Information Technology Reference
In-Depth Information
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Fig. 15.14. Independence of the speciation transition by the mutation rate. The transition is
characterized by the average square phenotypic distance
h
g(u)
2
i
of phenotypic distribution p(u),
as a function of the control parameter G m. Each point is a single run. Same parameters as in
Fig. 15.12, varying J with = 10
3
(left) and = 5 10
2
(right).
one can see that the transition point is substantially independent of , as predicted
by the analysis of speciation in the phenotypic space, Eq. (15.28).
15.5.3. Sex
By inserting sexual reproduction (recombination) and possibly horizontal transfer
of genetic material (conjugation in bacteria, viruses and { in plants, also tumor-
inducing bacteria) we should rather consider a dierent phylogenetic path for each
gene. The history of a given gene (more appropriately, a locus) is in general dif-
ferent from that of another one, still present in the same genome. The survival
probability of a gene depends on how good the gene performs in conjunction with
the other genes. Even if only \egoistic" genes (those that maximize their survival
and reproductive probability) passes from a generation to the other, they are nev-
ertheless forced to collaborate. Moreover, genes are identical, in the sense that two
individuals or cells may carry the same gene. The survival of a gene may thus
prot of the death of another individual with the same gene, if this death increases
suciently the survival and reproductive eciency of the former. This is the ori-
gin of multicellular beings (in which reproduction is reserved to the germ line), of
insect colonies, familiar structure and many other evolutionary patterns. More in
this subject in Section 15.5.4.
Actually, forced cooperation is true only for those genes that may pass to the
following generation through the reproduction of the individual. Genes may not
follow the fate of the individual by escaping as viruses, or being horizontally trans-
ferred (plasmids). Especially in case of viruses, the direct advantage of viruses may
correspond to a great damage for the host. If for some mutation the virus content
is \trapped" inside the host and forced to follow the usual germ line to propagate,
that automatically it is forced to collaborate.
