Why is the stickleback a model organism for studying evolution?

• A. They show repeated recent evolution in postglacial lakes
• B. They show ancient fixed traits
• C. They have no genetic variation
• D. Their evolution cannot be traced in fossils

Answer: (A)

This question is about showing evolution in action through repeated natural experiments. Sticklebacks are powerful model organisms because they undergo rapid, repeated evolutionary changes after shifting from marine to freshwater environments in postglacial lakes. In many independent lake populations, they converge on similar traits—like reduced armor plating and changes in pelvic structures—despite being geographically separate. This parallel evolution provides a clean, natural setup to compare how selection acts and how genetic variation is used to produce adaptive traits, all within short timescales that we can study directly. The repeated, predictable patterns across many populations make them ideal for uncovering how evolution proceeds in response to ecological change.

Regarding the other statements: sticklebacks do have genetic variation and do not rely on ancient fixed traits; their ongoing adaptation is well documented. Fossil records exist for the lineage, but the strongest evidence for their use as a model comes from contemporary populations and genetic data showing repeated, parallel evolution.