The first systematic study was not conducted until the 1920s, when Carl Akeley of the American Museum of Natural History traveled to Africa to hunt for an animal to be shot and stuffed. On his first trip, he was accompanied by his friends Mary Bradley, a mystery writer, her husband, and their young daughter Alice, who would later write science fiction under the pseudonym James Tiptree Jr. After their trip, Mary Bradley wrote "On the Gorilla Trail". She later became an advocate for the conservation of gorillas, and wrote several more books (mainly for children). In the late 1920s and early 1930s, Robert Yerkes and his wife Ava helped further the study of gorillas when they sent Harold Bigham to Africa. Yerkes also wrote a book in 1929 about the great apes.