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.
- 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 :
- 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.
- 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.