DARWIN’S THEORY OF EVOLUTION:

• Charles Darwin wrote his famous book “Origin of Species.
• He threw new insights on the evolution of species.

Some salient points of Darwin’s theory are as follows:

• Organisms have unlimited capacity to reproduce
• Organisms can reproduce offspring at a fast pace.
• This is necessary for survival, because a higher number of offspring ensures that at least some of them could survive.
• Each organism has to struggle for its day to day survival.
• For example; a frog lays thousands of eggs at one go.
• The spawn is released in water and it is left to fend for itself.
• Most of the eggs are either washed away or are eaten by predators.
• However, Some portions of eggs from the spawn develop into tadpoles.
• Once again, many tadpoles are eaten by predators; leaving a few. which develop into adults.

Natural Selection:

• Different individuals of a particular species have different traits.
• Those with more suitable traits are selected by nature.
• Each organism needs a particular trait for finding food and finding a mate.
• Those with better traits are finally able to pass on their traits to the next generation.

Survival of the Fittest:

• Those organisms which are the fittest are able to survive, while others perish.
• That is how many species become extinct and some Species continue to evolve over a period of time.

EVOLUTION AND CLASSIFICATION

• The modern system of classification is based on evolutionary relationships.
• Due to this, this is also known as phylogenetic classification.
• The kingdom is the highest taxa, while the species is the lowest taxa.
• Members of a species have a higher number of common characters, than members of a kingdom.
• For example; all human beings belong to the species Homo sapiens.
• Human beings can interbreed; irrespective of their race or skin colour.
• All human beings come under the class mammalia; as do the monkeys, elephants and cows.
• Apparently, each species of the class mammalian is quite different yet they have certain common characters; like hairs on the body and mammary glands in females.
• Similarly, all animals are eukaryotes and the cell wall is absent in their cells.
• The degree of similarity or dissimilarity shows that all animals have evolved from a common ancestor.

Some of the important sources which provide evidences for evolution are :

HOMOLOGOUS ORGANS

• Organs which have common design but serve different functions in different animals are called homologous organs.
• For example; the forelimbs of all tetrapods are composed of humerus, radio-ulna, tarsals and metatarsals.
• Yet, the forelimbs of frogs are adapted to a jumping movement, those of birds are used for flying and those of humans are used for handling tools.
• This shows that frogs, birds and humans have evolved from a common ancestor.

ANALOGOUS ORGANS

• Organs which have different designs but serve a common function in different animals are called analogous organs.
• Wings of birds and wings of bats are good examples of a pair of analogous organs.
• Wings of birds are composed of all the bones of the forelimb and are covered with feathers.
• Wings of bats are mainly composed of the digital bones and a thin membrane covering the structure.
• Yet wings in both the organisms are used for flying.