Evolution for Class 10: Darwin’s Theory Explained Simply

How can a small change in colour decide whether a beetle lives or dies? That one question holds the whole idea of evolution. Nobody plans it, and no organism wishes for it. It happens because living things differ from one another, and the surroundings favour some differences over others.

This guide explains Darwin’s theory with a simple beetle colony, shows how new species form, and lists the evidence you can actually check. It also states clearly where this chapter stands: the evolution portion of Heredity and Evolution is part of the Karnataka SSLC syllabus, while CBSE has removed it from Class 10 and the topic returns in Class 12 Biology.

A Beetle Colony and the Birth of an Idea

Imagine a colony of red beetles living on green bushes, with crows that eat beetles. Three small events show how evolution works.

The definition to remember

Evolution is the change in the inherited characteristics of a population over many generations. Notice what is doing the work: variation that arises during reproduction, surroundings that favour some variations, and time. You can read more about how variation accumulates during reproduction.

Darwin’s Theory in Four Steps

Charles Darwin proposed natural selection after years of observing living things. His idea fits in four steps.

1. Variation. Individuals in a population differ from one another in many small ways.
2. Struggle for existence. Organisms produce more young than the food, water and space available can support, so they compete.
3. Natural selection. Individuals with traits that suit their surroundings are more likely to survive and reproduce.
4. Inheritance and accumulation. Those useful traits are passed on, and over many generations they build up, so the population changes.

“Survival of the fittest” does not mean the strongest. It means the best suited to the surroundings, which in the beetle colony meant the green ones.

Acquired and inherited traits

Only some changes are passed on, and Class 10 questions often test the difference.

The rule: only changes in the DNA of the reproductive cells can be inherited, so only they can drive evolution. For the genetics behind this, see the Mendel’s laws of inheritance notes.

From Variation to New Species

How speciation happens

A new species forms when two populations become so different that they can no longer interbreed and produce fertile young. The usual route has four steps:

1. A population is split by a barrier such as a mountain, a river or a stretch of sea. This is geographical isolation.
2. The two groups face different surroundings, and chance events affect each one differently.
3. Variations accumulate separately in each group, through natural selection and genetic drift.
4. After many generations, the groups are so different that they can no longer interbreed, and two species exist where there was one.

Selection by people: the wild cabbage

Humans have also shaped living things by choosing which ones to breed. This is called artificial selection. From one wild cabbage plant, farmers selected different features over many generations:

• Large leaves gave the cabbage.
• Arrested flower development gave broccoli.
• Sterile flowers gave cauliflower.
• A swollen stem gave kohlrabi.
• Larger, curly leaves gave kale.

If human choice can produce such different vegetables over the history of farming, then nature’s selection over millions of years can do far more. For a wider look at the topic, see this piece on evolution, variation and traits.

Evidence You Can Check: Organs and Fossils

Homologous and analogous organs

Scientists compare body parts to work out how closely living things are related.

Fossils

Fossils are the preserved remains or impressions of organisms that lived long ago. Layers of rock form over time, so fossils found in deeper layers are generally older than those found closer to the surface. Scientists can also estimate age by measuring the ratio of different isotopes of an element, such as carbon, in the fossil material.

Fossils that tell a story

• Feathers: some dinosaurs had feathers, probably for warmth. Birds later used feathers for flight. A structure can therefore be put to a new use over time.
• Archaeopteryx: this fossil has feathers like a bird but teeth and a tail like a reptile, which suggests that birds are related to reptiles.

These lines of evidence agree with one another, and that agreement is what makes the theory convincing.

Misunderstandings and Where the Chapter Stands

Four common misunderstandings

• Organisms do not evolve because they “want” or “need” to. Variation arises first, and the surroundings then select.
• “Fittest” does not mean strongest. It means best suited to the surroundings.
• Homologous and analogous organs are different ideas. Homologous means same origin, and analogous means same function.
• Humans did not evolve from chimpanzees. Humans and chimpanzees share a common ancestor.

Where this chapter stands

Frequently Asked Questions

Q1. What is Darwin’s theory of natural selection?

It says that individuals in a population vary, that they compete for limited resources, and that those with traits better suited to their surroundings survive and reproduce more. Their useful traits are passed on and build up over generations, so the population changes.

Q2. What is the difference between acquired and inherited traits?

Inherited traits are controlled by genes passed on through reproductive cells, such as eye colour. Acquired traits develop during a lifetime, such as muscles built by exercise, and are not passed on to offspring.

Q3. What are homologous and analogous organs?

Homologous organs have the same basic structure and origin but may do different jobs, like the forelimbs of a human and a bat. Analogous organs do the same job but have different structure and origin, like the wings of a bat and a bird.

Q4. How do new species form?

A population is usually split by a barrier, which is called geographical isolation. Each group then accumulates different variations through natural selection and genetic drift until the two can no longer interbreed.

Q5. Did humans evolve from monkeys?

No. Humans, apes and monkeys share common ancestors that lived millions of years ago. Evolution produced several branches from those ancestors, and humans are one of them, so no living species is the ancestor of another.

Small Differences, Long Timelines

Evolution is not a story about progress or effort. It is a story about small differences, repeated over very long times, in surroundings that favour some differences over others. Hold on to the beetle colony, and the definitions, the evidence and the exam answers will all follow from it.