Beds feel distinctly modern. Probably because every bed nowadays unfurls from a compact cube like a rehydrated food from a sci-fi movie. Or comes packed with futuristic tech that makes the sack your great, great, great grandparents slept on look like a sack stuffed with hay. But beds go back hundreds of thousands of years. And a team of researchers just published evidence of some of the remains from a famous cave that countless human ancestors c…