why should we expect a data collection of grasshopper femur span to result in a double bell curve on a graph?

Question

Ithe actual question is from a bio lab practical ws i have to do. The actual question is: Most years, data collection of grasshopper femurs and human hand span results in a double bell curve. Why should we expect this to happen. If possible give an answere for both grasshopper and hand. thank you

Answer 1

Male and females have a different average femur/hand span, resulting in two bell curves? Or is this too obvious an answer?

Answer 2

Because males and females are not the same average size.