Evolucion de los abuelos

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44 Scientific American, August 2011

Photograph by Tktk Tktk

© 2011 Scientific American

Rachel Caspari is a professor of anthropology at Central Michigan University. Her research focuses on Neandertals, the origin of modern humans and the evolution of longevity.

the evolution of grandparents
Senior citizens may have been the secret of our species’ success
By Rachel Caspari
IN BRIEFHUMAN ORIGINS

People today typically live long enough to become grandparents, but this was not always the case. Recent analyses of fossil teeth indicate that grandparents were rare in ancient populations, such as

those of the australopithecines and the Neandertals. They first became common around 30,000 years ago, as evidenced by remains of early modern Europeans. This surge in thenumber of seniors may have been

a driving force for the explosion of new tool types and art forms that occurred in Europe at around the same time. It also may explain how modern humans outcompeted archaic groups such as the Neandertals.

Illustration by Viktor Deak

August 2011, ScientificAmerican.com 45

© 2011 Scientific American

D

uring the summer of 1963, when i was six years old,my family traveled from our home in Philadelphia to Los Angeles to visit my maternal relatives. I already knew my grandmother well: she helped my mother care for my twin brothers, who were only 18 months my junior, and me. When she was not with us, my grandmother lived with her mother, whom I met that summer for the first time. I come from a long-lived family. My grandmother was born in 1895, andher mother in the 1860s; both lived almost 100 years. We stayed with the two matriarchs for several weeks. Through their stories, I learned about my roots and where I belonged in a social network spanning four generations. Their reminiscences personally connected me to life at the end of the Civil War and the Reconstruction era and to the challenges my ancestors faced and the ways they persevered.My story is not unique. Elders play critical roles in human societies around the globe, conveying wisdom and providing social and economic support for the families of their children and larger kin groups. In our modern era, people routinely live long enough to become grandparents. But this was not always the case. When did grandparents become prevalent, and how did their ubiquity affect humanevolution? Research my colleagues and I have been conducting indicates that grandparent-aged individuals became common relatively recently in human prehistory and that this change came at about the same time as cultural shifts toward distinctly modern behaviors—including a dependence on sophisticated symbol-based communication of the kind that underpins art and language. These findings suggest thatliving to an older age had profound effects on the population sizes, social interactions and genetics of early modern human groups and may explain why they were more successful than archaic humans, such as the Neandertals.
LIVE FAST, DIE YOUNG

the first step in figuring out when grandparents became a fixture in society is assessing the typical age breakdown of past populations—what percent werechildren, adults of childbearing age and parents of those younger adults? Reconstructing the demography of ancient populations is tricky business, however. For one thing, whole populations are never preserved in the fossil record. Rather paleontologists tend to recover fragments of individuals. For another, early humans did not necessarily mature at the same rate as modern humans. In fact,maturation rates differ even among contemporary human populations. But a handful of sites have yielded high enough numbers of human fossils in the same layers of sediment that scientists can confidently assess the age at death of the remains—which is key to understanding the makeup of a prehistoric group. A rock-shelter located in the town of Krapina in Croatia,

about 40 kilometers northwest of the...
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