Tag: theories of evolution

• Darwinism is an evolutionary theory proposed by Charles Robert Darwin, an English Naturalist. He believed that evolution is a gradual, rather than a sudden biological event. His theory was based on several facts, He sailed round in Beagle, his ship observations and inferences. They are 1) overproduction, 2) constancy in population, 3) struggle for existence, 4) natural selection.
  
• The prodigality of production or overproduction: Every organism tends to increase its population in large proportions. For example, Paramecium divides by binary fission at the rate of three to four times a day. At this rate, the volume of all the paramecia equals to 10,000 times that of the earth at the end of the 9000th generation in the absence of any check.
• Constancy in population: However, such an abnormal increase is not noticed in the population of any species in nature as the offspring die in large number before reaching the reproductive age. It is true that the food and the other sources do not increase in the same proportion as that of the population.
• Struggle for existence: As the food sources are limited, severe competition exists among the members of a population. Darwin called it a struggle for existence.
• Natural selection: The organisms with less reproductive success are not represented in future generations, however, fit they may be in the struggle for existence. This is called the Natural selection. Herbert Spencer called this phenomenon Survival of the fittest.
• Darwinism failed to explain the mechanism by which variations occur. Thus Darwin faced the criticism "DARWINISM EXPLAINS THE SURVIVAL OF THE FITTEST BUT NOT THE ARRIVAL OF THE FITTEST".

• Darwinism is an evolutionary theory proposed by Charles Robert Darwin, an English Naturalist. He believed that evolution is a gradual, rather than a sudden biological event. His theory was based on several facts, observations and inferences. They are 

• The prodigality of production or overproduction: Every organism tends to increase its population in large proportions. For example, Paramecium divides by binary fission at the rate of three to four times a day. At this rate, the volume of all the paramecia equals to 10,000 times that of the earth at the end of the 9000th generation in the absence of any check.
• Constancy in population: However, such an abnormal increase is not noticed in the population of any species in nature as the offspring die in large number before reaching the reproductive age. It is true that the food and the other sources do not increase in the same proportion as that of the population.
• Struggle for existence: As the food sources are limited, severe competition exists among the members of a population. Darwin called it a struggle for existence.
• Natural selection: The organisms with less reproductive success are not represented in future generations, however, fit they may be in the struggle for existence. This is called the Natural selection. Herbert Spencer called this phenomenon Survival of the fittest.
• He wrote Origin of Species including these points in 1859.

• The law of independent assortment was given by Mendel. He also gave the 'Law of Dominance' and 'Principle of Segregation'.

The Darwin theory of natural selection can be concluded as :

Darwin's theory of natural selection explains organic evolution as follows : 

• The human population increases exponentially when the resources are unlimited according to Darwin.
• Unlimited resources are the ones that increases arithmetically.

In 1859, Charles Darwin in his book 'Origin of species' stated the 'theory of evolution'. in this theory he has stated that no two individuals are the same but they have variations which help them in survival. This is called a natural selection. According to his theory, evolution is a slow and continuous process as it creates variation among individuals, these variations may or may not be passed among the offsprings. He had not explained the population growth and the phylogeny of an individual.