The Creative Role of Natural Selection
The genetic changes by which species adapt to their environment are the underlying structure of evolutionary progress. However, genetic opportunities at any time are limited. The reason for this is that the cost of evolution to a population is probably high, especially if many gene changes are being selected simultaneously. It is therefore, hardly surprising to find that many species become extinct because of changing environment to which they are unable to respond effectively. These evolutionary limitations extend also to the direction toward which a species is capable of evolving. The genetic endowment of a species produced by its past evolutionary history thus closes off certain evolutionary pathways and opens other which appear to be unique and “creative”. In such sense, the creativity one may observe in evolution is restrictive; that is guided by all of its many prior historical interactions.
The creativity of evolution, however, does not mean “purposefulness” in the human sense. Except for artificial selection, there are no observable agents either within or without the organism that are consciously capable of directing evolution toward any particular stage. According to the modern view, evolutionary creativity is primarily caused by the important role played by natural selection as it acts upon genetic variability and thereby exposes a species too further selection for the same or closely connected environment.
These considerations lead to the following important distinction. If we were artificially to partition the causation of evolution into two forces, selection and mutation, the argument that mutation alone is insufficient to produce most of the observed complex biological structures would be quite true. Without the creativity of selection, millions of possible structures may be produced at random, but it is hardly likely that any of them will show the remarkably precise functional relationships of organs such as vertebrate eyes or the human brain. It is primarily because of the guiding role of selection in choosing only those mutations that increase vision functionality in animals fore say and intelligence in humans that structures such as the eyes and brain have evolved. In other words, the random process of mutation produces the variation which natural selection then molds into structures which could not have arisen all at once by themselves. Ads aptly phrased by Fischer, “Natural Selection is a mechanism for generating an exceedingly high degree of improbability”.
Restriction of future genetic change because of natural selection, however, does not mean that each type of organism must evolve a unique set of structures, different from those evolved in all other evolutionary lines. Many different organisms have similar phenotypic adaptations which have evolved separately, such as eyes bearing retinal pigments, lenses and focusing devices. In such instances, called “parallelism” or “convergence’, different genes in different organisms act to produce the same phenotypic result. Thus, on the one hand, they bear many similar features because they have faced many similar adaptive problems.
Fischer, R.A. The Genetical Theory of natural Selection.
Strickberger, M.W. 1976. Genetics.