Question

Common in Darwin’s finches and Australian marsupials is:

• A. They are all extinct.
• B. They show adaptive radiation.
• C. They have homologous organs.
• D. They are all found in South America.

Hint:

Remember that when more than one adaptive radiation occurs in an isolated geographical area (representing different ancestral stocks), it results in convergent evolution.
For example, the placental wolf and the Tasmanian wolf (marsupial) show striking similarities due to convergent evolution, though each arose from its own separate adaptive radiation.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
This question is from the chapter "Evolution" in the NCERT Class 12 biology curriculum.
We need to identify the evolutionary phenomenon that is a common feature of both Darwin's finches and Australian marsupials.

Step 2: Key Concept or Approach:
Adaptive radiation is an evolutionary process in which a single ancestral species rapidly diversifies into a multitude of new forms, particularly when a change in the environment opens new ecological niches, resources, or geographical habitats.

Step 3: Detailed Explanation:

• Let us analyze how both groups exhibit this phenomenon:
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Darwin's Finches: On the isolated Galapagos Islands, Darwin observed many species of finches. All of these species evolved on the islands from a single ancestral seed-eating finch that arrived from the mainland of South America. Over time, they adapted to different feeding niches, developing variations in beak shapes and sizes (e.g., insectivorous, vegetarian, cactus-eating, etc.).
-

Australian Marsupials: In the geographically isolated continent of Australia, a vast array of marsupials (such as the kangaroo, koala, bandicoot, and Tasmanian wolf) evolved from a single ancestral marsupial stock. Each adapted to a specific ecological niche within the continent.

• This pattern, where different species evolve from a common ancestor and radiate outward into diverse habitats, is the classic definition of adaptive radiation.

• Let us evaluate the other options:
- They are not all extinct (kangaroos, koalas, and finches are still alive).
- While they have analogous adaptations (due to convergent evolution), they do not share homologous organs across the two distinct groups.
- Only Darwin's finches originated from South America; Australian marsupials evolved in Australia.



Step 4: Final Answer:
The common feature is that both show adaptive radiation, which is option (B).