Question

Define evolution. Give the principles of Darwin’s theory of natural selection. Mention any one objection to it.

Answer 1

The long process of change by which individuals originated from apelike ancestors is human evolution. Scientific evidence suggests that all people's shared physical and behavioural characteristics derived from apelike ancestors and evolved over a period of about six million years.

Complete Answer:
- Evolution is the change in the features of a species over many generations and depends on the natural selection process. Evolution relies on genetic variation in a population that affects the physical characteristics (phenotype) of an organism. Charles Darwin's theory of evolution states that evolution occurs through natural selection.
- Individuals in a species exhibit differences in physical characteristics. This variation is due to variations in their chromosomes.
- First proposed in Darwin 's book "On the Origin of Life" in 1859, the theory of evolution by natural selection is the mechanism by which organisms evolve over time because of changes in inherited physical or behavioural traits. Changes that cause an organism to environmental conditions more can assist it to survive and have more offspring.

Darwin 's natural selection mechanism consists of four elements:
(I) Variation: Organisms (within populations) display individual differences in appearance and behaviour. These variations can include body size, hair colour, facial markings, speech characteristics, or the number of offspring. On the other hand, certain characteristics display little to no difference between individuals — for example , the number of eyes in vertebrates.
(II) Inheritance: Some traits are consistently passed from parent to offspring. Such traits are hereditary, while other traits are strongly influenced by environmental conditions and are weakly heritable.
(III) Strong population growth rate: Most populations have more offspring each year than local resources can support a struggle for resources. Every generation is experiencing significant mortality.
(IV) Differential survival and reproduction of the species. Individuals with characteristics that are well suited to the struggle for local resources will contribute more offspring to the next generation.

The objection to Darwinism is as follows:
- Darwin has not been able to explain the origin and cause of the variations that occur during evolution.
- He emphasised the importance of the most appropriate organisms. Later, it was proposed that fit and fitter types may also coexist.
- During Darwin, the concept of inheritance was not present.Darwin thus believed in the 'pangenesis' hypothesis. This theory explains that organs give rise to a certain framework for growth that passes to gonads.

Note: The phenotype of an individual organism is the result of both its genotype and its environmental influence. A significant part of the population's phenotypic variation is caused by genotypic variation. The modern evolutionary synthesis defines evolution as a change in this genetic variation over time.