Evolution and classification

Evolution and classification are linked to each other. There is different evidence of evolution given-

  • Homologous organs are the organs evolved from the same ancestors but they have different functions. For example, the forelimb of a horse and the wings of a bat. The Flippers of the whale, the human hand are other examples of homologous organs.

Examples of homologous organs

  • Analogous organs are the organs that arise from different ancestors but have the same function. For example, wings of bats, wings of birds, wings of insects etc.

Examples of analogous organs 

  • Paleontological (fossil) evidence was also given for evolution. The dead remains of the organisms are known as fossils. For example, Archaeopteryx possesses features of both reptiles and birds. This concludes that birds evolved from reptiles. There are two methods for finding the age of the fossils- one is carbon dating and the other is by digging. In the digging method, the deeper the fossil is, the older it is. Biogenetic law states that stages of development of an animal embryo are the same as adult animal stages. 
  • Vestigial organs are rudimentary in nature. They have lost their function through evolution. For example, appendix in humans, muscles of ears, wisdom tooth etc.

Evolution by Stages
Evolution can take place in stages also. For example, the evolution of eyes. Flatworms have rudimentary eyes, whereas insects possess compound eyes. In the last humans have binocular vision.
The evolution of feathers is also an example of evolution by stages. For example, dinosaurs have feathers but are unable to fly. But later on, birds used feathers for flying.

Molecular Phylogeny
It is also evidence for evolution. According to this, changes in DNA during reproduction are the basic events of evolution. Organisms that are related to each other most distantly will have greater differences in their DNA.

Evolution by Artificial Selection
Artificial selection selects special phenotypic characters to produce organisms with enhanced characteristics. For example, plants that are disease or insect resistant. Artificial selection can be used to produce different cabbage varieties such as broccoli, cauliflower, red cabbage etc.

Human Evolution
Excavating fossils, time dating and determination of DNA sequences are used to study human evolutionary relationships. The study of human evolution indicates that all of us belong to a single species that evolved in Africa and then spread across the world in stages.

The stages of human development are as follows-