The spread in fitness values is so large as to impend "chaotic" shifts in biogeography (and, ultimately, evolution) that are not understandable with models specific to species or functional groups; rather, a systematic study of key physiological and developmental parameters is merited.
These results suggest that in unicellular organisms, AP in key growth pathways such as the Ras/PKA pathway (Olson-Manning et al. 2012) may be resolved over time by spreading the fitness cost to downstream genes, allowing phenotypic flexibility in changing environments.
The essential difference between neutral genetic drift and adaptive evolution is that in the former case mutations that have no substantial effect on fitness spread stochastically in a population, while in the latter case mutations spread because they are beneficial and so favored by selection.
Even in a fully susceptible population, a resistant virus can only spread if its fitness exceeded 40%.
Teresa Avelar et al. then proposed that rearrangements could spread due to fitness advantages provided by the rearrangement during mitotic growth (Teresa Avelar et al., 2013; Colson et al., 2004).
Populations spread out in fitness have rather different coalescence properties than neutral populations, which are described by Kingman's coalescent (Kingman 1982).
Male-sterile mutants may initially spread because of fitness advantages, but finally the scarcity of pollen drives the population to extinction.
This could represent a case of a unique adaptive peak or a case of various peaks of equivalent fitness, spread over a rugged landscape, and potentially connected between them.
Once a resistant virus with high fitness spreads in the population, the relatively rare de novo development of resistance in other people can be completely neglected because it is out-weighted by the multiplication of the virus in the population.
The variant code can spread if the invasion fitness is higher than the fitness of the established code.
