California’s highway State Route 54, skirting southeast of San Diego, doesn’t seem like it would be the catalyst for challenging some of the longest-held ideas about human evolution and our spread across the planet. And yet, in 1992, along SR 54’s ribbons of asphalt and exit ramps to malls, taco joints, and subdivisions, road-widening construction unearthed a fossil that could rewrite the human story—if scientists ever stop arguing about it. Here, 130,000 years ago beside the future site of SR 54, a young mastodon perished. There’s nothing uncommon about that—these…
