Darwin formulated his ideas of theory of evolution by natural selection by 1844. There are following points of his theory of evolution by natural selection on the basis of evolution.
The change in the heritable traits of a population over successive generations, as determined by shifts in the allele frequencies of genes is called evolution. All contemporary organisms are related to other through common descent. It is products of cumulative evolutionary changes over billions of years. Evolution is the source of the vast diversity of extant and extinct life on Earth. Different theories of evolution were put forward. The theory of natural selection is most acceptable theory.
Theory of Evolution by Natural Selection
Darwin’s Theory of Evolution by Natural Selection and its key points are as follow:
Overproduction of Population
- All organisms have great reproductive potential. They have high capacity of reproduction For example:
- A female oyster releases about 100,000 eggs with each spawning.
- A female sea star releases about I million eggs each season.
- Thus, A half million female sea stars can produce another million eggs. If this repeated over just a few generations, it will soon fill up the oceans.
- A female robin (bird) lays four fertile eggs each season. If each produces four more robins. It will cause unimaginable resource problems in just a few years.
Inherited variations arise by random mutation. Two individuals are never exactly alike. Some of these genetic variations give advantage to the individuals. But some variations are harmful to an individual. Some other variations are neither helpful nor harmful. variations are called neutral. These variations can be passed on to offspring.
Struggle for Survival
The resources are limited. Therefore, a constant struggle started. Many more offspring are produced than resources can support Therefore, many individuals die. Darwin reasoned that these individuals have less adaptive traits. Some individual remains alive. These individuals have adaptive traits.
Adaptive traits are transferred in subsequent generations. The organisms with maladaptive traits have less chance to reproduce. Thus, the maladaptive traits become less frequent in a population. Finally, they are eliminated.
Darwin formulated a theory with these ideas. This theory explains following points:
- How the tortoises and finches of the Galapagos Islands changed over time.
- It also explains how some animals like ancient South American horses can become extinct. Sometimes, a group of animals face a new environment. It cannot adapt in the climatic changes, food shortages, and other environmental stressors. Therefore, they become extinct.