Tierra (computer simulation)
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Tierra is a computer simulation developed by
ecologist Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...
Thomas S. Ray in the early 1990s in which
computer program A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components. A computer program ...
s compete for time (central processing unit ( CPU) time) and space (access to main memory). In this context, the computer programs in Tierra are considered to be evolvable and can
mutate In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitos ...
, self-replicate and recombine. Tierra's virtual machine is written in C. It operates on a custom instruction set designed to facilitate code changes and reordering, including features such as jump to template (as opposed to the relative or absolute jumps common to most instruction sets).


Simulations

The basic Tierra model has been used to experimentally explore '' in silico'' the basic processes of
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
ary and
ecological Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...
dynamics. Processes such as the dynamics of
punctuated equilibrium In evolutionary biology, punctuated equilibrium (also called punctuated equilibria) is a theory that proposes that once a species appears in the fossil record, the population will become stable, showing little evolutionary change for most of i ...
, host-parasite co-evolution and density-dependent
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
are amenable to investigation within the Tierra framework. A notable difference between Tierra and more conventional models of evolutionary computation, such as genetic algorithms, is that there is no explicit, or
exogenous In a variety of contexts, exogeny or exogeneity () is the fact of an action or object originating externally. It contrasts with endogeneity or endogeny, the fact of being influenced within a system. Economics In an economic model, an exogeno ...
fitness function {{no footnotes, date=May 2015 A fitness function is a particular type of objective function that is used to summarise, as a single figure of merit, how close a given design solution is to achieving the set aims. Fitness functions are used in geneti ...
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 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 throu ...
), although this claim has not been realized – like other digital evolution systems, it eventually reaches 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 (often abbreviated ALife or A-Life) is a field of study wherein researchers examine systems related to natural life, its processes, and its evolution, through the use of simulations with computer models, robotics, and biochemistry ...
. Mark Bedau and
Norman Packard Norman Harry Packard (born 1954 in Billings, Montana) 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 f ...
developed a statistical method of classifying evolutionary systems and in 1997, Bedau ''et al.'' applied these statistics to Evita, an
Artificial life Artificial life (often abbreviated ALife or A-Life) is a field of study wherein researchers examine systems related to natural life, its processes, and its evolution, through the use of simulations with computer models, robotics, and biochemistry ...
model similar to Tierra and
Avida Avida is an artificial life software platform to study the evolutionary biology of self-replicating and evolving computer programs ( digital organisms). Avida is under active development by Charles Ofria's Digital Evolution Lab at Michigan Stat ...
, 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 not observed complexity growth in Tierran evolution.Standish, R.K. 2003 "Open-ended artificial evolution", ''International Journal of Computational Intelligence and Applications 3(2)'', 167-175 Tierra is an abstract model, but any quantitative model is still subject to the same validation and verification techniques applied to more traditional mathematical models, and as such, has no special status. The creation of more detailed models in which more realistic dynamics of biological systems and organisms are incorporated is now an active research field (see systems biology).


See also

*
Avida Avida is an artificial life software platform to study the evolutionary biology of self-replicating and evolving computer programs ( digital organisms). Avida is under active development by Charles Ofria's Digital Evolution Lab at Michigan Stat ...
*
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 evolut ...
* Digital organism simulator * Evolutionary computation *
Fitness landscape Fitness may refer to: * Physical fitness, a state of health and well-being of the body * Fitness (biology), an individual's ability to propagate its genes * Fitness (cereal), a brand of breakfast cereals and granola bars * ''Fitness'' (magazine), ...


References


Further reading

* Bentley, Peter, J. 2001, "Digital Biology:How Nature is transforming Our Technology and Our Lives", Simon & Schuster, New York, NY. Previously published in Great Britain in 2001 by Headline Book Publishing. * 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


External links


Tierra home page
{{DEFAULTSORT:Tierra (Computer Simulation) Artificial life Artificial life models Digital organisms