“Natural selection is often said to be a tinkerer, not an engineer…. Traits that evolve by natural selection do not come from scratch,” Fessler said.

To test this theory, researchers set up a series of experiments in which they had hundreds of participants look at photos of hands holding different objects: handguns, handsaws, power drills and caulking guns. (The hands matched one another in size and appearance.)

Participants were asked to look at the photos and estimate the size of the person holding each object and how muscular he was by choosing one of six body types.

In one round of the experiment involving 628 viewers, the researchers found that men whose hands held a .357-caliber handgun were thought to be almost 5 feet, 10 inches — more than 2 inches taller than men whose hands held a caulking gun.