Lesson 7 of 13 · 6 min
Adaptive radiation
NCERT §6.4
Next to a globe, Ms Fatima shows drawings of small black birds whose beaks look nothing alike. 'All from the same islands,' she says. 'Guess where they came from.'
The lesson in notes
In short
On his voyage Darwin visited the Galapagos Islands and saw an amazing diversity of creatures, above all small black birds later called Darwin's finches.
Many varieties of finch lived on the same island. Darwin conjectured that all evolved on the island itself.
From the original seed-eating form, others with altered beaks arose, letting them become insectivorous and vegetarian finches.
Adaptive radiation: the evolution of different species in one geographical area, starting from one point and radiating out into other habitats. Darwin's finches are the textbook example.
Australian marsupials are another: many different marsupials evolved from one ancestral stock, all within the Australian island continent.
When more than one adaptive radiation seems to have taken place in an isolated area (in different habitats), it can be called convergent evolution.
Placental mammals in Australia also radiated into forms that each look similar to a matching marsupial, for example the placental wolf and the Tasmanian wolf (a marsupial).