Evolution of life forms: Darwin’s theory

How did life forms come to be so diverse?

In plain words: species were not made once and for all. Living things vary, the variants that survive and reproduce best leave more offspring, and over very long times this changes populations into new kinds of organisms.

The theory of special creation

NCERT summarises a historical special-creation account using three claims; this is not a description of every religious tradition or a scientific estimate of Earth’s age (page 112):

1. all living organisms (species or types) that we see today were created as such;
2. the diversity was always the same since creation and will be the same in future;
3. the earth is about 4000 years old.

All three ideas were strongly challenged during the nineteenth century (page 112).

Darwin’s voyage and his conclusions

• Many life forms that existed millions of years ago do not exist any more: there have been extinctions, just as new forms of life arose at different periods of the earth’s history (page 112).
• Any population has built-in variation in its characteristics. Heritable characteristics affecting survival or reproduction in a particular environment can change relative reproductive success; advantageous variants tend to contribute more descendants over generations (pages 112–113).

Fitness and natural selection

The fitness, according to Darwin, refers ultimately and only to reproductive fitness.

NCERT Biology (Class 12), Section 6.2, page 113

• Those who are better fit in an environment leave more progeny than others. Survival matters insofar as it contributes to reproduction; greater survival is not required in every case of higher reproductive success. Darwin called this natural selection and implied it as a mechanism of evolution (page 113).
• Alfred Wallace, a naturalist who worked in the Malay Archipelago, had come to similar conclusions around the same time (page 113).
• In due course, apparently new types of organisms become recognisable. All existing life forms share similarities and share common ancestors, which lived at different periods of the earth’s history (epochs, periods and eras) (page 113).
• The geological history of the earth closely correlates with its biological history. A common permissible conclusion is that the earth is very old: not thousands of years, as was thought earlier, but billions of years (page 113).

Solved examples

Common mistakes to avoid

Quick revision summary

• Special creation: organisms created as such; diversity unchanged since creation; earth about 4000 years old. All three were challenged in the nineteenth century.
• Darwin (voyage on H.M.S. Beagle): living forms share similarities with each other and with forms of millions of years ago; extinctions and new forms; gradual evolution.
• Populations have built-in variation; the better fit leave more progeny and are selected by nature: natural selection, a mechanism of evolution. Fitness is reproductive fitness.
• Alfred Wallace (Malay Archipelago) reached similar conclusions. Life forms share common ancestors; the earth is billions of years old.

Questions students ask

Is Darwin’s theory of evolution still in NCERT and the NEET (UG) 2026 syllabus?

Yes, Darwin’s theory of evolution is still taught in NCERT Class 12 Biology: Chapter 6, Evolution, of the 2026–27 reprint covers his conclusions, reproductive fitness and natural selection (NCERT Section 6.2, pages 112–113) and returns to his theory in Sections 6.5 and 6.6 (pages 118–119). The NEET (UG) 2026 syllabus, Unit 7 (Genetics and Evolution), lists under Evolution “Darwin’s contribution, Modern Synthetic theory of Evolution” and “Natural Selection with examples, types of natural selection”. The 2026–27 chapter itself never names the modern synthetic theory, though the syllabus does.

Is natural selection the same as survival of the fittest?

Beyond the NCERT text, natural selection and survival of the fittest are two names for the same principle in Darwin’s own usage: in the sixth edition of On the Origin of Species (1872) he headed Chapter IV “Natural Selection; or the Survival of the Fittest”. In Chapter III he wrote that he had called the principle natural selection, and that “the expression often used by Mr. Herbert Spencer, of the Survival of the Fittest, is more accurate, and is sometimes equally convenient” (public-domain text, Project Gutenberg). So the phrase, which Darwin credited to Spencer, names the same idea and is not a separate theory.

When did Darwin and Wallace publish the theory of natural selection?

Beyond the NCERT text, Darwin and Wallace first published natural selection together in 1858: Darwin’s autobiography records that Wallace sent him an essay early that summer which “contained exactly the same theory as mine”, and that it appeared with an abstract of Darwin’s manuscript in the Journal of the Proceedings of the Linnean Society, 1858. Darwin’s book On the Origin of Species followed in November 1859 (both from the public-domain text, Project Gutenberg). NCERT gives no dates for either (pages 112–113).

What is the difference between natural selection and artificial selection?

In natural selection nature does the choosing, while in artificial selection people choose which plants and animals breed: NCERT says that those better fit in an environment leave more progeny than others (page 113), whereas man has bred selected plants and animals for agriculture, horticulture, sport or security (page 115; see artificial selection). NCERT describes the second without using the term artificial selection. Beyond the NCERT text, Darwin chose the name natural selection “in order to mark its relation to man’s power of selection” (On the Origin of Species, sixth edition, 1872, public domain).

Practice questions

Try each question first, then open the answer to check your working.

1. Q1. In which ship did Darwin make the voyage on which his conclusions were based?

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   H.M.S. Beagle, a sail ship that went round the world (NCERT page 112).

2. Q2. What did Darwin call the process by which the better fit are selected by nature?

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   Natural selection, which he implied as a mechanism of evolution (NCERT page 113).

3. Q3. According to the theory of special creation, how old is the earth?

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   About 4000 years (NCERT page 112).