Branching descent and natural selection are the two key concepts of Darwinian theory of evolution. Explain each concept with the help of a suitable example.
Answers
Branching descent :
Different species descending from the common ancestor - get adapted in different habitats.
e.g., Darwins finches - varieties of finches arose from grain eaters/Australian marsupials-evolved from common marsupial.
Natural selection :
A process in which heritable variations enable better survival of a species to reproduce in large number.
e.g. White moth surviving before the industrial revolution and black moth surviving after industrial revolution/ Long necked giraffe survived/DDT resistant mosquito survive.
The theory of natural selection proposed by Darwin in the year 1859 (Darwinism) : This theory states that the organisms evolution through natural selection and accumulation of inheritable variations.
Some of the features of the theory are :-
1. Limited food and space:- continuous consumption of food causes scarcity and even population of different species cannot increase their consumption beyond a certain limit.
2. Struggle for existence:- It is said, “Survival of the fittest”. So there are always competition going on among organisms for resources.
3. Variations:- New species arrive when there are variations such as in structure, size and physiology.
4. Inheritance of useful variations:- Next generation acquires the same process to get variations and natural selection. And formation of new variations by accumulations completely produces new species.