Question

The graph shows the relationship between a variable on the x-axis and genetic diversity on the y-axis. Each point represents a species and the trend line describes the relationship across species. 

Select the most appropriate variable for the x-axis.

• A. Evolutionary age of species
• B. Abundance
• C. Body size
• D. Geographic range

Hint:

In biology, larger species often have lower genetic diversity due to limited gene flow and smaller populations. This can result in a negative correlation between body size and genetic diversity.

Answer 1

The Correct Option is C

Step 1: Interpreting the graph.
The graph shows a negative relationship between the variable on the x-axis and genetic diversity on the y-axis. As the x-axis variable increases, the genetic diversity decreases. This suggests that the variable on the x-axis is something that increases with size or scope and correlates with a decrease in genetic diversity.

Step 2: Analyzing the options.
- (A) Evolutionary age of species: While older species could potentially show reduced genetic diversity due to longer evolutionary periods, this is not the most likely variable for this trend. Evolutionary age typically doesn't show such a direct and consistent negative correlation with genetic diversity.
- (B) Abundance: Species abundance could be related to genetic diversity, but the graph suggests a direct relationship based on size or physical traits, not abundance.
- (C) Body size: Body size is a known variable that often shows a negative correlation with genetic diversity. Larger species tend to have lower genetic diversity due to their smaller populations and more restricted gene pools. This matches the pattern shown in the graph.
- (D) Geographic range: Although geographic range might influence genetic diversity, the graph suggests a more direct and consistent correlation with size rather than spatial factors.

Step 3: Conclusion.
Thus, the most appropriate variable for the x-axis is body size, which explains the observed negative relationship with genetic diversity.

Final Answer: \boxed{(C)}