medium difficulty6 min

Natural Selection

Natural selection is the process in which organisms with useful variations survive and reproduce more successfully in a particular environment.

In one line: Nature keeps the trait that helps survival.

Practice This Concept

Understand it

Natural selection acts on variation.
In any population, some organisms have features that help them survive better in a given environment.
These organisms are more likely to live long enough to reproduce and pass the helpful traits to the next generation.
Over many generations, the useful trait becomes more common in the population.

Example

If darker insects are better hidden from birds on dark tree bark, they survive more often and produce more young with the same feature. This is natural selection.

Rule to remember

Natural selection favours variations that improve survival and reproduction in a given environment.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1In a habitat with dark tree bark, darker insects are less easily seen by birds.
2More dark insects survive, more of them reproduce, and their trait becomes common in later generations.

Method you can reuse

1Identify the variation in the population.
2Check which variation helps survival.
3Note that better-suited organisms survive and reproduce more.
4Track the trait over generations.
5State that the useful trait becomes more common.

Visual tip

A before-and-after population sketch or a simple survival chart helps show how one trait becomes common over generations.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why do helpful traits become more common in a population over time?

Think first, then show answer

Helpful traits become more common because organisms with those traits survive and reproduce more successfully. Natural selection keeps the useful trait in the population for future generations.

Common wrong answer

A common wrong answer is to say all organisms in a population change together at once. Natural selection works through differential survival and reproduction over generations.

Don't mix this up

Students sometimes think individual organisms change their traits because they need to survive. That is wrong; selection happens across generations, not by instant change in one individual.

Exam tip

When the question mentions better survival and more offspring over time, connect the answer to natural selection.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Explain why a particular trait increases in a population, or describe the role of survival and reproduction in evolution.

1
Enough for 1 mark
Natural selection is the process in which organisms with useful variations survive and reproduce more successfully in a particular environment.
2
Add for 2 marks
Example: If darker insects are better hidden from birds on dark tree bark, they survive more often and produce more young with the same feature. This is natural selection.
3
Add for 3 marks
In any population, some organisms have features that help them survive better in a given environment.

MCQ Quiz

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