All living organisms are constantly involved in a struggle for existence. This was proposed by

Analyze the question: It asks who proposed that all living organisms are constantly in a "struggle for existence." This is about the theory of evolution and natural selection.

Explain the concept: Charles Darwin's theory of natural selection (in On the Origin of Species, 1859) is built on these ideas:

1. Organisms produce more offspring than can survive.
2. This leads to a struggle for existence, with competition for food, space, mates, and escape from predators and disease.
3. Individuals show variations.
4. Those with favourable variations survive and reproduce ("survival of the fittest").
5. These traits are passed to the next generation.

Check each option:

• A. Morgan: Thomas Hunt Morgan worked on genetics and chromosomes using fruit flies (Drosophila). Not the answer.
• B. Darwin: He made "struggle for existence" a central part of natural selection. Correct.
• C. Lamarck: He proposed the inheritance of acquired characters and the use and disuse of organs. Not the answer.
• D. Wallace: Alfred Russel Wallace independently came up with natural selection and is a plausible distractor. However, the phrase "struggle for existence" is classically credited to Darwin, who developed it in his work, drawing on Malthus's ideas about population.

Answer: The correct option is B. Darwin.

Exam tip: Link names to key ideas:

• Darwin → natural selection, struggle for existence
• Lamarck → use and disuse, acquired characters
• Morgan → chromosomes and genes
• Wallace → co-discoverer of natural selection (but Darwin is usually the JAMB answer)

If you see "struggle for existence" or "survival of the fittest," think Darwin.