Mary Whitney named her dog Biko after South African civil rights activist Stephen Biko.   David Briggs

Like many young girls enamored with animals, Mary Whitney wanted to become a veterinarian. Unlike most girls, she experienced, as she says, “the true calling.” Without that, she firmly believes no one should ever enter the demanding profession. “It has to be the only thing you can ever imagine yourself doing,” she says.

Mary grew up in . . .