Evolutionary landscape

An evolutionary landscape is a metaphor, a construct used to think about and visualize the processes of evolution (e.g. natural selection and genetic drift) acting on a biological entity (e.g., a gene, protein, population, species). This entity can be viewed as searching or moving through a search space. For example, the search space of a gene would be all possible nucleotide sequences. The search space is only part of an evolutionary landscape. The final component is the "y-axis," which is usually fitness. Each value along the search space can result in a high or low fitness for the entity. If small movements through search space cause changes in fitness that are relatively small, then the landscape is considered smooth. Smooth landscapes happen when most fixed mutations have little to no effect on fitness, which is what one would expect with the neutral theory of molecular evolution. In contrast, if small movements result in large changes in fitness, then the landscape is said to be rugged. In either case, movement tends to be toward areas of higher fitness, though usually not the global optima.

What exactly constitutes an "evolutionary landscape" is confused in the literature. The term 'evolutionary landscape' is often used interchangeably with 'adaptive landscape' and 'fitness landscape', although some authors distinguish between these terms. As discussed below, different authors have different definitions of adaptive and fitness landscapes. Additionally, there is a large disagreement whether evolutionary landscape should be used as a visual metaphor disconnected from the underlying math, a tool for evaluating models of evolution, or a model in and of itself used to generate hypotheses and predictions. Clearly, the field of biology, specifically evolutionary biology and population genetics, needs to come to a consensus about what an evolutionary landscape is and how it should be used.

According to McCoy (1979), the first evolutionary landscape was presented by Armand Janet of Toulon, France in 1895. In Janet's evolutionary landscape, a species is represented as a point or an area on a polydimensional surface of phenotypes, which is reduced to two dimensions for simplicity. The size of the population is proportional to the amount of variation within the population. Natural selection (the influence of the exterior features) is represented by a vector. Unlike the evolutionary landscapes of those who would follow, in Janet's concept, natural selection pulls species toward the minima instead of the maxima. This is because the y-axis doesn't represent fitness but stability. One important aspect of Janet's evolutionary landscape (versus Wright's) is that the landscape changes as the environment changes.

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