- Evolution is a process by which living things change over time and adapt to the conditions of their environment.
- It may be also defined as the gradual development of the characteristics of plants and animals over time.
- Everything in this world changes continuously through space and time. Changes relate to plants and animals (living organisms) are studied under ‘organic evolution’.
- The life was originated from the chemical evolution on the primitive earth which was later replaced by organic evolution.
- It is caused by changes in the gene pool of the population, usually as a result of natural selection.
- Evolution may be classified into following types. They are:
1.Adaptive radiation (Divergent evolution)
- The evolution of a number of different groups of organisms from a common ancestral group is called adaptive radiation.
- A good example of this process is the evolution of the Australian marsupials into species adapted as carnivores, herbivores, burrowers, fliers, etc.
2.Convergent evolution (Convergence)
- The process by which unrelated species evolve to resemble each other is called convergent evolution.
- In this evolution, organisms with very different ancestors become more alike because they live in the similar habitats.
- e.g., the wings of birds and bats and streamlined bodies of whales and fish are the analogous organs.
- Analogous organs are similar in function and appearance but not in origin.
3.Parallel evolution (parallelism)
- The development of organisms along similar evolutionary paths due to strong selection pressures acting on all of them in the same way is parallel evolution.
- e.g., New world and Old world porcupines shows structural resemblances.
- The evolution in which simple forms of organisms develop towards the complex structural and physiological organizations is progressive evolution.
- e.g., evolution of multicellular organisms from unicellular organisms.
- The evolution in which complex forms of organisms develop towards simpler structural and physiological organizations is called retrogressive organization.
- e.g, monocot plants are considered as more advance groups of plants with simple structure and herbaceous habitat.
Patterns of evolution (types of evolution)