Adaptive Radiation (NCERT Class 12 Biology)

Definition:
Adaptive radiation is the evolution of different species from a common ancestor within a geographical area, where each species becomes adapted to a different habitat or ecological niche.

NCERT Definition:

The process of evolution of different species in a given geographical area starting from a common ancestor and radiating into different habitats is called adaptive radiation.

Characteristics of Adaptive Radiation

  • Begins with a common ancestral species.
  • Occurs in an isolated geographical region (e.g., islands or continents).
  • Different populations adapt to different ecological niches.
  • Results in the formation of many closely related species.

Example 1: Darwin’s Finches (Galápagos Islands)

Darwin observed several species of finches on the Galápagos Islands.

  • All evolved from a common seed-eating ancestor.
  • Different species developed different types of beaks according to their food habits.
Finch TypeAdaptation
Seed-eatingThick, strong beak
Insect-eatingThin, pointed beak
Cactus-feedingLong beak
VegetarianBroad beak

Reason: Different food resources in different habitats led to natural selection.

Example 2: Australian Marsupials

Australia was geographically isolated.

From a common marsupial ancestor, many different marsupials evolved:

  • Kangaroo
  • Koala
  • Wombat
  • Bandicoot
  • Sugar glider
  • Tasmanian wolf
  • Marsupial mole
  • Marsupial rat

Each occupies a different ecological niche.

This is another classic example of adaptive radiation.

Adaptive Radiation and Convergent Evolution

Australia also has placental mammals that resemble marsupials but evolved independently.

Examples:

Placental MammalAustralian Marsupial
MoleMarsupial mole
AnteaterNumbat (banded anteater)
MouseMarsupial mouse
Flying squirrelFlying phalanger (sugar glider)
WolfTasmanian wolf

Although they look alike, they do not share a recent common ancestor for these traits.

This similarity is due to convergent evolution, where unrelated organisms evolve similar adaptations because they live in similar environments.

Difference Between Adaptive Radiation and Convergent Evolution

Adaptive RadiationConvergent Evolution
One ancestor gives rise to many speciesDifferent ancestors evolve similar features
Produces divergent evolutionProduces analogous similarities
Species are closely relatedSpecies are distantly related
Example: Darwin’s finchesPlacental wolf and Tasmanian wolf

Flow Chart (Easy to Remember)

Common Ancestor
       │
       ▼
Different habitats
       │
Natural Selection
       │
Different adaptations
       │
Formation of new species
       │
Adaptive Radiation

NCERT Exam Points

  • Adaptive radiation = Evolution of many species from one common ancestor in a geographical area.
  • Darwin’s finches and Australian marsupials are classic examples.
  • Placental mammals and Australian marsupials demonstrate convergent evolution, as unrelated groups independently evolved similar adaptations.

Memory Trick

Convergent Evolution = Many → Similar

Adaptive Radiation = One → Many

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