Natural Selection

Read the explanation of adaptations and the polar bear example.

Students consider what they know about lions, koala bears, and humans to consider why an adaptation is important. Some possible answers may include:

• A lion’s sharp claws can help grip the ground when running, or trees when climbing. Their claws are also useful weapons for killing prey, and useful tools for ripping through the coats of their prey to get to the meat.
• Koalas spend most of their time in trees, where they can eat leaves and avoid predators on the ground. Their paws are adapted for keeping a firm, safe grip on branches so they can climb well and not fall. The thick pad on their tail makes it easier to sit in trees all day.
• Humans need to be able to keep their body temperature in a healthy range. If they are in a very hot place, or heat up because they are doing hard physical work, cooling off by sweating helps them avoid reaching dangerously high temperatures.

Other adaptations include:

• The camel’s hump, which stores fat (not water!) that they can metabolize for energy when food is scarce. This efficient metabolism allows them to go months without drinking water.
• The hedgehog’s spines, which protect them from predators.
• An alligator’s eyes, ears, and nose: they are positioned to peek just above the waterline so they can locate their prey without being seen.

This activity asks students to elaborate on how they think an adaptation evolved. Answers will vary; encourage students to speculate but to be logical in their explanations.

Examine the illustrations on the worksheet together, then allow partners to discuss and write their responses.

Possible explanations:

Perhaps the katydid’s ancestors looked like regular grasshoppers or something. However, in a process similar to the peppered moth case, there might have been some that looked more like leaves. These better-camouflaged ones would have been harder for predators to notice. As a result, the insects with leaf-like features survived in greater numbers to breed. As time went on, these traits were passed down and created what we now call the katydid.

The woodpecker’s food source is bugs that live beneath the bark of trees. Maybe the woodpecker evolved from a bird that ate bugs that were more accessible. Those birds that were slightly better at picking away bark to find hidden insects would have had an advantage. Over many generations, some of the birds might have gradually become more specialized at hunting insects in wood. These specialists would have access to a food source that other birds couldn’t compete for. But the specialists would also need to maintain their abilities: woodpeckers born without the right kind of beak or skull would tend to die (from starvation or injury) before breeding, taking their traits out of the population. Traits that favored hunting insects inside of wood would be the ones passed on to woodpecker offspring.

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