Game Development Reference
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mutation. In short, it endeavors to replicate the genetic process involved
in biological evolution computationally.
Genetics, or the study of heredity, concentrates on the transmission
of traits from parents to offspring. It not only examines how physical
characteristics such as hair and eye color are passed to the next
generation, but it also observes the transmission of behavioral traits
such as temperament and intelligence. All cells in all living beings,
with the exception of some viruses, store these traits in chromosomes .
Chromosomes are strands of deoxyribonucleic acid (DNA) molecules
present in the nuclei of the cells. A chromosome is divided up into a
number of subparts called genes . Genes are encoded with specific traits
such as hair color, height, and intellect. Each specific gene (such as that for
blood type) is located in the same location on associated chromosomes
in other beings of the same species. Small variations in a gene are called
alleles . An allele will flavor a gene to create a slight variation of a specific
characteristic. A gene that specifies the blood group A in different people
may present as an allele for A+ and in another person an allele for A - .
Chromosomes come in pairs, and each cell in the human body contains
23 of these pairs (46 chromosomes total) with the exception of sperm
and ova, which only contain half as much. The first 22 pairs of human
chromosomes are the same for both males and females, and the 23rd pair
determines a person's sex. At conception, when a sperm and ova meet,
each containing half of its parent's chromosomes, a new organism is
created. The meeting chromosomes merge to create new pairs. There are
8,388,608 possible recombinations of the 23 pairs of chromosomes with
70,368,744,000,000 gene combinations.
Evolutionary computing simulates the combining of chromosomes
through reproduction to produce offspring. Each gene in a digital
chromosome represents a binary value or basic functional process.
A population is created with anywhere between 100 and many thousands
of individual organisms where each individual is represented usually by a
single chromosome. The number of genes in the organism will depend on its
application. The population is put through its paces in a testing environment
in which the organism must perform. At the end of the test each organism is
evaluated on how well it performed. The level of performance is measured by
a fitness test. This test might be based on how fast the organism completed
a certain task, how many weapons it has accumulated, or how many human
players it has defeated in a game. The test can be whatever the programmer
deems is a best judgment of a fit organism. Once the test is complete, the
failures get killed off and the best organisms remain.
These organisms are then bred to create new organisms, which make up
a new second-generation population. Once breeding is complete, first-
generation organisms are discarded and the new generation is put through
its paces before being tested and bred. The process continues until an optimal
population has been bred.
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