Biologists study a great many evolutionary processes on the models of an adaptive landscape.The American biologist Sewall Wright introduced the model of the adaptive landscape into evolutionary biology at the beginning of the nineteen thirties. In actual fact, this consists of two quite different models, between which not even their author always sufficiently differentiated. This is an abstract model of either the environment and the individual organisms or the environment and populations. In the former case, the evolution of organisms in the environment can be conceived, e.g., as a three-dimensional topographical map, in which the x and y coordinates correspond to two qualities of a hypothetical organism (e.g. body weight and maximum speed of movement); in the second case, the frequency of the alleles are on the x and y axes at two different loci and the average biological fitness of the given population is on the z axis. Let us now return to the first model of an adaptive landscape. The shape of the surface of an adaptive landscape, the system of hills and valleys, is given independently of the properties of the organisms and determines the distribution of future niches in the particular environment. The projection of the points onto the surface of the adaptive landscape, i.e. coordinate z, determines the fitness of each individual organism (characterized in our model by properties X and Y). It is apparent that various combinations of X and Y are variously advantageous from the standpoint of natural selection. Mutations, i.e. a change in coordinate x or y, move the organism from one place to another, also shifting their projections onto the surface of the adaptive landscape. Only mutations that shift the projection of the organism uphill in the plane of the adaptive landscape, to places with larger coordinate z, can be fixed by natural selection. It is apparent that, under suitable circumstances, in time, organisms climb up to the peaks of the individual hills.
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