Sometime around 35,000 years ago in Europe our ancestors embarked on what might be described as a creativity bender. They began making art, jewelry, musical instruments and complex tools in abundance, as evidenced by the remains of these items at sites across the continent. Archaeologists call this cultural period the Upper Paleolithic and it stands in marked contrast to the Middle Paleolithic that preceded it, during which anatomically modern humans and their archaic contemporaries, the Neandertals, focused their manufacturing efforts on a handful of relatively simple tool types. Experts have long debated exactly what sparked this creative explosion. As Central Michigan University paleoanthropologist Rachel Caspari describes in this article in the August issue, grandparents may have played a key role.

Today people routinely live long enough to become grandparents. But analyses of fossil teeth conducted by Caspari and her colleagues indicate that this is a relatively recent development. For most of human evolution, our ancestors mostly lived fast and died young. Reaching grandparent age, they show, did not become common until the Upper Paleolithic, and it may explain the sudden and dramatic shift in behaviors between the Middle and Upper Paleolithic. Having grandparents around in large numbers would have significantly increased population size, thus fostering innovation and self-expression, and it would have facilitated the transfer of valuable knowledge and cultural traditions to the next generation.

The symbolic objects and sophisticated implements of the Upper Paleolithic are not the oldest of their kind, however. In recent years researchers have discovered older examples at early modern human sites in Africa. Archaeologist Curtis Marean of Arizona State University in Tempe has found fancy tools and pigments presumably used for body paint at sites in Mossel Bay, South Africa, that date as far back as 164,000 years ago. At another site in South Africa called Blombos Cave archaeologist Christopher Henshilwood of the University of Bergen in Norway has recovered shell beads and engraved pieces of iron oxide as well as tools wrought from bone, dating back to 71,000 years ago. There are several such glimpses of modern behavior at sites in Africa and western Asia that precede the Upper Paleolithic by a long shot.

Neandertals also dabbled in such advanced practices on occasion. Several sites have yielded tools made by Neandertals using materials and techniques once attributed to anatomically modern humans alone. Our archaic cousins also had artistic leanings. For example, João Zilhão, an archaeologist at the University of Barcelona, has found in Spanish caves dating to nearly 50,000 years ago indications that the Neandertals there were wearing body paint and shell jewelry. And this past February Italian researchers reported that they had found evidence that 44,000 years ago Neandertals were harvesting wing feathers from a variety of birds at a site called Fumane Cave for decorative purposes. Experts refer to such decorations—along with sculpture, cave paintings and other art forms—as symbolic behaviors, which are a defining characteristic of the modern mind.

Although such examples of precociousness might seem to undermine Caspari's argument, they actually support it. The difference between these behaviors in the Middle Paleolithic (and its African equivalent, the Middle Stone Age) and the Upper Paleolithic is that in the former these traditions are relatively rare and fleeting, in the latter they are ubiquitous and sustained. The failure of these early glimmerings of art and sophisticated weaponry to spread and become permanent fixtures of the Middle Paleolithic and the Middle Stone Age seems to have been the result of small population sizes and local extinctions of these populations and their traditions. The Upper Paleolithic, with its burgeoning numbers of grandparents, allowed modern human behavior—the capacity for which arose long beforehand—to finally find a firm foothold.