The Basic Theory:
The theory of evolution teaches that the complex life forms on Earth that we see today (mammals, birds, insects, plants) evolved over millions of years from much simpler life forms (bacteria, single celled organisms) via a process called natural selection. Minor mutations occur in individuals over generations. If these mutations are beneficial, the animal has a slightly better chance of survival and passes the mutation on to its off spring. (For example, a slight mutation that makes the animal run slightly faster may mean that it can better escape being eaten by predators.) Over time these mutations lead to animals evolving that cannot inter breed with each other â€“ a new species has evolved.
Man can speed up the natural selection process and use this to breed superior animals for domestic use. Pigeon breeders, for example, can enhance the natural selection process by selecting the best birds they own for breeding. By careful selection and re-breeding, the pigeon fanciers are able to produce faster, better homing birds.
Fossils show examples of evolutionary animals that are the ancestors of several modern s
pecies. The fossil record and abundant other evidence testify that organisms have evolved through time. One example is the fossil skeleton of Archaeopteryx - this is an animal that lived many millions of years ago and seems to be a cross between a reptile and a bird.
"Survival of the fittest" is a simple way to describe natural selection; a more technical description speaks of differential rates of survival and reproduction. That is, rather than labelling species as more or less fit, one can describe how many offspring they are likely to leave under given circumstances.
Drop a fast-breeding pair of small-beaked finches and a slower-breeding pair of large-beaked finches onto an island full of food seeds. Within a few generations the fast breeders may control more of the food resources. Yet if large beaks more easily crush seeds, the advantage may tip to the slow breeders. In a pioneering study of finches on the Galapagos Islands, Peter R. Grant of Princeton University observed these kinds of population shifts in the wild.
Evolution can help explain how life first appeared on earth:
The origin of life remains very much a mystery, but scientists have learned how primitive building blocks of life (nucleic acids, amino acids etc) could have formed and organized themselves into simple life forms (self-replicating, self-sustaining bodies). Analysis of space dust carried out by NASA hints that quantities of these primitive building blocks might have originated in space and fallen to earth in comets. This scenario may solve the problem of how life arose when our planet was young.
Computer modelling of evolution has shown that natural selection can push evolution in one direction and produce sophisticated structures in surprisingly short times (tens of thousands of years).