IB Biology HL 4.1.7 Sexual Selection
Practise evaluating HL evidence for sexual selection, including exaggerated traits, mate choice and inherited courtship behaviour.
- Syllabus
- First assessment 2025
- Course
- Biology HL
- Level
- HL
Exam points
- Evaluate mate-choice data to judge whether exaggerated traits influence female preference.
- Explain how inherited courtship behaviour and display traits can evolve through sexual selection.
D4.1.7—Sexual selection question 1
Male eastern bluebirds (Sialia sialis) display brilliant UV-blue feathers on their heads, backs, wings and tails. The brightness index of the male was calculated; the larger the score, the brighter the blue feathers. A brightness value of 0 indicates normal male brightness, so birds with negative scores are less bright than normal.
In an experiment to see the mating behaviour of bluebirds, scientists separated pairs of males and females and then allowed females to choose new partners.
The graph shows the relationship between male brightness index and choice of mate by females in eastern bluebirds.
Question (a)
(a)
Evaluate the hypothesis that females prefer to mate with males whose feathers are a brighter blue.
[ 2 ]
Question (b)
(b)
Explain how natural selection can cause mate selection behaviour patterns to develop in a species such as eastern bluebirds.
[ 3 ]
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