Question

one student created the diagram below to represent their understanding of how this population of fish evolved over time. there is genetic variation in the hudson river tomcod. some fish are naturally resistant to pcbs. fish that were resistant to pcbs survived better than others. over time, there we more fish who wer resistant to pcbs. which two additional statements would most strengthen the students explanation of how the tomcod have evolved through natural selection? tomcod populations have steadily declined throughout their habitats in the last ten years. tomcod are eaten by multiple predators, including striped bass and several waterbirds. the fish who were resistant to pcbs are more likely to pass their genes to offspring. this particular population of tomcod fish only spawns in the lower hudson estuary. the release of pcb into the river greatly increased the levels of pcb in the river.

Explanation:

• Natural selection involves traits that enhance survival and reproduction being passed on. If fish resistant to PCBs pass their genes (statement 3), it supports evolution via natural selection.
• An increase in PCB levels (statement 5) provides the selective pressure (environmental factor) that would favor PCB - resistant fish, strengthening the natural - selection explanation.

Answer:

The two statements that most strengthen the student’s explanation are “The fish who were resistant to PCBs are more likely to pass their genes to offspring” and “The release of PCB into the river greatly increased the levels of PCB in the river”.