New genetic research is reshaping how scientists understand ancient relationships between early humans and Neanderthals. A study published in Science suggests that mating between Homo sapiens women and Neanderthal men occurred more often than the reverse, leaving a lasting mark on the human genome. The finding helps explain a long-standing mystery in genetics. Modern humans carry small amounts of Neanderthal DNA across most of their genome, but almost none on the X chromosome. These gaps, known as Neanderthal deserts, puzzled scientists for years. Modern humans and Neanderthals split from a shared ancestor about 600,000 years ago. Human ancestors evolved in...