Researchers have long suspected there may be a biological reason for our desire to live long and prosper. Long life allows older people to share survival-enhancing information with the younger generation. Now, scientists have discovered a dramatic increase in longevity in Stone Age humans which, they say, might underpin the wave of population growth and cultural innovations that took place at that time.
Longevity is one of the traits that distinguishes humans from the great apes. Anthropologists have suggested several ways in which natural selection could have brought about that difference. The "grandmother hypothesis," for example, posits that increased longevity evolved because grandmothers can improve the survival of their children and grandchildren (ScienceNOW , 22 April 1998). But scientists lacked evidence that early humans lived longer than their hominid ancestors. In a study reported online in Proceedings of the National Academy of Sciences this week, anthropologists Rachel Caspari and Sang-Hee Lee of the University of Michigan and the University of California, Riverside, respectively, provide the missing data by aging fossil hominids from their teeth.
Caspari and Lee examined the teeth of 768 individuals from four hominid groups, ranging from the later australopithecines of 1.5 million to 3 million years ago to the Early Upper Paleolithic Europeans of 18,000 to 30,000 years ago. They calculated longevity as the ratio of old adults (30 years or more) to young adults (15 to 30 years) within a population, based on molar eruption and the degree of tooth wear. Across the four groups, longevity increased over evolutionary time. Most startling was a leap in longevity between Neandertals and Upper Paleolithic humans about 30,000 years ago
During the Upper Paleolithic, expanding human populations accompanied a "creative explosion," manifested in symbolic art, body ornaments, and exotic grave goods, says Caspari. "With longevity, you have the ability to transfer information across generations, and that's really important for human culture." And longevity promotes larger populations, in which "you have more opportunity for ideas to bounce around," she adds.
The massive jump in longevity between the Neandertals and Paleolithic humans "may explain why the Neandertals didn't do so well," says biological anthropologist Phyllis Lee of the University of Cambridge. Lee says the team's speculation that longevity played a role in the Upper Paleolithic revolution is reasonable, though she adds that more data are needed to clarify whether the longevity leap happened 30,000 years ago as Caspari and Lee suggest, or with the emergence and global spread of modern humans (Homo sapiens sapiens) 120,000 to 60,000 years ago.