NCERT Solutions for class 12th Biology Chapter 7 Evolution


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

Sol. According to Darwinian selection theory, the organisms with the important characteristic features that enable them to survive better in natural conditions (the existing environmental conditions) would eliminate the others organisms that are less-endowed to survive under those conditions.

An example of such selection is antibiotic resistance in bacteria. Bacteria have been subjected to antibiotics since the earliest discovery of the first antibiotic i.e. Penicillin. When these bacterial populations are grown in culture containing antibiotic penicillin, the colonies that were sensitive to penicillin died, whereas one or few bacterial colonies that were resistant to penicillin survived. Only the ones that survived the antibiotic treatment could further perpetuate and produce off springs, resulting in the increase of antibiotic resistance in the bacterial population.

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.


  • According to Darwinian selection theory, bacteria can acquire resistance in two ways: either through a new genetic change that helps the bacte­rium survives, or by getting DNA from a bacterium that is already resistant.
  • The use of antibiotics or drugs against eukaryotic organism has resulted in the selection of resistant varieties in much lesser time. There are examples of evolution by anthropogenic action.

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

Sol. • New fossil discovered : Palaeontologists from Hokkaido University in Japan, in cooperation with palaeontologists from the Perot Museum of Nature and Science in Dallas, Texas, have discovered the first-confirmed occurrence of a lambeosaurine (crested ‘duck-billed’ dinosaur) from the Arctic – part of the skull of a lambeosaurine dinosaur from the Liscomb Bonebed (71-68 Ma) found on Alaska’s North Slope.

The discovery proves for the first time that lambeosaurines inhabited the Arctic during the Late Cretaceous. In addition, the numeric abundance of hadrosaurine fossils compared to the lambeosaurine fossils in the marine­ influenced environment of the Liscomb Bonebed suggests the possibility that hadrosaurines and lambeosaurines had different habitat preferences. A fossil of human was discovered in Israel. This fossil has been named as Misliya-1; after the cave in which it was found. Previously scientists believed that Homo sapiens left Africa around 100,000 years ago. But this fossil makes the scientists estimate that Homo sapiens may have left Africa about 175,000 to 200,000 years ago.

Controversies about evolution

  • Huxley proposed that man evolved from the apes but paleontological evidences revealed that man and apes had common ancestry.
  • Earlier the spermatophytes were considered to be the first seed­ bearing plants but the fossil studies have shown that Pteridosperms (seed ferns) were first land plants to develop seed habit. These act as missing link between the Ferns and Gymnosperms.


  • This new discovery of lambeosaurine (crested ‘duck-billed’ dinosaur) exemplifies the geographic link between lambeosaurines of North America and the Far East.
  • Part of a jawbone found in Misliya, Israel, has been identified as the oldest human fossil found outside Africa.

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

Sol. Species is population or group of individuals that have potential of interbreeding in order to produce viable, fertile young ones but are reproductively isolated from members of other species.

Question 5. Find out through internet and popular science articles whether animals other than man has self-consciousness.

Sol. There are many animals other than humans which have self consciousness. Self consciousness may be defined as aware of oneself as an individual. Recent studies on self consciousness says that dolphin is the best example that have self consciousness like man. Recognising oneself in a mirror is an indicator of self awareness.

Because, dolphins are highly intelligent mammals. They have a sense of self and they also recognize others among themselves and others. They exhibit intimacy and chemistry with their partners and communicate with through various body gestures including whistles, tail-slapping, and other body movements.

Not only dolphins but there are some other animals also such as Chimpanzees, Bottlenose dolphins, Gorillas, Orcas and even elephants which have been observed to show variable levels of self-consciousness. Apes, like the human beings, have well developed facial muscles for showing facial gestures and also have property of self-consciousness.

Note: Self consciousness is the ability to introspect and identify self from the others. It is checked through various techniques and one such is mirror test in which many animals including Dolphins passed.

Question 6. List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.

Question 7. Practice drawing various animals and plants.

Question 8. Describe one example of adaptive radiation.

Sol. Adaptive radiation is an evolutionary process that produces new species from a single, rapidly diversifying lineage. This process occurs due to natural selection. An example of adaptive radiation is Darwin finches, found in Galapagos Island.

A large variety of finches is present in Galapagos Island that arose from a single species, which reached this land accidentally. As a result, many new species have evolved, diverged, and adapted to occupy new habitats. These finches have developed different eating habits and different types of beaks to suit their feeding habits. The insectivorous, blood-sucking, and other species of finches with varied dietary habits have evolved from a single seed-eating finch ancestor.

Darwin’s finches of the Galapagos islands had common ancestors but now have different types of modified beaks according to their food habits.

Question 9. Can we call human evolution adaptive radiation?


  • No, we cannot call human evolution as adaptive radiation.
  • 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 is a process of change by which people originated from apelike ancestors. It represents an example of anagenesis (= species formation without branching of the evolutionary line of descent).


  • Hominid introduction occurred in Africa and Asia.
  • Homo habilis lived in Africa – 2 million years ago.
  • Homo erectus- migrated to Asia and Europe and diverged into 2 species -Java Man and Peking Man.
  • Similarly Homo erectus – was followed by Homo sapiens.
  • Primitive Neanderthal man in Europe gave way to African cro-magnon

Question 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.

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

  • 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 evolutionary stages of horse is represented as follow:
    • Hyracotherium or Eohippus: They are also called dawn horse.
    • The evolution of horse started with eohippus. It had a short head and neck and four functional toes with 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 (Intermediate horse): It was slightly taller than Eohippus. It had three toes in each foot. Fossil of mesohippus are found in the early and middle oligocene of North America. It also had a larger brain.
    • 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. This horse was about the size of a fox terrier.

Note: Horse fossils have been found in sedimentary strata at the beginning of the Tertiary period during a time-span called the Eocene (approximately 50 million years ago, according to uniformitarian dating). They are usually labelled Eohippus or Hyracotherium.

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