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up by the selection operator. And the copied chromosomes are none other
than the chromosomes of the individuals of the next generation. But repro-
duction is not yet completed. Before that, the replicated chromosomes will
undergo genetic modification. This modification is done by the genetic op-
erators of mutation, inversion, transposition, and recombination (called modi-
fication operators in order to distinguish them from the genetic operators of
replication and selection). But for now let's concentrate on selection and
replication.
Figure 3.10 gives an example of how the selected individuals are repli-
cated (the modification operators and elitism were switched off so that repli-
cation and selection could be better understood). For instance, chromosome
0, one of the best of generation 0, left two daughters (chromosomes 1 and 3
of generation 1); chromosome 1, also one of the best of this generation, left
only one descendant (chromosome 9 of generation 1); chromosome 7, also
one of the best, left two daughters (chromosomes 2 and 4 of generation 1);
but chromosome 8, also one of the best, died without leaving offspring; the
second best (chromosome 3) was more lucky and left two daughters (chro-
mosomes 7 and 8 of generation 1); and although the most unfit of generation
0 (chromosomes 2, 4, and 5) did not reproduce, chromosome 6, a mediocre
individual, left the biggest progeny (chromosomes 0, 5, and 6 of generation
1). The outcome of such an “evolutionary” process with just replication and
Generation N: 0 Generation N: 1
01234560123456 01234560123456
OOOaaabAAAcabb-[0] = 6 OONbcaaAaAaacc-[0] = 4
AAcbbabNONaaac-[1] = 6 OOOaaabAAAcabb-[1] = 6
ANaccbcNAAcbbc-[2] = 2 AcOaccbAbNbabc-[2] = 6
OAOccbaAOAbcab-[3] = 5 OOOaaabAAAcabb-[3] = 6
AAAbbabNcObcca-[4] = 3 AcOaccbAbNbabc-[4] = 6
NbacabbNbccbbc-[5] = 2 OONbcaaAaAaacc-[5] = 4
OONbcaaAaAaacc-[6] = 4 OONbcaaAaAaacc-[6] = 4
AcOaccbAbNbabc-[7] = 6 OAOccbaAOAbcab-[7] = 5
AaOacccAbbbaca-[8] = 6 OAOccbaAOAbcab-[8] = 5
AOAcaaaNaNbaab-[9] = 4 AAcbbabNONaaac-[9] = 6
Figure 3.10.
Illustration of replication and selection. Only replication and roulette-
wheel selection are switched on so that these operators could be better under-
stood. Note, for instance, that chromosome 8 of generation 0 (one of the best of
this generation) did not leave descendants, whereas chromosome 6 (a mediocre
individual) left the biggest progeny (chromosomes 0, 5, and 6 of generation 1).
