Origins of Life, Natural Selection & Evolution | wilcoxbiology - Free Printable

Here is a clear, step-by-step solution to the 4 questions based on the image provided. Since you are instructed to answer in your notebook, I’ll write this as if you’re copying it into your notebook — complete with explanations.

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Page 83

1. Describe what is happening in figures 1–3.

In Figure 1, we see a population of mice living on tan sand. Some mice are light-colored (cream or tan), and some are dark-colored (black or black-and-tan). In Figure 2, a hawk (a predator) is shown swooping down to catch a mouse — specifically, a dark-colored one that stands out against the tan sand. In Figure 3, after the hawk has hunted, there are fewer dark-colored mice and more light-colored mice remaining. This shows how predators selectively remove individuals that are easier to see, leaving behind those better camouflaged in their environment.

> *This illustrates natural selection: the environment (predation + background color) favors certain traits over others.*

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2. Is the population of mice different in figure 3 than in figure 1? Explain why.

Yes, the population of mice is different in Figure 3 compared to Figure 1.

In Figure 1, there is a mix of light and dark mice. In Figure 3, the dark mice have been mostly eliminated by the hawk because they are more visible against the tan sand. The surviving mice are mostly light-colored (tan or cream), which blend in better with the environment.

This change happened because the dark mice were less adapted to their environment — they were easier for the hawk to spot and catch. The light-colored mice had a survival advantage (camouflage), so they lived longer and were more likely to reproduce. Over time, this leads to a population shift toward the better-adapted trait.

> *Natural selection caused a change in the population’s traits — not because the mice changed color, but because the ones with advantageous traits survived and passed them on.*

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3. For the mice in the figure, what characteristic was an adaptation that increased fitness?

The adaptation that increased fitness was fur color matching the tan sand (specifically, tan or cream fur).

Fitness, as defined here, is “the ability to survive and reproduce.” Mice with fur that matched the tan sand were harder for hawks to see, so they were more likely to survive predation. Surviving longer gave them more chances to reproduce and pass on their genes. Therefore, camouflage through fur color directly increased their fitness.

> *Adaptations are inherited traits that improve survival/reproduction — in this case, fur color that provides camouflage is the key adaptation.*

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4. According to the definition given above for fitness, which mouse would biologists consider the fittest? Explain why this mouse would be the fittest.

According to the definition — “fitness is the ability to survive and reproduce” — the Tan mouse would be considered the fittest.

Here’s why:

- Survival: The Tan mouse lives for 8 months — much longer than the Black (2 months), Tan-and-Black (4 months), and Cream (4 months) mice.
- Reproduction: The Tan mouse produces 11 pups — more than any other mouse (Tan-and-Black: 5; Cream: 4; Black: 0).
- Combination of both: Fitness requires both surviving long enough to reproduce AND producing offspring. The Tan mouse excels at both.

Even though the Black mouse runs faster (8 cm/sec vs. Tan’s 6 cm/sec), speed doesn’t help if the mouse is easily seen and caught early. The Tan mouse’s camouflage allows it to survive longer and reproduce more — making it the most fit according to evolutionary biology.

> *Biologists measure fitness by reproductive success over a lifetime — not just speed or strength. The Tan mouse passes on the most genes to the next generation.*

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✔ Summary for Notebook:

You’ve now explained:
- How predation changes mouse populations (Q1 & Q2),
- Why camouflage is an adaptation (Q3),
- And how to calculate fitness using survival + reproduction (Q4).

This is a classic example of natural selection — where heritable traits that improve survival and reproduction become more common in a population over time.

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Let me know if you want to turn this into a diagram or add drawings to your notebook!