Q89. Which one of the following is the smallest biological unit capable of evolving over time?
- A cell
- An individual organism
- A population
- A species
Evolution occurs through changes in allele frequencies across generations, requiring genetic variation within breeding groups. Individuals do not evolve; populations do as natural selection, drift, mutation, and gene flow alter genetic composition over time. This defines microevolution at the population level.
Correct Answer
A population is the smallest biological unit capable of evolving over time.
It consists of interbreeding individuals of the same species in a defined area where heritable traits shift via differential reproduction.
Genetic diversity within populations provides raw material for adaptive changes.Option Analysis
A Cell
Cells replicate and mutate but lack the multicellular complexity for population-level evolution.
Prokaryotic cells evolve via binary fission, yet true Darwinian evolution needs sexual recombination in groups.
Not considered the standard unit in multicellular organism contexts.An Individual Organism
Individuals develop, adapt behaviorally, and acquire traits but cannot evolve genetically across generations.
Their genome is fixed post-zygote; reproduction passes genes to populations.
Lifetime changes (e.g., Lamarckian) do not alter heritable evolution.A Population (Correct)
Allele frequencies change measurably here through selection pressures acting on variation.
Examples: peppered moth populations shifting color during industrialization.
Smallest group tracking microevolutionary shifts.A Species
Species comprise multiple populations; evolution occurs within subpopulations first.
Macroevolution (speciation) builds from population changes, making it larger.
Not the smallest unit.Option Capable of Evolving? Reason Scale of Change A Cell No Lacks group genetics Cellular replication Individual Organism No Fixed genome post-birth Personal adaptation Population Yes Allele frequency shifts Microevolution Species Yes, but larger Multiple populations Macroevolution Populations bridge micro- and macroevolution, fundamental to modern synthesis.
