Abstract:

Background & Aims: Natural selection assumes that there is an expected fitness advantage (or aim) for any selection of gene mutations or phenotypic characteristics. However, the fitness of the selected gene mutation/phenotypic characteristic might vary as it spreads throughout a population or might vary with changing living environments over both evolutionary and ecological scales. This may result in a “paradox of stationary fitness landscape” in which an expected fitness advantage of a selected gene mutation/phenotypic characteristic might therefore not exist. Based on a dynamic state but not a stationary fitness landscape, we propose that natural selection might exhibit path-dependent selection.

Summary: In path-dependent selection, the gene mutation or phenotypic characteristics are produced completely at random, but some might meet a specific condition which could generate positive feedback as they spread. Such positive feedback might also be that such matched conditions could further facilitate the occurrence of a genetic trait/phenotypic characteristic. The positive feedback effect will therefore increase the probability of a genetic trait or phenotypic characteristic in specific conditions, meaning natural selection will depend on the probability of path, but not fitness value. Analogy to that many paths lead to a bus stop near your office building, the path-dependent selection argues that the quickest path might be mostly selected, especially when the bus stop is at a fixed location and selection pressure is strong. However, the other paths may also be selected especially when the bus stop could change location or selection pressure is weak. In path-dependent selection, both evolutionary history and distribution of ecological characteristics will greatly affect the evolution of any path. Using this understanding, different pathways can be understood as different points of speciation, where the distribution of species is similar to the peaks of a mountain in which the paths with a high probability will shape peaks, while many other species with low path probability will not separate into other peaks, creating sister species, cryptic species, or redundant species.

Prospects: Path-dependent selection can be described by the complex function, a mathematical skill widely used in modern physics. Through complex function, we can describe how multiple factors shape a probability of path-dependent selection in speciation peaks and the oscillation of species peaks. Different pathways, which could also be understood as different dimensional viewpoints, will demonstrate a different understanding of the evolutionary aim of a gene mutation, phenotypic characteristic.

Key words: natural selection, fitness, path-dependent selection, speciation, species diversity