Class 12 Biology CH 7 Evolution

Class 12 Biology CH 7 Evolution

Q1. Explain antibiotic, resistance observed in bacteria in light of Darwinian selection theory.

Ans: According to Darwin, the environment selects organisms with favorable variations and these organisms are allowed to survive. When a bacterial population encounters a particular antibiotic, those sensitive to it die. But some bacteria having mutations become resistant to the antibiotic. Such resistant bacteria survive and multiply quickly as the competing bacteria have died. Some of the resistance-providing genes become widespread and the entire bacterial population becomes resistant.

Q2. Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution

Ans – Do it yourself

Q3. Attempt to give a clear definition of the term species.

Ans- Species is a group or population of individuals having the potential to interbreed and produce sustainable and fertile offspring.

Q4. Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)


Ancestors in human evolution

Brain size


Skeletal features

Dietary preferences



Large brain (size unknown)

Large canines and incisors, square molars

  • Arms and legs of the same length.
  • Arboreal, knuckle-walker.

Soft fruits and leaves



Small brain (size unknown)

Small canines, flattened molars

  • Walked erect on the feet.
  • Had a short face.

Hard nuts and seeds

Australopithecus afarensis


500 cm3

Small canines and incisors

  • About 1.05 meters high.
  • Mainly a terrestrial creature with bipedal locomotion.

Mostly fruits and leaves rather than seeds and other hard plant material

Australopithecus africanus

350–450 cm3

Small canines

  • Low forehead, protruding face, lack of chin.
  • Probably not taller than 4 feet but walked upright.

Essentially fruits but hunted with stones

Homo habilis

650–800 cm3

Small canines

  • About 1.5−1.8 meters tall.
  • Bipedal and moved erect.

Probably did not eat meat

Homo erectus

800–1,200 cm3

Small canines

  • About 5.5 feet tall with a bowl-shaped pelvis.
  • The foot was arched to support body weight, and the grasping ability of the foot was completely lost.

Probably ate meat

Homo neanderthalensis

1,400 cm3

Heavier than modern teeth, wisdom teeth

  • Flat cranium, sloping forehead, no chin.


Homo sapiens fossils

1650 cm3

Teeth closer together, wisdom teeth

  • Large skull, high forehead.
  • Prominent chin and broad flat face.
  • Sturdy body and less hair.

Ate both plants and animals

Homo sapiens sapiens

1,500 cm3

Strong jaws with teeth closer together, wisdom teeth

  • A slight raising of the skull cap.
  • Thinning of skull bones.

Ate both plants and animals

Q5. Find out through the internet and popular science articles whether animals other than man have self-consciousness.

Ans: Recent studies on self-consciousness says gibbons are the nearest to human in this respect. Apes and orangutans came next. Among domestic animals, dogs and other members of the Canidae family show subtle self-consciousness.

Q6. List 10 modern-day animals and using the” internet resources link them to a corresponding ancient fossil. Name both.


The list is as follows:

Name of the animal Name of the fossil
Horse Eohippus
Man Ramapithecus
Elephant Moerithers
Whale Protocetus
Fish Arandaspis
Giraffe Palaeotragus
Dog Leptocyon
Camel Protylopus
Tetrapods Icthyospega
Bat Archaeonycteris

Q7. Practise drawing various animals and plants.

Ans-  Do Yourself.

Q8.Describe one example of adaptive radiation.

Ans- Adaptive radiation is a process of divergent evolution in which members of the same ancestral species of a large taxonomic group are evolved along different lines in different habitats of the same geographical area.

Darwin’s finches of the Galápagos Islands exhibiting a variety of beaks are an example of adaptive radiation. Darwin reported that finches found on different islands of the Galápagos Islands with varied environmental conditions differed with respect to bill size and shape due to different feeding habits. However, they were closely related to one another and had evolved from a common ancestral seed-eating ground finch living in a particular geographical area of the South American mainland. Later, these finches radiated to different geographical areas and adapted differently in their feeding habits, developing different kinds of beaks.

Q9. Can we call human evolution as adaptive radiation?

Ans- No, we cannot call human evolution adaptive radiation. In human evolution, brain size, skeletal structure, dietary preference, and social and cultural evolution occurred, while in adaptive radiation, the origin, basic structure, and development of the organs remain the same, only morphological changes occur.

Q10. Using various resources such as your school library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal say a horse.

Ans: Evolutionary stages of horse:
Eohippus – Mesohippus – Merychippus – Pliohippus – Equus.
Evolutionary trend:
(i) Increase in body size.
(ii) Elongation of the neck.
(iii) Lengthening of limbs.
(iv) Enlargement of the third digit.
(v) Increase in structural complexity of teeth for feeding on grass.

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