NCERT Solutions for Class 12 Biology Chapter 6 – Evolution

Q.1) Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.

Ans: According to Darwin’s theory of natural selection, individuals with favourable inheritable variations survive and reproduce more successfully. In a bacterial population, some bacteria already possess genetic variations that make them resistant to antibiotics. When antibiotics are applied, sensitive bacteria die while resistant ones survive and multiply. Over generations, the population becomes dominated by antibiotic-resistant bacteria.

Q.2) Find out any new fossil discoveries or controversies about evolution.

Ans: Fossils provide important evidence of evolution. Some notable examples include:

• The discovery of a nearly complete early human skull in Dmanisi, Georgia, suggesting a single evolving Homo lineage spreading out of Africa.
• Reclassification of Archaeopteryx as a feathered dinosaur based on newly discovered fossils in China.

Q.3) Define the term species.

Ans: A species is a group of organisms that can interbreed naturally and produce fertile offspring, and are reproductively isolated from other such groups.

Q.4) Trace the major components of human evolution.

Ans: Human evolution involved gradual changes in brain size, posture, skeletal structure and diet. Important stages include:

• Dryopithecus: Ape-like ancestor, knuckle-walking, fruit eater.
• Ramapithecus: Semi-erect posture, herbivorous.
• Australopithecines: Upright posture, increased brain size.
• Homo habilis: Tool maker, improved brain capacity.
• Homo erectus: Fully erect posture, use of tools.
• Neanderthal man: Large brain, cave dweller.
• Homo sapiens: Modern humans with high intelligence and culture.

Q.5) Do animals other than humans show self-consciousness?

Ans: Yes. A few animals have shown self-awareness through mirror tests. These include chimpanzees, gorillas, orangutans, dolphins, elephants, magpies, bonobos and rhesus macaques.

Q.6) List ten modern animals with their corresponding ancient fossils.

• Dog – Leptocyon
• Horse – Eohippus
• Elephant – Mastodon
• Crocodile – Protosuchus
• Bird – Archaeopteryx
• Camel – Protylopus
• Whale – Protocetus
• Fish – Ostracoderms
• Giraffe – Palaeotragus
• Crocodile – Sarcosuchus

Q.7) Describe one example of adaptive radiation.

Ans: Darwin’s finches of the Galapagos Islands are a classic example of adaptive radiation. All finches evolved from a common ancestor but developed different beak shapes to adapt to different food sources.

Q.8) Can human evolution be called adaptive radiation?

Ans: No. Human evolution is an example of anagenesis, involving gradual changes over time, not rapid diversification into multiple species.

Q.9) Trace the evolutionary stages of the horse.

Ans: Horse evolution shows increase in body size, reduction in toes, strengthening of limbs and development of grinding teeth. The lineage progressed from Eohippus to Miohippus, Merychippus, Pliohippus and finally modern Equus.

Q.10) Practise drawing animals and plants.

Ans: Students are advised to practise neat, labelled diagrams of commonly studied animals and plants such as goat and banana tree to improve exam performance.