Organic Evolution Theory

Organic Evolution Theory

Organic Evolution

More and more creation of organisms by gradual change from low-category organisms to higher organisms is called organic evolution. There is much evidence regarding organic evolution.

Evidence of Organic Evolution

1. Homologous Organ

• Organs which are seen differently due to use in their function but whose internal structure and embryonic development are similar.

Example: flipper of a whale, feather of a bat, forelimb of a horse, paw of a cat and hands of a human.

2. Analogous Organ

• Organs which look similar are due to be used in similar functions, but their internal structure and embryonic development are different.

Example: Wings of butterflies, bats and birds all look similar, but their internal structure and origin are different.

3. Vestigial Organ

• These are organs which appear functionless in an organism but were functional in their ancestor.

Example: The vermiform appendix of the large intestine and the nictitating membrane of a human. The vermiform appendix is functional in herbivorous mammals even now.

4. Fossils

• Fossils are the remains of ancient plants or animals which provide evidence for evolution.

Example: Archaeopteryx.

5. Archaeopteryx

• It is a fossil that looks like a bird but bears a number of features found in reptiles.

• So, it is a connecting link between aves and reptiles.

Theories of Evolution

1. Carolus Linnaeus (1707–1778)

• His contribution to classification provides an evolutionary relationship among the organisms.

• He 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 the binomial system of nomenclature.

2. Jean-Baptiste Lamarck (1744–1829)

• Jean-Baptiste Lamarck tried to explain the evolutionary process in his book Philosophic zoologique. The theory proposed by Lamarck is known as the theory of inheritance of acquired characteristics.

• According to this theory, use and disuse of an organ lead to acquiring changes in features of that organ. These changes are also inherited by offspring.

• The favourable changes after a long period of time result in the evolution of new species. But Lamarckism was very strongly criticised by August Weismann.

3. Charles Robert Darwin (1809–1882)

• He explains the evolutionary principle in his book ‘The Origin of Species’. The theory proposed by him is popularly known as ‘the theory of natural selection’ or Darwinism.

• Darwin explained that despite having the enormous potential of fertility, the population of organisms remains within a limit. It is due to the struggle between members of the same species and different species for food, space and mates. Struggle eliminates the unfit individual.

• The fit organism possesses some variations which are favourable, and they can leave the progeny to continue the favourable variation.

• The variation when accumulated for a long time gives rise to the origin of new species. With progress in genetics, the source of variation was explained, and Darwin’s theory was modified.

Now the most accepted theory of evolution is the modern synthetic theory, in which the origin of species is based on the interaction of genetic variation and natural selection.

Additional Information

• Among the Permian, Triassic, Cretaceous and Jurassic geological eras, the Cretaceous is the newest one.

• The book which contains information about all plants is called the Red Data Book.

• Recapitulation theory was proposed by Ernst Haeckel.

• The correct taxonomic hierarchy is Kingdom → Phylum → Class → Order → Family → Genus → Species.

• At present, phylogenetic classification systems based on evolutionary relationships between various organisms are acceptable.

• Numerical taxonomy of plants is based on all observable characteristics and is easily carried out using computers.

Final Thoughts

Organic evolution refers to the gradual development of complex organisms from simpler forms over time. It is supported by various pieces of evidence, such as homologous organs (similar structure but different functions), analogous organs (similar functions but different origins), vestigial organs (functionless but present in ancestors), and fossils like Archaeopteryx, which link reptiles and birds.

Important contributors include Linnaeus, who developed binomial nomenclature; Lamarck, who proposed the inheritance of acquired characters; and Darwin, who introduced the theory of natural selection.

Today, the modern synthetic theory combines genetics with natural selection to explain evolution, showing how life diversifies and adapts over generations through continuous change.