Darwins Natural Selection worksheet - Free Printable

Let's solve each question step by step, using Darwin’s four points of natural selection:

Darwin’s Four Points of Natural Selection:

1. Variation: Individuals in a population have differences (traits).
2. Overproduction: Organisms produce more offspring than can survive.
3. Struggle for existence: Limited resources lead to competition.
4. Survival of the fittest / Descent with modification: Individuals with beneficial traits are more likely to survive and reproduce, passing on those traits.

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## Problem 1: Worms – Nocturnal vs. Diurnal

> There are two types of worms: nocturnal (eat at night) and diurnal (eat during the day). Birds eat during the day and seem to eat ONLY the diurnal worms. The nocturnal worms are in their burrows during this time. Each spring when the worms reproduce, they have about 500 babies but only 100 of these 500 ever become old enough to reproduce.

a. Which worm has natural selection selected AGAINST? FOR?

- Selected AGAINST: Diurnal worms
(Because birds eat them during the day, reducing their survival.)

- Selected FOR: Nocturnal worms
(They avoid predation by being active at night, so they are more likely to survive and reproduce.)

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b. Identify Darwin’s 4 points in the scenario above.

#### i. How does the population have variation?
There is variation in feeding behavior: some worms are active during the day (diurnal), others at night (nocturnal).

#### ii. Which variation is an adaptation (beneficial)?
The nocturnal behavior is an adaptation because it helps worms avoid bird predators during the day.

#### iii. How is the population overproducing?
Each worm produces about 500 babies, but only 100 survive to reproductive age — meaning there is overproduction of offspring.

#### iv. Which population will descend with modification?
The nocturnal worms will pass on their traits to the next generation. Over time, the population will have more nocturnal individuals — this is descent with modification.

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## Problem 2: Polar Bears – Thick, Thin, and Medium Coats

> There are three types of polar bears: thick coats, thin coats, and medium coats. It's fall, temperatures dropping quickly. Bears must stay warm or freeze to death. Many mothers had 2 cubs, but due to extreme cold, many now have only one cub left.

a. Which bear will natural selection select AGAINST? FOR?

- Selected AGAINST: Bears with thin coats
(They cannot retain heat well and are more likely to die in cold weather.)

- Selected FOR: Bears with thick coats
(They are better insulated and more likely to survive the harsh winter.)

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b. Identify Darwin’s 4 points in the scenario above.

#### i. How does the population have variation?
There is variation in coat thickness: some bears have thick coats, some thin, and some medium.

#### ii. Which variation is an adaptation (beneficial)?
Thick coat is the beneficial adaptation because it provides better insulation in cold environments.

#### iii. How is the population overproducing?
Many mothers have 2 cubs, but due to harsh conditions, only one survives — indicating that more offspring are produced than can survive.

#### iv. Which population will descend with modification?
The bears with thick coats will survive and reproduce more successfully. Their offspring will inherit thick coats, leading to a population that gradually becomes better adapted to cold — this is descent with modification.

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✔ Final Summary:

| Question | Answer |
|--------|--------|
| 1a | Against: Diurnal worms; For: Nocturnal worms |
| 1b i | Variation in feeding time (diurnal vs. nocturnal) |
| 1b ii | Nocturnal behavior (avoids predation) |
| 1b iii | 500 babies born, only 100 survive |
| 1b iv | Nocturnal worms |
| 2a | Against: Thin-coated bears; For: Thick-coated bears |
| 2b i | Variation in coat thickness |
| 2b ii | Thick coat (better insulation) |
| 2b iii | 2 cubs per mother, but only 1 often survives |
| 2b iv | Thick-coated bears |

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This worksheet demonstrates how natural selection acts on existing variation in populations, favoring traits that enhance survival and reproduction in a given environment.