Biology Class 12 NCERT Solutions: Chapter 7 Evolution Part 1

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


  • Darwinian selection theory states that individuals with favourable variations are better adapted than individuals with less favourable variation.

  • It means that nature selects the individuals with useful variation as these individuals are better evolved to survive in the existing environment.

  • An example of such selection is antibiotic resistance in bacteria.

  • When bacterial population was grown on an agar plate containing antibiotic penicillin, the colonies that were sensitive to penicillin died, whereas one or few bacterial colonies that were resistant to penicillin survived.

  • This is because these bacteria had undergone chance mutation, which resulted in the evolution of a gene that made them resistant to penicillin drug.

  • Hence, the resistant bacteria multiplied quickly as compared to non-resistant (sensitive) bacteria, thereby increasing their number.

  • Hence, the advantage of an individual over other helps in the struggle for existence.

Q.2 Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.


  • Fossils of dinosaurs have revealed the evolution of reptiles in Jurassic period. As a result of this, evolution of other animals such as birds and mammals has also been discovered.

  • However, two unusual fossils recently unearthed in China have ignited a controversy over the evolution of birds.

  • Confuciusornis is one such genus of primitive birds that were crow sized and lived during the Cretaceous period in China.

Q.3 Attempt giving a clear definition of the term species


  • Species can be defined as a group of organisms, which have the capability to interbreed in order to produce fertile offspring.

Q.4 Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)


The various components of human evolution are as follows.

(i) Brain capacity

(ii) Posture

(iii) Food / dietary preference

(iv) Other important features

Table of Human Evolution


Brain Capacity





Dryopithec us Africans


Knuckle walker, walked similar and chimpanzees (was more ape-like)

Soft fruit and leaves

Canines large, arms and legs are of equal size


Ramapithe cus



Semi-erect (more man-like)

Seeds, nuts

Canines were small while molars were large.


Australopithecus Africanus

Full erect posture, height (1.05 m)

Herbivorous (ate fruits)

Hunted with stone weapons, lived at trees, canines and incisors were small


Homo habilis

Full erect posture, height (1.5 m)


Canines were small. They were first tool makers.


Homo erectus

Full erect posture, height (1.51.8 m)


They used stone and bone tools for hunting games.


Homo neanderthalnsis

Full erect posture, height (1.5-1.66 m)


Cave dwellers, used hides to protect their bodies, and buried their dead


Homo sapiens fossilis

Fully erect posture with height (1.8 m)


They had strong jaw with teeth close together. They were cave dwellers, made paintings and carvings in the caves. They developed a culture and were called first modern men.


Homo sapiens sapiens

Fully erect posture height (1.5-1.8 m)


They are the living modern men, with high intelligence. They developed art, culture, language, speech, etc. They cultivated crops and domesticated animals