| dc.description.abstract | The central goal of this thesis is to provide additional criteria towards implementing open-ended evolution in an artificial system. Methods inspired by biological evolution are frequently applied to generate autonomous agents too complex to design by hand. Despite substantial progress in the area of evolutionary computation, additional efforts are needed to identify a coherent set of requirements for a system
capable of exhibiting open-ended evolutionary dynamics.
The thesis provides an extensive discussion of existing models and of the major
considerations for designing a computational model of evolution by natural selection.
Thus, the work in this thesis constitutes a further step towards determining
the requirements for such a system and introduces a concrete implementation of
an artificial evolution system to evaluate the developed suggestions. The proposed
system improves upon existing models with respect to easy interpretability of agent
behaviour, high structural freedom, and a low-level sensor and effector model to
allow numerous long-term evolutionary gradients.
In a series of experiments, the evolutionary dynamics of the system are examined
against the set objectives and, where appropriate, compared with existing systems.
Typical agent behaviours are introduced to convey a general overview of the system
dynamics. These behaviours are related to properties of the respective agent populations and their evolved morphologies. It is shown that an intuitive classification of observed behaviours coincides with a more formal classification based on morphology.
The evolutionary dynamics of the system are evaluated and shown to be unbounded according to the classification provided by Bedau and Packard’s measures of evolutionary
activity. Further, it is analysed how observed behavioural complexity relates
to the complexity of the agent-side mechanisms subserving these behaviours. It is
shown that for the concrete definition of complexity applied, the average complexity
continually increases for extended periods of evolutionary time. In combination,
these two findings show how the observed behaviours are the result of an ongoing
and lasting adaptive evolutionary process as opposed to being artifacts of the seeding
process.
Finally, the effect of variation in the system on the diversity of evolved behaviour is investigated. It is shown that coupling individual survival and reproductive success
can restrict the available evolutionary trajectories in more than the trivial sense of removing another dimension, and conversely, decoupling individual survival from reproductive success can increase the number of evolutionary trajectories. The effect of different reproductive mechanisms is contrasted with that of variation in environmental conditions. The diversity of evolved strategies turns out to be sensitive to the reproductive mechanism while being remarkably robust to the variation of environmental conditions. These findings emphasize the importance of being explicit
about the abstractions and assumptions underlying an artificial evolution system,
particularly if the system is intended to model aspects of biological evolution. | en |
