alt Hacker NewsWell, evaluating the nature of this thought experiment reveals what you actually believe about human evolution and development. I find it extremely hard to believe that someone from 40k years ago would be indistinguishable from humans today. Believing this requires you to imagine that there are no genetic selection pressures for things like intelligence, behavior, physical ability ... 40k years ago had Earth as an almost entirely different planet. Europe was frozen for most of the year, for example. There were no trees. Very, very hard to believe that people born back then could grow up to sit in front of a laptop today.
All we know basically is that their skeletons are undistinguishable from ours, with a brain the same size as ours (slightly later on average iirc) and what they left, tools and paintings, look just like what we can do as well (behavioural modernity, thought to arise some time between -100 000 and -40 000).
You can find it hard to believe, but I think most people in that field agree that humans from the last 40 000 years would grow up as modern humans without problems.