Natural Selection in Biology and on-line
The following idea of evolution by means of natural selection goes back Darwin and Wallace in its original form, who
proposed it as the major mechanism for evolution of living
Three factors are required:
A simple evolutionary algorithm consists in cycling with a
population of creatures through simulations of the effects
of the above factors.
- Offspring are like the parents.
- The offspring may be exactly like a parent, but may
also differ. Sources of variability include mutation and
- Differing Fitness
- The likelihood and number of offspring of a given parent appearing
in the next generation depend on the success of the parent. Success
can be depend on adaptedness to the environment, interaction with
other creatures, luck, and/or other factors.
Reproductive success must
depend (at least in part) on characteristics inherited from
In nature, finiteness of the
environment and of resources are major factors in yielding differing
fitness. (Both Darwin and
Wallace came to this realization after reading the
economist Thomas Malthus).
For natural selection, two additional properties are
If the fitness function is external evaluation of an individual
(e.g. an objective function, measuring some behaviour or quantity to
be optimized) then we have artificial selection.
- Creation or construction of offspring is a function of individuals
in their environment.
- Instrinsic Fitness --- No External Fitness Function
- Fitness -- determining reproductive success -- is
not given as an external function,
but emerges as a property of self-replication, and of the
interaction among individuals and between
an individual in its environments.
That is, it arises as an effect on reproduction in terms of
Evolutionary methods have been applied to optimization, design and
programming problems in the areas of Genetic Algorithms,
Genetic Programming, Evolutionary Computation, Artificial Neural Networks,
and other computationally-driven approaches.
Self-reproduction is missing from all genetic algorithm applications
of evolution, although some genetic algorithms pit individuals
against one another in direct competition. Almost all current implementations
of evolutionary algorithms on-line are instances of artificial selection,
and even most of these use an external fitness function.
- Many (computational) researchers would do not require self-reproduction as
a criterion for natural selection. Indeed, requiring it is somewhat
problematic since it can, in a trivial form, usually be incorporated in a
trivial way. Yet non-trivial self-reproduction is present in all natural evolving systems.
- I would like to thank to Dr. T.S. Ray for articulately
clarifying for me the distinction between natural
and artificial selection. Historically human beings have been applying
artificial selection for roughly 10,000 years in agriculture and
animal breeding. Artificial selection has only produced changes of
degree in qualities already present in nature. It seems natural
selection is necessary for more radical evolutionary transitions (e.g.
changes in genetic systems, advant of eucaryotes, multicellular differentiation,
segmentation, changes in body-plan, and even minor qualitative change).
Copyright (c) by C. Nehaniv, University of Aizu, 1995-96