others, this may allow for more "open-ended" evolution, in which the dynamics of the feedback between evolutionary and ecological processes can itself change over time (see evolvability
Evolvability
Evolvability is defined as the capacity of a system for adaptive evolution. Evolvability is the ability of a population of organisms to not merely generate genetic diversity, but to generate adaptive genetic diversity, and thereby evolve through natural selection.In order for a biological organism...
) although this claim has not been realized – like other digital evolution systems, it eventually comes to a point where novelty ceases to be created, and the system at large begins either looping or ceases to 'evolve'. The issue of how true open-ended evolution can be implemented in an artificial system is still an open question in the field of Artificial life
Artificial life
Artificial life is a field of study and an associated art form which examine systems related to life, its processes, and its evolution through simulations using computer models, robotics, and biochemistry. The discipline was named by Christopher Langton, an American computer scientist, in 1986...
.
Mark Bedau
Mark Bedau
Mark A. Bedau is an American philosopher who works in the field of Artificial Life. He is the son of philosopher Hugo Adam Bedau.Bedau teaches philosophy at Reed College. He is also the Co-Founder of the European Center for Living Technology and Visiting Professor, Ph.D. Program in Life Sciences:...
and Norman Packard
Norman Packard
Norman Harry Packard is a chaos theory physicist and one of the founders of the Prediction Company and ProtoLife. He is an alumnus of Reed College and the University of California, Santa Cruz. Packard is known for his contributions to both chaos theory and cellular automata...
developed statistical method of classifying evolutionary systems and in 1997, Bedau et al. applied these statistics to Evita, an Artificial life
Artificial life
Artificial life is a field of study and an associated art form which examine systems related to life, its processes, and its evolution through simulations using computer models, robotics, and biochemistry. The discipline was named by Christopher Langton, an American computer scientist, in 1986...
model similar to Tierra and Avida
Avida
Avida is an artificial life software platform to study the evolutionary biology of self-replicating and evolving computer programs . Avida is under active development by Charles Ofria's Digital Evolution Lab at Michigan State University and was originally designed by Ofria, Chris Adami and C. Titus...
, but with limited organism interaction, and no parasitism, and concluded that Tierra-like systems do not exhibit the open-ended evolutionary signatures of naturally evolving systems.
Russell K. Standish
Russell K. Standish
Russell K. Standish is a computational scientist based in Sydney, Australia. He was the founding director of UNSW's from 1997-2005. In 2005 he established a computational science consultancy called . Since 2002, he has held an adjunct associate professorship with UNSW's . He grew up in Western...
has measured the informational complexity of Tierran 'organisms', and has similarly found limited complexity growth in Tierran evolution.
Tierra is an abstract model, but any quantitative model is still subject to the same validation and verification techniques applied to more traditional mathematical model
Mathematical model
A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used not only in the natural sciences and engineering disciplines A mathematical model is a...
s, and as such, has no special status. More detailed models in which more realistic dynamics of biological systems and organisms are incorporated is now an active research field (see systems biology
Systems biology
Systems biology is a term used to describe a number of trends in bioscience research, and a movement which draws on those trends. Proponents describe systems biology as a biology-based inter-disciplinary study field that focuses on complex interactions in biological systems, claiming that it uses...
).
See also
- AvidaAvidaAvida is an artificial life software platform to study the evolutionary biology of self-replicating and evolving computer programs . Avida is under active development by Charles Ofria's Digital Evolution Lab at Michigan State University and was originally designed by Ofria, Chris Adami and C. Titus...
- Core WarCore WarCore War is a programming game in which two or more battle programs compete for the control of the "Memory Array Redcode Simulator" virtual computer . These battle programs are written in an abstract assembly language called Redcode...
- Digital organismDigital organismA digital organism is a self-replicating computer program that mutates and evolves. Digital organisms are used as a tool to study the dynamics of Darwinian evolution, and to test or verify specific hypotheses or mathematical models of evolution...
s - Evolutionary computationEvolutionary computationIn computer science, evolutionary computation is a subfield of artificial intelligence that involves combinatorial optimization problems....
- Fitness landscapeFitness landscapeIn evolutionary biology, fitness landscapes or adaptive landscapes are used to visualize the relationship between genotypes and reproductive success. It is assumed that every genotype has a well-defined replication rate . This fitness is the "height" of the landscape...
- Other Simulators for ALife
- Artificial intelligenceArtificial intelligenceArtificial intelligence is the intelligence of machines and the branch of computer science that aims to create it. AI textbooks define the field as "the study and design of intelligent agents" where an intelligent agent is a system that perceives its environment and takes actions that maximize its...
Additional reading
- Ray, T. S. 1991, "Evolution and optimization of digital organisms", in Billingsley K.R. et al. (eds), Scientific Excellence in Supercomputing: The IBM 1990 Contest Prize Papers, Athens, GA, 30602: The Baldwin Press, The University of Georgia. Publication date: December 1991, pp. 489–531.
- Casti, John L. (1997). Would-Be-Worlds. John Wiley & Sons, Inc. New York ISBN 0-471-12308-0