Theories of Evolution (Part-II)

Darwin’s Theory of Evolution: The theory of natural selection was proposed by Charles Darwin and Alfred Russel Wallace in their common publication. Both of them conducted scientific data collection from individual population survey. Charles Darwin travelled for 5yrs expedition around the world on the ship H.M.S Beagle. During this journey, he made observation of several animals and plants. He keenly observed the similarities among organisms and draw evolutionary relationship. In addition, economist Thomas Malthus’s report on workers recognized that competition between species leads to the struggle for existence. Considering Wallace’s view and Malthus observations of workers led Charles Darwin to propose the theory of natural selection in his book “Origin of Species”. The theory of natural selection is based on following points:

1. Rapid Multiplication: Every organism has enormous ability to reproduce to continuance of the species. All animals and plant tend to multiply in geometrical progression. For example, an organism will be double in Ist year, four times by 2nd yr and 8 times in a third year and so on. Lets see few example of organism to understand the potential of organism to multiply. These examples are as follows:  

(i) Paramecium: it has multiplication rate of 3 times in 48 hrs. if single paramecium will allow to grow and multiply in 5 yrs to give the mass equal to ten thousand times the size of earth. 

(ii) Cod Fishes: Cod fish produces over 1 million eggs in a year. If all these eggs will rise to fishes, the whole atlantic ocean will be filled in next 5 yrs.

(iii) Oyester: An Oyester may lay 114,000,000 eggs at a single spawning. If all the oyster grow and survived upto adulthood for 5 generations, then number of oyster will be more than the number of electrons in the universe. 

(iv) Elephant: Elephant has an average life span of 90 years and during the whole life span he can produce only six offsprings. If all the offsprings survived, single elephant pair would produce 19,000,000 elephants in 750 years.

(v) Plants: Plants produces thousands of seeds every year.  

2. Limited natural resources: Inspite the enormous capacity of an organism to reproduce, the number of individual species remain constant. It is due to increase in population in animal or plant requires more space and food. Ultimately the food to plant or animal is provided by the CO2 from air, water and mineral from soil. The amount of thes basic material is limited in universe. Hence, it does not allow the population of organism beyond the limit and an equilibrium is reached.