QUANTITATIVE GENETICS AND EVOLUTION - IS OUR UNDERSTANDING OF GENETICS SUFFICIENT TO EXPLAIN EVOLUTION

We have provided a bridge between geneticists, who tend to concentrate on genes and their frequencies, and other biologists, who are much more aware of how severely the environment constrains and limits life. This bridge is the recognition that a. fitness is a product of important component traits, b. these and most other traits consume environmental resources and these resources are additively related and can sum to no more than the total resources an animal can obtain from the environment, c. allele frequencies can alter only to the degree that the phenotypes that carry the alleles reproduce themselves successfully, i. e. are fit, d. fitness must rise, because it is never free from natural selection upwards, to the point where it can rise no further, because all environmental resources available to an animal are being used most efficiently, e. in this state of adaptation, fitness is completely limited by the environment and all other traits important to the animal are constrained to a greater or lesser degree at intermediate, ''optimal'' values, and f. traits or molecules unimportant to animals, so that they are completely neutral with respect to fitness, are free to drift genetically and hence gene substitutions can occur at rates related to their mutation rates. This bridge between genetics and other parts of biology shows that the various theories apparently causing concern for the modern synthetic theory of evolution are entirely compatible with it. Bursts of rapid evolutionary change between long periods of evolutionary stasis are the necessary consequences of strong natural selection acting on fitness, in ecosystems that are stable until external forces cause them to change. Neutral (random) evolution describes the fate of genetic material that is unimportant for organisms, i. e. material that is truly neutral with respect to fitness.