The flippers of a whale and the fins of a fish are examples of?

Analyze the question: It asks what kind of evolutionary relationship exists between a whale's flippers and a fish's fins. The two structures look alike and do the same job (swimming), but whales and fish are very distantly related.

Concept:

• Convergent evolution: unrelated organisms evolve similar features because they adapt to similar environments or ways of life. The structures are analogous, meaning they have the same function but different evolutionary origins.
• Divergent evolution: related organisms with a common ancestor develop different structures. These are homologous structures, such as the human arm, bat wing and whale flipper.
• Coevolution: two species evolve in response to each other, as with flowers and their pollinators.
• Continuous variation: a range of traits within a population with no distinct categories, such as height or weight.

Solution:

1. A whale is a mammal and a fish is a fish. Their last common ancestor lived very long ago.
2. Both live in water and swim, so natural selection favoured a streamlined body with paddle-like limbs in each.
3. The structures are similar in function and appearance but have different origins. A whale's flipper contains the bones of a mammalian limb, while a fish's fin is supported by fin rays. These are analogous structures.
4. Analogous structures are evidence of convergent evolution.

Answer: D. convergent evolution

Tip: Remember "Convergent = Come from different ancestors but look the same (analogous)." Divergent evolution is the reverse: the same ancestor, different forms (homologous). For example, the whale flipper and the bat wing are divergent, but the whale flipper and the fish fin are convergent.