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The fact that RIS and IS transposition exhibit a behavior similar to muta-
tion further reinforces the uniqueness of recombination. We will see in the
next section that populations undergoing recombination alone behave very
strangely: they evolve very smoothly without appreciable oscillations on
average fitness and are constantly trying to close the gap between average
and best fitness.
Recombination
The evolutionary dynamics of recombination show that all recombinational
operators, from the most conservative (gene recombination) to the most dis-
ruptive (two-point recombination), display a homogenizing effect (Figure
12.4). For obvious reasons, these recombination-specific dynamics are called
homogenizing
dynamics. Note that, in all cases, the plot for average fitness
closely accompanies the plot for best fitness and, given enough time, the
plots tend to overlap and populations lose all genetic diversity (see, for in-
stance, plots
c
,
g
, and
h
). Note that this happens despite the recombination
rate or the kind of recombinational operator involved and, in fact, by looking
solely at these plots, not only is impossible to distinguish one kind of recom-
bination from another but also more efficient systems from less efficient
ones. Indeed, populations subjected to recombination alone become invari-
ably less and less diverse with time, becoming totally incapable of adapta-
tion. Obviously, if populations converge to this stage before finding a good
solution, they become irrevocably stuck in that point if no other, non-ho-
mogenizing operators are available. As the small success rates obtained for
recombination emphasize (see Figure 12.1), when populations evolve exclu-
sively by recombination, most of the times they converge before finding a
good solution. This shows that recombination should never be used as the
only source of genetic variation if an efficient adaptation is what is desired.
Note also that the oscillations on average fitness are less pronounced in
homogenizing dynamics. Nevertheless, oscillations increase slightly with
recombination rate showing that highly recombining populations are more
resilient and will take more time before they become stagnant.
In summary, recombination is a homogenizing operator and, therefore,
inappropriate to create genetic diversity; in the long run, populations exclu-
sively subjected to recombination become stagnant. Consequently, recombi-
nation is removed from the center of the evolutionary storm and new roles
must be proposed for this operator. For one thing, it can play an important
role in the duplication of genes if it is combined with other genetic operators
