Earth's Children is a series of epic historical fiction (or more precisely, prehistorical fiction) novels written by Jean M. Auel set circa 30,000 years before the present day. There are six novels in the series. Although Auel had previously mentioned in interviews that there would be a seventh novel, publicity announcements for the sixth confirmed it would be the final book in the sequence. The series is set in Europe during the Upper Paleolithic era, after the date of the first ceramics discovered, but before the last advance of glaciers. The books focus on the period of co-existence between Cro-Magnons and Neanderthals. As a whole, the series is a tale of personal discovery: coming-of-age, invention, cultural complexities, and, beginning with the second book, explicit romantic sex. It tells the story of Ayla, an orphaned Cro-Magnon girl who is adopted and raised by a tribe of Neanderthals and who later embarks on a journey to find the Others (her own kind), meeting along the way her romantic interest and supporting co-protagonist, Jondalar. The story arc in part comprises a travel tale, in which the two lovers journey from the region of Ukraine to Jondalar's home in what is now France, along an indirect route up the Danube River valley. In the third and fourth works, they meet various groups of Cro-Magnons and encounter their culture and technology. The couple finally return to southwestern France and Jondalar's people in the fifth novel. The series includes a highly detailed focus on botany, herbology, herbal medicine, archaeology and anthropology, but it also features substantial amounts of romance, coming-of-age crises, and—employing significant literary license—the attribution of certain advances and inventions to the protagonists. In addition, Auel's series incorporates a number of recent archeological and anthropological theories. It also suggested the notion of Sapiens-Neanderthal interbreeding. The author's treatment of unconventional sexual practices (which are central to her hypothesized nature-centered religions) and frequent explicit depictions of sex has earned the series a top twenty place on the American Library Association's list of the 100 Most Frequently Challenged Books of 1990–1999. The books The Clan of the Cave Bear The first book, The Clan of the Cave Bear was released in September 1980 and is a story of personal development set in pre-historic southern Europe during the current Ice Age but before the last glacial period. It introduces the reader to a wide variety of diverse topics, including