looking at three lines of graffiti written in pencil on the white limestone wall of Mammoth Cave. “A Rust 1861, W Garnett, V Hobartt 5th A G 1861,” read the faint cursive. Today, such casual vandalism ...

and a change to the gene MC1R gave the mice a mammoth’s trademark rusty color. To avoid any concerns about mouse health, researchers used gene variants which have been observed in healthy mice ...