IB ESS SL 3.1.5 Natural Selection Process Question Bank
Trace variation, selection pressure, differential reproduction and inheritance in a natural-selection example.
- Syllabus
- First assessment 2026
- Course
- ESS SL
- Level
- SL
Trace variation, selection pressure, differential reproduction and inheritance in a natural-selection example.

Figure:Fact file on Mindo cloud forest

Figure:Fact file on Mindo harlequin toad
red and falls off.
There is no cure and those infected experience 85−100% mortality.
Explain how the disease in the Mindo harlequin toad could contribute to the evolution of resistance to this disease in the species for future generations.
a. Natural selection/survival of the fittest;
b. Random (genetic) mutations/variations in each generation would eventually produce some individuals with a (genetic) resistance to the fungus / The disease acts as a selection pressure, meaning only individuals with advantageous alleles survive;
c. Those that survive would produce offspring inheriting that same resistance;
d. Over many generations, the frequency of the resistance allele/gene increases in the population;
e. This leads to a population better suited to survive in environments where the fungus is present;
Note to examiners: do not accept responses which state that organisms adapt to the disease.