Question

Which one or more of the following is/are NOT essential for evolution by natural selection to take place in a population?

• A. There must be variation in the trait
• B. The trait must be linked with differential reproductive success
• C. The trait must be either fully or partially heritable
• D. The population must comprise of sexually reproducing organisms

Hint:

Recall the three basic requirements for natural selection: variation, heritability, and a link to reproductive success. Check if sexual reproduction is one of these three.

Answer 1

The Correct Option is D

Step 1: Understanding the Question.
The question asks which of the four listed conditions is not one of the basic requirements for natural selection to act on a population. To answer this, we need to recall what natural selection actually needs to work, and then check each option against that list.

Step 2: Key Concept.
Natural selection needs exactly three ingredients in a population, no more and no fewer. First, there must be variation in a trait among individuals. Second, that variation must be linked to differences in survival or reproductive success (some variants leave more offspring than others). Third, the trait must be heritable, at least in part, so that offspring resemble their parents for that trait. If all three hold, the trait that gives higher reproductive success will become more common over generations.

Step 3: Detailed Explanation.
Option (A) says there must be variation in the trait. This is required, since selection needs something to act on; without variation every individual is identical and there is nothing to favour.
Option (B) says the trait must be linked with differential reproductive success. This is required too, since selection works only if some trait values lead to more surviving offspring than others.
Option (C) says the trait must be either fully or partially heritable. This is also required, because if offspring do not inherit the trait from parents, the population composition cannot shift across generations even if some individuals reproduce more.
Option (D) says the population must comprise of sexually reproducing organisms. This is not a requirement. Natural selection also acts in purely asexual populations, such as bacteria that reproduce by binary fission, or in clonal lineages. As long as variation, heritability and differential reproductive success are present, sexual reproduction is not needed at all.

Step 4: Final Answer.
Options (A), (B) and (C) list the three genuine requirements of natural selection, so the one that is NOT essential is (D).
\[ \boxed{\text{(D) Sexually reproducing organisms are not required}} \]