Question

Q1. Will two species close enough to be classified under one group if they have analogous organs. Give reasons?

Q2. What different strategus are used by different species for determining gender?

Q3. Explain origin of species based on the theory of natural selection?

Answer 1

NO. Organising in the same group will have similar body designs. They have a lot of similarities. Analogous organs are those which have different body designs but perform same functions.
So organising in same group will have similar body designs and hence cannot have analogous organs

In some organisims gender is determined by sex chromosomes. In some organisims environment plays an important role like temperature, etc.

Species have evolved due to the variation caused by natural selection.
Changes in the environment exerts changes/ variations in the organisms. These variations continue to develop and will ultimately lead to formation of a species.

Answer 2

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.