Earlier this year, while flying over northern Botswana, Vanessa Hayes looked out over the Makgadikgadi Pans—giant salt flats that stretch for more than 6,000 square miles. They are the remnants of what was once Africa’s largest lake. Hayes could see traces of the lake’s shoreline from the air. She glimpsed massive fault lines running across its former bed—signs of the tectonic activity that eventually broke it apart into a patchwork of lush wetlands. For Hayes, who is a geneticist at the Garvan Institute of Medical Research, the view carried a special significance. She thinks that this region was once humanity’s homeland—the place where the ancestors of modern humans got their start.
Hayes and her team analyzed the DNA of 1,217 people from southern Africa who represent a particularly important and poorly studied slice of human genetic diversity. By using that DNA to create a family tree, the team calculated that anatomically modern humans originated in the Makgadikgadi wetlands about 200,000 years ago. They then stayed put for about 70,000 years, before climatic changes allowed some of them to venture outward to other parts of Africa, and eventually to other continents.
But her claims are proving controversial, and other researchers I contacted were either skeptical or outright mad. The study, they noted, is based on just a sliver of DNA from living people, and doesn’t account for the rest of the genome, DNA from ancient human specimens, fossils, or stone tools and other cultural artifacts—all of which suggest that humans arose much earlier, and in a variety of locations. “It ignores a swath of evidence supporting an older origin for our species,” said Eleanor Scerri, an archaeologist who studies human origins at the Max Planck Institute for the Science of Human History.