Darwin's finches: one ancestor, many beaks.

A seed-eating ancestor spreading across islands with different food; beak shape evolves to fit each.

Radiate the ancestor into three distinct beak types from one start.

Thinking adaptive radiation needs many ancestors.

• 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).

Teaching this idea? Put the simulation on your own page or LMS with this code.