4. How does an adaptation, such as better running speed, evolve with natural selection?
a.
Natural selection directionally produces better adaptation over time, gradually leading
to better running speed.
b.
Natural selection makes individuals with favourable traits such as better running
speed more attractive, ensuring they produce more offspring
c.
Natural selection involves random mutations, some of which are beneficial
adaptations. Heritable beneficial adaptations lead to offspring with higher survival.
d.
Natural selection produces individuals with favourable traits, such as better running
speed, who survive better. Individuals with unfavourable traits do not survive, ensuring that all
individuals in future populations have better running speeds.

The correct answer is c. Natural selection involves random mutations, some of which are beneficial adaptations. Heritable beneficial adaptations lead to offspring with higher survival. Natural selection acts on existing genetic variation from random mutations, favoring heritable traits like faster running speed that improve survival and reproduction, gradually changing population allele frequencies over generations.

Natural Selection Mechanism

Natural selection requires three prerequisites: variation, heritability, and differential survival/reproduction. Random mutations create genetic variation; beneficial mutations (e.g., muscle fiber variants for speed) increase fitness when inherited. Individuals with advantageous traits produce more offspring, shifting population traits directionally.

Option Analysis

• a. Natural selection directionally produces better adaptation over time, gradually leading to better running speed: Incorrect; natural selection doesn’t create mutations—it selects existing ones. Lamarckian idea of directed production is wrong.

• b. Natural selection makes individuals with favourable traits such as better running speed more attractive, ensuring they produce more offspring: Incorrect; confuses natural with sexual selection. Fitness means reproductive success, not just mating attractiveness.

• c. Natural selection involves random mutations, some of which are beneficial adaptations. Heritable beneficial adaptations lead to offspring with higher survival: Correct; captures modern synthesis—mutation provides variation, selection filters for fitness.

• d. Natural selection produces individuals with favourable traits, such as better running speed, who survive better. Individuals with unfavourable traits do not survive, ensuring that all individuals in future populations have better running speeds: Incorrect; implies 100% elimination of unfavorable traits (blending inheritance fallacy) and that selection “produces” traits.

CSIR NET Exam Relevance

This tests Darwin vs. modern synthesis understanding. Key formula: change in allele frequency Δp = (pqs)/ (1 – pqs²), where s = selection coefficient. Examples: peppered moth, antibiotic resistance. Aspirants: distinguish mechanism from outcome.