TEMPE, AZ—Providing a definitive explanation as to how and why early humans evolved away from their closest primate relatives, researchers at the Arizona State University Institute of Human Origins presented findings Tuesday confirming that our species’ first ancestors began to climb down from trees to retrieve snacks they had dropped.Anatomical evidence from the 6-million-year-old fossilized remains of Sahelanthropus peinaó—which was unearthed earlier this year in South Africa and is now believed to be the last common ancestor shared by chimpanzees and modern humans—suggests that the animal frequently descended from the jungle canopy to retrieve delicious morsels that it fumbled from its pudgy hands due to inattention, overeager eating, or a loosening grasp as it dozed off after a meal.