Danielle Tepper had always loved dolphins. When she went on vacation to Hawai'i, she knew she had to see them firsthand. Tepper—now a senior editor at the Humane Society of the United States—wanted to do it ethically, so she avoided captive dolphin attractions. Instead, she booked an excursion to...

Somewhere toward the end of the last ice age, we formed an alliance with wolves: Maybe the ancestors of dogs got food scraps while our own ancestors gained protection from predators and other humans. These social species eventually collaborated on a vast scale, possibly even hunting woolly mammoths...