The use and disuse of body parts and the inheritance of acquired traits were used to explain

Step 1: Analyze the question The question asks which theory is based on two ideas: (1) the use and disuse of body parts, and (2) the inheritance of acquired traits.

Step 2: Explain the concept Jean-Baptiste Lamarck, a French biologist, proposed an early theory of evolution with two main principles:

• Use and disuse: Organs that are used often become bigger and stronger, while organs that are not used become weak and may disappear.
• Inheritance of acquired characteristics: Traits an organism acquires during its lifetime are passed on to its offspring.

The classic example is the giraffe. Lamarck said giraffes stretched their necks to reach high leaves, and their offspring were then born with longer necks.

Step 3: Check each option

• A. Darwin's theory: Darwin's theory is based on natural selection. Individuals with favourable variations survive and reproduce, passing those traits on. It does not rely on use and disuse as its main mechanism.
• B. Lamarck's theory: This matches both ideas exactly.
• C. Genetic drift: This is a random change in allele frequencies in a population, especially a small one. It has nothing to do with use and disuse.
• D. Gene flow: This is the movement of genes between populations through migration. It is also unrelated.

Step 4: Answer The correct answer is B. Lamarck's theory.

Exam tip: Remember "Lamarck = Lambs stretching", or simply: Lamarck = Use and Disuse + Acquired traits inherited. Darwin = Natural Selection and Survival of the fittest. Whenever you see "acquired characters are inherited", think Lamarck straight away.