Some see a slow progression in the accumulation of knowledge, while others see modern behavior evolving in fits and starts. Archaeologist Franceso d’Errico of the University of Bordeaux in France suggests certain advances show up early in the archaeological record only to disappear for tens of thousands of years before these behaviors—for whatever reason—get permanently incorporated into the human repertoire about 40,000 years ago. “It’s probably due to climatic changes, environmental variability and population size,” d’Errico says.
He notes that several tool technologies and aspects of symbolic expression, such as pigments and engraved artifacts, seem to disappear after 70,000 years ago. The timing coincides with a global cold spell that made Africa drier. Populations probably dwindled and fragmented in response to the climate change. Innovations might have been lost in a prehistoric version of the Dark Ages. And various groups probably reacted in different ways depending on cultural variation, d’Errico says. “Some cultures for example are more open to innovation.”
Perhaps the best way to settle whether the buildup of modern behavior was steady or punctuated is to find more archaeological sites to fill in the gaps. There are only a handful of sites, for example, that cover the beginning of human history. “We need those [sites] that date between 125,000 and 250,000 years ago,” Marean says. “That’s really the sweet spot.”
Erin Wayman writes Smithsonian.com's Homind Hunting blog.