The graphs show the beak length of offspring of a wild bird population in 2000 and in 2020. The graphs are drawn to the same scale.
Which change has taken place in the overall beak length of the bird population, and what type of selection has brought this about? 
▶️ Answer/Explanation
Ans: D
The graph shows a shift toward longer beak lengths in 2020 compared to 2000, indicating directional selection. This occurs when one extreme phenotype (longer beaks) is favored over others due to environmental pressures (e.g., changes in food availability).
Stabilizing selection (A, B) reduces variation around the mean, while disruptive selection (C) favors both extremes. Since the population shifted toward longer beaks, D (increased, directional) is correct.
The photograph shows a species of fish called a leafy sea-dragon.
Leafy sea-dragons live in areas of the sea where seaweed is present.
Which statements explain how natural selection caused the leafy sea-dragon species to develop?
1. Leafy sea-dragons that looked like seaweed were better adapted to their environment.
2. Leafy sea-dragons that survived passed on the allele for their appearance to their offspring.
3. Humans selected leafy sea-dragons that looked like seaweed.
A) 1,2 and 3
B) 1 and 2 only
C) 1 and 3 only
D) 2 and 3 only
▶️ Answer/Explanation
Ans: B) 1 and 2 only
The leafy sea-dragon’s seaweed-like appearance evolved through natural selection:
- Camouflage advantage: Individuals resembling seaweed avoided predators better (statement 1).
- Inheritance of traits: Survivors passed these advantageous alleles to offspring (statement 2).
Statement 3 is incorrect because human selection didn’t drive this adaptation – it occurred naturally over generations through differential survival and reproduction.