Organic Evolution

Organic Evolution

More and more creation of organism by gradual change from low categories organism to higher organism is called organic evolution. There are several evidence regarding organic evolution.

• Homologous organ: Organ which are seen different due to use in its function but internal structure and embryonic development are similar. Ex – Flipper of whale, feather of bat, forelimb of horse, Paw of cat and hands of human.
• Analogous organ: Organ which looks similar due to be used in similar function but their internal structure and embryonic development ar different. Ex –Wings of butterfly, bats and birds all looks similar but their internal structure and origin are different.
• Vestigial organ: These are organs which appear functionless in an organism but was functional in their ancestor. For example vermiform appendix of large intestine and nictitating membrane of human. Vermiform appendix is functional in herbivorous mammal even now.
• Fossils – Fossils are the remains of ancient plant or animal which provide evidences for evolution. Example – Archaeopteryx.
• Archaeopteryx: It is a fossils looks like bird but bear a number of features found in reptiles. So, it is a connecting link between aves and reptile.

Theories of evolution

1. Carolus Linnaeus (1707 – 1778)

His contribution to classification provide in evolutionary relationship among the organism. He was also supported an idea that no species is new. Each and every species originates from some pre-existing species.

• He wrote ‘species plantarum’ and proposed binomial system of nomenclature.

2. Jean Baptist Lamarck (1744 – 1829)

Jean Baptist Lamarck tried to explain the evolutionary process in his book Philosophic zoologique. The theory proposed by Lamark is known as theory of inheritance of acquired characters. According to this theory use and disuse of an organ lead to acquiring change in features of that organ. These changes are also inherited to off spring. The favourable changes after long period of time result in evolution of new species. But Lamarckism was very strongly criticized by August Weismann.

3. Charles Robert Darwin (1809 – 1882)

He explain the evolutionary principle in his book ‘The origin of species’. The theory proposed by him is popularly known as ‘Theory of natural selection’ or Darwinism. Darwin explained that despite having the enormous potential of fertility, the population of organism remains within a limit. It is due to struggle between members of same species and different species for food, space and mate. Struggle eliminates the unfit individual. The fit organism possess some variations which are favorable and they can leave the progeny to continue the favourable variation. The variation when accumulated for long time give rise to origin of new species with progress in genetics, the source of variation were explained and Darwin’s theory was modified. Now the most accepted theory of evolution is Modern synthetic theory, in which origin of species is based on the interaction of genetic variation and natural selection.

• Among Permian, Triassic, Cretaceous and Jurassic geological era cretaceous is the newest one.
• The book which contains information about all plant is called red data book.
• Recapitulation theory was proposed by Erunst Haeckel.
• The correct taxonomic hierarchy is – Kingdom → Phylum → Class → Order → Family → Genes → Species.
• At present phylogenetic classification system based on evolutionary relationships between various organisms are acceptable.
• Numerical taxonomy of plant is based on all observable characteristics easily carried out using computers.