For years, scientists have debated the who-what-when-where’s of humanity’s expansion into the Americas. Who were the “first Americans”? And was there one founding wave of migration, or several? This week, two studies published in Science
seek to answer some of those questions using DNA evidence from modern and ancient human genomes. Their results introduce yet another mystery into the tale of the peopling of the Americas: How did indigenous peoples in the Amazon end up with DNA traces similar to those of indigenous Australians and New Guineans?