What genotypic features explain the evolvability of organisms that have
to accomplish many different tasks? The genotype of behaviorally complex
organisms may be more likely to encode modular neural architectures
because neural modules dedicated to distinct tasks avoid neural
interference, i.e., the arrival of conflicting messages for changing the
value of connection weights during learning. However, if the connection
weights for the various modules are genetically inherited, this raises
the problem of genetic linkage: favorable mutations may fall on one
portion of the genotype encoding one neural module and unfavorable
mutations on another portion encoding another module. We show that this
can prevent the genotype from reaching an adaptive optimum. This effect
is different from other linkage effects described in the literature and
we argue that it represents a new class of genetic constraints. Using
simulations we show that sexual reproduction can alleviate the problem of
genetic linkage by recombining separate modules all of which incorporate
either favorable or unfavorable mutations. We speculate that this effect
may contribute to the taxonomic prevalence of sexual reproduction among
higher organisms. In addition to sexual recombination, the problem of
genetic linkage for behaviorally complex organisms may be mitigated by
entrusting evolution with the task of finding appropriate modular
architectures and learning with the task of finding the appropriate
connection weights for these architectures.
