In the Early 1900s, a Young Ecologist Shot a Wolf and Watched the Life Leave Its Eyes. That Changed His Position on Conservation
From SmithsonianMag.com:
One day in the early 20th century, in eastern Arizona, a forester—“full of trigger itch,” as he later wrote—leaned over a rimrock ledge, readied his rifle, and shot a wolf. This was hardly unusual: Wolves and other carnivores were mammalia non grata, persecuted for their perceived crimes against livestock and deer.
“In those days, we had never heard of passing up a chance to kill a wolf,” the forester, Aldo Leopold, would recall decades later. More surprising was what followed: remorse.

