39,432 research outputs found
On Complexity and Emergence
Numerous definitions for complexity have been proposed over the last half
century, with little consensus achieved on how to use the term. A definition of
complexity is supplied here that is closely related to the Kolmogorov
Complexity and Shannon Entropy measures widely used as complexity measures, yet
addresses a number of concerns raised against these measures. However, the
price of doing this is to introduce context dependence into the definition of
complexity. It is argued that such context dependence is an inherent property
of complexity, and related concepts such as entropy and emergence. Scientists
are uncomfortable with such context dependence, which smacks of subjectivity,
and this is perhaps the reason why little agreement has been found on the
meaning of these terms.Comment: submitted to Complexity Internationa
Evolution in the Multiverse
In the {\em Many Worlds Interpretation} of quantum mechanics, the range of
possible worlds (or histories) provides variation, and the Anthropic Principle
is a selective principle analogous to natural selection. When looked on in this
way, the ``process'' by which the laws and constants of physics is determined
not too different from the process that gave rise to our current biodiversity,
i.e. Darwinian evolution. This has implications for the fields of SETI and
Artificial Life, which are based on a philosophy of the inevitability of life.Comment: 4 pages; submitted to Complexity International
(http://www.csu.edu.au/ci/ci.html
Some Techniques for the Measurement of Complexity in Tierra
Recently, Adami and coworkers have been able to measure the information
content of digital organisms living in their {\em Avida} artificial life
system. They show that over time, the organisms behave like Maxwell's demon,
accreting information (or complexity) as they evolve. In {\em Avida} the
organisms don't interact with each other, merely reproduce at a particular rate
(their fitness), and attempt to evaluate an externally given arithmetic
function in order win bonus fitness points. Measuring the information content
of a digital organism is essentially a process of counting the number of
genotypes that give rise to the same phenotype.
Whilst Avidan organisms have a particularly simple phenotype, Tierran
organisms interact with each other, giving rise to an ecology of phenotypes. In
this paper, I discuss techniques for comparing pairs of Tierran organisms to
determine if they are phenotypically equivalent. I then discuss a method for
computing an estimate of the number of phenotypically equivalent genotypes that
is more accurate than the ``hot site'' estimate used by Adami's group. Finally,
I report on an experimental analysis of a Tierra run.Comment: 5 pages; 1 figure; European Conference on Artificial Lif
The Role of Innovation within Economics
This paper discusses dynamic evolutionary economics, and introduces a model
of such.Comment: 20 pages; 5 figure
An Ecolab Perspective on the Bedau Evolutionary Statistics
At Alife VI, Mark Bedau proposed some evolutionary statistics as a means of
classifying different evolutionary systems. Ecolab, whilst not an artificial
life system, is a model of an evolving ecology that has advantages of
mathematical tractability and computational simplicity. The Bedau statistics
are well defined for Ecolab, and this paper reports statistics measured for
typical Ecolab runs, as a function of mutation rate. The behaviour ranges from
class 1 (when mutation is switched off), through class 3 at intermediate
mutation rates (corresponding to scale free dynamics) to class 2 at high
mutation rates. The class 3/class 2 transition corresponds to an error
threshold. Class 4 behaviour, which is typified by the Biosphere, is
characterised by unbounded growth in diversity. It turns out that Ecolab is
governed by an inverse relationship between diversity and connectivity, which
also seems likely of the Biosphere. In Ecolab, the mutation operator is
conservative with respect to connectivity, which explains the boundedness of
diversity. The only way to get class 4 behaviour in Ecolab is to develop an
evolutionary dynamics that reduces connectivity of time.Comment: 5 pages; 3 figures; accepted for Artificial Life VI
Network Complexity of Foodwebs
In previous work, I have developed an information theoretic complexity
measure of networks. When applied to several real world food webs, there is a
distinct difference in complexity between the real food web, and randomised
control networks obtained by shuffling the network links. One hypothesis is
that this complexity surplus represents information captured by the
evolutionary process that generated the network. In this paper, I test this
idea by applying the same complexity measure to several well-known artificial
life models that exhibit ecological networks: Tierra, EcoLab and Webworld.
