The earliest known cave paintings date from about 30,000 years ago, and the earliest bone tools found so far predate those paintings by another 40,000 years. Go back 100,000 years, and Homo sapiens — us lot — are only just emerging, though the fossil record suggests our ancestors back then had larger molars and thicker and heavier bones than we do.

How else would they differ from us?

Given a time machine, could we go back and communicate with them? Across such a vast temporal divide, would we be able to convey anything to them at all?