Which of the following supports using sticklebacks as a model organism?

• A. Abundant fossils enabling comparisons to ancestors
• B. They only live in freshwater
• C. They lack genetic variation
• D. They have no fossil record

Answer: (A)

Having abundant fossils lets scientists connect modern biology to long-term history, letting them track how traits and lineages change and calibrate evolutionary timelines. For sticklebacks, this means you can compare today’s populations to ancient forms, study how they repeatedly adapted when moving between marine and freshwater environments, and tie together paleontological data with genetics. That combination — historical context, natural variation, and a well-understood genome — makes sticklebacks especially suitable as a model organism. The other statements don’t fit because they misstate sticklebacks’ biology: they don’t live only in freshwater, they do show genetic variation, and there is a fossil record.