328 Species
mean that quasispecies are not real species because they are ephemeral? Of course
not, as all species are, over a suitably extended timescale, ephemeral. That is in the
nature of evolution. What the fitness peak conception means is that a quasispecies
will remain homogeneous so long as there is a more or less unitary fitness peak. If
the peaks shift, there will be “speciation” or, stopping the pretense that quasispecies
aren’t real species, there will be real speciation.
When we attempt to apply to organisms that are not obligately sexual (that is,
which don’t have to have sex to reproduce) concepts that were specified to use with
those that are sexual, we have problems. The Recombination Model is one such
attempt. It is true that some microbial species exchange genes. Others do it more
frequently and more completely. However, there appears to be a continuum of gene
exchange all the way from almost never to almost every generation. So why should
we expect that gene transfer will provide us with the sort of cohesion of lineages and
quasispecies that it does in obligate sexual species?
FIGURE 13.6 Tracking fitness peaks. Clustering could be explained in terms of tracking
fitness peaks—deviations from the local adaptive peak would be eliminated by selection.