Question

DARWIN & NATURAL SELECTION
3. Some adaptations are helpful in one environment, but would be harmful in other
environments. Complete the table below with 5 more adaptations.
4. Explain why sexual reproduction allows a species to evolve more quickly.
5. Explain why a characteristic which helps an animal to live longer will generally tend
to become more common in the population as a result of evolution by natural
selection
Adaptation Helpful Environment Harmful Environment
Thick Fur Cold, arctic environments Hot environments
1. A species of moth has a 2 varieties of wing color: brown and white. As winter approaches, the
trees where the moths live loose their leaves. The moth’s predators are birds who hunt for the
moths as they rest on the dark tree bark. Every moth lays 100 eggs, but only about 10 from each
egg cluster live to adulthood.
Which moth variety do you think will be selected against? ____________________________
Which trait is favorable? Why? _________________________________________________
__________________________________________________________________________
What are the variations in this population? ________________________________________
How does this species overproduce? ____________________________________________
How will this species change over time? _________________________________________
__________________________________________________________________________
2. Only 1 out of 1000 sea turtles survives it to adulthood. From the moment they hatch, sea
turtles must strive for survival. They race across the beach and battle the waves moments after
their birth. Throughout this time, predators are stalking them for an easy meal. Some sea turtles
are faster than others.
Which sea turtle do you think will be selected against? ______________________________
Which trait is favorable? Why? _________________________________________________
__________________________________________________________________________
What are the variations in this population? ________________________________________
How does this species overproduce? ____________________________________________
How will this species change over time

Answer 1

3. Complete the table (5 more adaptations)

Adaptation — Helpful environment — Harmful environment
- Webbed feet — Aquatic/wetland environments — Dry, rocky or mountainous terrain where webbing hinders walking
- Camouflaged coloration (brown/green mottling) — Forests or leaf-littered ground where it matches background — Open/snowy habitats where it stands out
- Long, deep roots — Arid or drought-prone soils (access deep water) — Waterlogged or flooded soils (roots can rot)
- Thick layer of blubber/fat — Cold marine/arctic environments (insulation, energy reserve) — Hot climates (overheating; costly to maintain)
- Large ears (good blood flow) — Hot, arid environments for heat dissipation — Cold climates (increased heat loss)

4. Why sexual reproduction allows a species to evolve more quickly
Sexual reproduction mixes genes from two parents (meiosis and recombination), creating many new combinations of alleles each generation. That increases genetic variation on which natural selection acts, so beneficial allele combinations can appear faster. Recombination also helps separate beneficial mutations from harmful ones, speeding adaptive change and allowing populations to respond more quickly to changing environments.

5. Why a characteristic that helps an animal live longer tends to become more common
If a heritable trait increases an individual’s chance of surviving long enough to reproduce (or to reproduce more often or successfully), individuals with that trait will, on average, leave more offspring carrying the trait. Over generations, natural selection increases the frequency of that trait in the population. (Caveat: the trait must be heritable and not carry large trade-offs that reduce reproductive success.)

1. Moth scenario
- Which moth variety will be selected against? White moths (the lighter-colored variety).
- Which trait is favorable? Why? Brown/dark wing coloration (camouflage). It matches the dark tree bark so birds are less likely to spot and eat the moths, increasing survival to reproduce.
- What are the variations in this population? Variation in wing color (brown vs. white, and shades in between).
- How does this species overproduce? Each moth lays about 100 eggs but only ~10 survive to adulthood — many more offspring are produced than can survive.
- How will this species change over time? The proportion of brown moths will increase and white moths will decrease (directional selection), so the population will become predominantly brown over generations.

2. Sea turtle scenario
- Which sea turtle will be selected against? Slow-moving hatchlings.
- Which trait is favorable? Why? Greater speed/agility at hatching. Faster hatchlings are more likely to outrun predators and reach the sea to survive, so they have higher chances of reaching adulthood and reproducing.
- What are the variations in this population? Variation in hatchling speed, strength, flipper size, body condition at hatching, timing of emergence.
- How does this species overproduce? Females lay many eggs (and many hatchlings emerge), but only about 1 in 1,000 survive to adulthood — far more offspring are produced than survive.
- How will this species change over time? The population will tend to shift toward faster hatchlings (directional selection): average hatchling speed and traits that confer speed will increase in frequency if those traits are heritable.