Sexual Selection

Question 1

Scientists studying a species of jungle birds called "crimson‑throated tanagers" find that males have ever larger, brighter throat patches. The patches make it harder for the birds to escape predators, yet female tanagers always choose mates with the biggest patches. Which statement best explains why this pattern is an example of runaway sexual selection?

Accepted Answer

Females prefer larger throat patches, so males with bigger patches have more offspring; the genes for the big patch and the preference for it become linked and increase together, causing the patches to become exaggerated even though they reduce survival.

Answer

Predators avoid birds with bright throat patches, so the patches spread because they provide safety from being eaten.

Answer

The big throat patches arise by chance and persist because they do not affect the birds' chances of reproducing.

Answer

The large throat patches help males locate food more efficiently, so males with bigger patches survive better and thus reproduce more.

Question 2

Which statement most accurately explains why peacocks have such bright, large tails?

Accepted Answer

Female peacocks prefer males with larger, brighter tails, so those males have more offspring and the trait becomes more exaggerated even though it can be costly.

Answer

Peacock tails are large because the gene for tail size spreads randomly in the population, regardless of any advantage.

Answer

Peacocks use their tails to run faster away from predators, so natural selection favored longer tails for speed.

Answer

The bright tail scares away predators, so peacocks with bigger tails survive longer.

Question 3

Which explanation most accurately describes the self‑reinforcing evolutionary process that can produce an extremely long, bright tail in male peacocks?

Accepted Answer

Females prefer males with longer, brighter tails; those males sire more offspring, so the preference and the trait strengthen each other over generations, making the tail larger even though it may reduce survival.

Answer

The bright tail evolved because it better regulates the bird’s body temperature, giving individuals with larger tails a physiological advantage.

Answer

Males with longer tails can store more food in the feathers, allowing them to survive winter better, so longer tails are selected for increased stamina.

Answer

A longer tail helps peacocks run faster away from predators, so natural selection directly favors longer tails for survival.

Try three questions

Which statement most accurately explains why peacocks have such bright, large tails?

Which explanation most accurately describes the self‑reinforcing evolutionary process that can produce an extremely long, bright tail in male peacocks?

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