Natural Selection is a simple yet very powerful idea, the concept that the blind forces of nature can act in place of a purposeful breeder to bring about change in a species leads to some profound conclusions. At the same time it is also one of the most misunderstood and reviled theories in science today.
What is Natural Selection?
Natural Selection is an explanation of the variety of life that we see all around us that is modeled from artificial selection performed by human breeders of animals and crops. One of the most easily grasped examples of this is dog breeders. Over the last several thousand years that canines have been domesticated we have molded them from a few varieties of wolf into the almost dizzying number of breeds we have today. The ancestors of each breed were selected for particular traits that were useful or otherwise desirable to the breeders of the time. The end result was an animal that in some cases bears only a passing resemblance to the original stock.
Where Natural Selection differs is that it posits that the role of intelligent breeder can be replaced by unintelligent natural forces. In this case the qualities selected for are not matched against some future ideal but what is best suited for the existing environment. In other words the forces influencing evolution can not select for the eventual creation of a particular body plan or anatomical structure, there is no room for foresight in this system, each change must be adaptive in the environment that the organism finds itself.
It is now accepted that whales and dolphins evolved from land dwelling animals, natural selection did not decide to turn them into sea faring creatures and induce the changes necessary, each intermediate step had to suit the animal’s life style at the time and make it better able to compete with it’s rivals.
The unintelligent natural forces I mentioned above can be climate, terrain or other organisms. In the later case one situation that can result is a sort of “arms race” where a change in one organism influences a change in another which in turn feeds back to the first. Consider a predator/prey relationship. If the prey organism by chance starts down a course of running speed as the means of avoiding becoming dinner then the slower predators will tend to eat less often than their faster compatriots. They will then tend to die more frequently and have fewer offspring. In this way the genes for faster running speed will spread through the population and become dominant in the predators. In turn as the predators get faster the slower prey will succumb to them more often and leave the responsibility of continuing the species to the sprinters among the prey population. And so on. This will presumably continue until some sort of fundamental limit is reached.
There is also an intuitive notion that evolution is a sort of ladder whereby bacteria and other simple organisms are on the bottom and are “primative” with fish coming after them, mammals after fish and Humans at the top reresenting the pinnacle of evolution. Tempting as it is however this is absolute nonsense, there is no steady march toward some idealised perfection in the progression from “simpler” organisms to “advanced” organisms. Each animal or plant or single celled organism is as evolved as any other, each as suited to it’s environment as it needs to be to survive.