Natural Selection and Adaptation
It is a commonplace observation that every living being is so constructed that it is able to live in a certain environment (Figure 6.1). A fish is adapted to live in water, a bird is an efficient flying machine, a cow and a deer have digestive organs which enable them to feed on herbage and foliage, the human mind permits man to acquire and transmit culture. The origin of this apparent purposefulness of biological organization is a riddle which several generations of biologists have attempted to solve. Some have taken the easy way out by supposing that every living species is endowed by the Creator with those features which it needs in order to live in the habitats in which it is actually found. This is, however, a spurious solution; it implicitly blames the Creator also for all the imperfections and all the sufferings found in human and biological nature.
So far the only scientifically tenable solution of the riddle was proposed by Darwin in 1859. According to Darwin, organisms become adapted to the environment in the process of evolution; this process is controlled by natural selection of genetic variants which are relatively better fitted than others to survive and to reproduce in certain environments. The theory accepted by a majority of modern evolutionists is clearly derived from Darwin's theory; however, it is just as clearly not identical with the Darwinian prototype. The changes in the theory are due to the mass of new evidence discovered by biologists since 1859. The modern theories are often referred to as neo-Darwinism, which would be a good name if it were not for the fact that it was applied also to the theories developed by Weismann and others around 1900, and they are as different from the modern ones as they were from Darwin's. Synthetic theory and biological theory of evolution