Researchers have found that endurance running ability may signal reproductive potential in males that signal sexual attraction in females. In the study, finger length ratio (known as the 2D 4D ratio) was used as a marker for performance on the track. It so happens that the marathon runners who had a low digit ratio showed better scores 
than those with high ratios. A low 2D 4D ratio correlated with exposure to higher levels of testosterone in the womb. Signaling theories of male resourcefulness in hunter-gatherer times, with attributes such as intelligence and athleticism. Good long distance runners are essentially better hunters. So depending on how efficiently one can run long distances would be an inherent biological reproductive marker for the female species.