Contrary to what was found in real networks, the artificial life generated
foodwebs had little information difference between itself and randomly shuffled
versions
Ecolab, Webworld and self-organisation
Ecolab and Webworld are both models of evolution produced by adding evolution
to ecological equations. They differ primarily in the form of the ecological
equations. Both models are self-organised to a state where extinctions balance
speciations. However, Ecolab shows evidence of this self-organised state being
critical, whereas Webworld does not. This paper examines the self-organised
states of these two models and suggest the likely cause of the difference. Also
the lifetime distribution for a mean field version of Ecolab is computed,
showing that the fat tail of the distribution is due to coevolutionary adaption
of the species.Comment: Accepted for Artificial Life IX. Final M
The influence of parsimony and randomness on complexity growth in Tierra
The issue of how to create open-ended evolution in an artificial system is
one the open problems in artificial life. This paper examines two of the
factors that have some bearing on this issue, using the Tierra artificial life
system.
{\em Parsimony pressure} is a tendency to penalise more complex organisms by
the extra cost needed to reproduce longer genotypes, encouraging simplification
to happen. In Tierra, parsimony is controlled by the \verb+SlicePow+ parameter.
When full parsimony is selected, evolution optimises the ancestral organism to
produce extremely simple organisms. With parsimony completely relaxed,
organisms grow larger, but not more complex. They fill up with ``junk''. This
paper looks at scanning a range of \verb+SlicePow+ from 0.9 to 1 to see if
there is an optimal value for generating complexity.
Tierra (along with most ALife systems) use pseudo random number generators.
Algorithms can never create information, only destroy it. So the total
complexity of the Tierra system is bounded by the initial complexity, implying
that the individual organism complexity is bounded. Biological systems,
however, have plenty of sources of randomness, ultimately dependent on quantum
randomness, so do not have this complexity limit. Sources of real random
numbers exist for computers called {\em entropy gatherers} -- this paper
reports on the effect of changing Tierra's pseudo random number generator for
an entropy gatherer
Diversity Evolution
Bedau has developed a general set of evolutionary statistics that quantify
the adaptive component of evolutionary processes. On the basis of these
measures, he has proposed a set of 4 classes of evolutionary system. All
artificial life sytems so far looked at fall into the first 3 classes, whereas
the biosphere, and possibly the human economy belongs to the 4th class. The
challenge to the artificial life community is to identify exactly what is
difference between these natural evolutionary systems, and existing artificial
life systems. At ALife VII, I presented a study using an artificial
evolutionary ecology called \EcoLab. Bedau's statistics captured the
qualitative behaviour of the model. \EcoLab{} exhibited behaviour from the
first 3 classes, but not class 4, which is characterised by unbounded growth in
diversity. \EcoLab{} exhibits a critical surface given by an inverse
relationship between connectivity and diversity, above which the model cannot
tarry long. Thus in order to get unbounded diversity increase, there needs to
be a corresponding connectivity reducing (or food web pruning) process. This
paper reexamines this question in light of two possible processes that reduce
ecosystem connectivity: a tendency for specialisation and increase in
biogeographic zones through continental drift
Going Stupid with EcoLab
In 2005, Railsback et al. proposed a very simple model ({\em Stupid
Model}) that could be implemented within a couple of hours, and later
extended to demonstrate the use of common ABM platform functionality. They
provided implementations of the model in several agent based modelling
platforms, and compared the platforms for ease of implementation of this simple
model, and performance. In this paper, I implement Railsback et al's Stupid
Model in the EcoLab simulation platform, a C++ based modelling platform,
demonstrating that it is a feasible platform for these sorts of models, and
compare the performance of the implementation with Repast, Mason and Swarm
versions
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