Biology Class 12 NCERT Solutions: Chapter 7 Evolution Part 3

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Q.9 Can we call human evolution as adaptive radiation?


  • No, human evolution cannot be called adaptive radiation. This is because adaptive radiation is an evolutionary process that produces new species from a single, rapidly diversifying lineage, which is not the case with human evolution.

  • Human evolution is a gradual process that took place slowly in time. It represents an example of anagenesis.

Q.10 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 horse.


  • The evolution of horse started with Eohippus during Eocene period. It involved the following evolutionary stages.

    • Gradual increase in body size

    • Elongation of head and neck region

    • Increase in the length of limbs and feet

    • Gradual reduction of lateral digits

    • Enlargement of third functional toe

    • Strengthening of the back

    • Development of brain and sensory organs

    • Increase in the complexity of teeth for feeding on grass

    • The evolution of horse is represented as

      Image of Evolution of Horse

      Image of Evolution of Horse

  • Eohippus

    • It had a short head and neck. It had four functional toes and a splint of 1 and 5 on each hind limb and a splint of 1 and 3 in each forelimb.

    • The molars were short crowned that were adapted for grinding the plant diet.

  • Mesohippus

    • It was slightly taller than Eohippus. It had three toes in each foot.

  • Merychippus

    • It had the size of approximately 100 cm. Although it still had three toes in each foot, but it could run on one toe.

    • The side toe did not touch the ground. The molars were adapted for chewing the grass.

  • Pliohippus

    • It resembled the modern horse and was around 108 cm tall. It had a single functional toe with splint of 2nd and 4th in each limb.

  • Equus

    • Pliohippus gave rise to Equus or the modern horse with one toe in each foot. They have incisors for cutting grass and molars for grinding food.

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