Biology Class 12 NCERT Solutions: Chapter 7 Evolution Part 1 (For CBSE, ICSE, IAS, NET, NRA 2023)

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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
NameBrain CapacityPostureFoodFeatures
1.Dryopithec us AfricansKnuckle walker, walked similar and chimpanzees (was more ape-like)Soft fruit and leavesCanines large, arms and legs are of equal size
2.Ramapithe cus-


Semi-erect (more man-like)Seeds, nutsCanines were small while molars were large.
3.Australopithecus AfricanusFull erect posture, height (1.05 m)Herbivorous (ate fruits)Hunted with stone weapons, lived at trees, canines and incisors were small
4.Homo habilisFull erect posture, height (1.5 m)CarnivorousCanines were small. They were first tool makers.
5.Homo erectus

Full erect posture, height (1.51. 8 m)OmnivorousThey used stone and bone tools for hunting games.
6.Homo neanderthalnsis

Full erect posture, height (1.5 - 1.66 m)OmnivorousCave dwellers, used hides to protect their bodies, and buried their dead
7.Homo sapiens fossilisFully erect posture with height (1.8 m)OmnivorousThey 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.
8.Homo sapiens sapiens

Fully erect posture height (1.5 - 1.8 m)OmnivorousThey are the living modern men, with high intelligence. They developed art, culture, language, speech, etc. They cultivated crops and domesticated animals