Question20 Darwin's argument for natural selection required:Select one alternative: Variation in a population; no differences in reproductive fitness between variants; random mating. Heritable variation in a population; humans artificially deciding which variants were fit to breed; over-reproduction of offspring. Inheritance of acquired characters; an organism that developed a trait through effort and exercise could pass that on to offspring; struggle for existence. Heritable variation in a population; differences in reproductive fitness between variants; over-reproduction of offspring. ResetMaximum marks: 1 Flag question undefined

Question

BlackTom AI · Accepted Answer

Heritable variation in a population; differences in reproductive fitness between variants; over-reproduction of offspring.

Heritable variation: For natural selection to produce evolutionary change, individuals must differ in traits and those trait differences must be passed from parents to offspring. If variation is not heritable, any advantage an individual has will not be transmitted and cannot accumulate across generations.

Differences in reproductive fitness: Natural selection acts on differential success at surviving and reproducing. If all variants have equal reproductive success, there is no systematic increase of advantageous traits. Fitness differences mean some variants leave more offspring than others, so their traits become more common.

Over‑reproduction of offspring (struggle for existence): Many more offspring are produced than can survive to reproduce. This creates competition for limited resources, so only some individuals (typically those with advantageous heritable traits) survive and reproduce. Over‑production is the pressure that makes differences in fitness matter.

Step‑by‑step reasoning:
1. Observe variation among individuals in a population.
2. Require that variation be heritable so offspring resemble parents in relevant traits.
3. Because organisms produce more offspring than the environment can support, there is competition.
4. Individuals with heritable traits that confer higher survival/reproductive success leave more offspring.
5. Over generations, those advantageous heritable traits increase in frequency — this is natural selection.

Why the correct option is correct: It explicitly lists the three core requirements Darwin used: heritable variation, differential reproductive success (differences in fitness), and over‑reproduction leading to competition. These are the minimal conditions for natural selection to operate.

Why the other options are incorrect:
- Option 1: “no differences in reproductive fitness” contradicts the need for differential fitness; random mating is irrelevant to the core mechanism.
- Option 2: Emphasizes human artificial selection; Darwin used artificial selection as an analogy but natural selection does not require human choice.
- Option 3: Invokes inheritance of acquired characters (Lamarckism), which is not the mechanism Darwin proposed and cannot by itself produce natural selection.

Therefore the correct answer matches the provided answer: Heritable variation in a population; differences in reproductive fitness between variants; over‑reproduction of offspring.

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