Nobody doesn’t like Mark Twain, aka Samuel Clemens, but there were lots of people Twain didn’t like, e.g., cockfighters, hunters, and vivisectionists. He was a social revolutionary and one of the pioneer proponents of animal advocacy in an era when kids, women, blacks, dogs and horses were routinely abused and destroying wildlife was the American way. He was also an ardent Darwinian, one of the first public figures to embrace evolution.