Despite the relatively recent age of the early shoes found to date, scientists believe that humans were wearing shoes as much as 40,000 years ago. Shoes made of reeds, papyrus, or even leather decompose easily, leaving few or no traces. But people who don’t wear shoes have wider feet and bigger gaps between their big toe and the other four. In studying bones of the smaller toes of fossilized skeletons, scientists observed that the thickness of these bones decreased somewhere between 40,000 and 26,000 years ago. They believe the change was the result of wearing shoes.
In studying bones of the smaller toes of fossilized skeletons, scientists observed that the thickness of these bones decreased somewhere between 40,000 and 26,000 years ago.

How does the sentence develop the author’s claim in the passage?

A.
It shows how the scientists made their conclusions about what materials were used to make shoes.
B.
It explains why people used reeds and papyrus to make their shoes.
C.
It explains why the thickness of bones decreased in fossilized skeletons.
D.
It shows how the scientists made their conclusions about when people began wearing shoes.