Genetic hints of extinct human lineages — and the benefits we might have received from having sex with them — were among the discoveries this year regarding the evolution of our species.

Other key findings include evidence strengthening the case that fossils in South Africa might be those of the ancestor of the human lineage. Research also suggests humans crossed what is now the desolate Arabian Desert to expand out of Africa across the world.

Sex with extinct human lineages

Although we modern humans are the only surviving members of our lineage, other kinds of humans once roamed the Earth, including familiar Neanderthals and the newfound Denisovans, who lived in what is now Siberia. Although some researchers once scoffed at the notion that our ancestors interbred with such extinct lineages, genetic analysis suggests that Neanderthal DNA makes up 1 percent to 4 percent of modern Eurasian genomes, while Denisovan DNA makes up 4 percent to 6 percent of modern Melanesian genomes....