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Did Grandma Supply the Competitive
Edge to Enhance Evolution?
July 6, 2004 New research says a dramatic
increase in human longevity about 30,000 B.C. provided the older, wiser
adults grandparents that propelled man along the evolutionary path.
The increase in longevity that occurred during the
Upper Paleolithic period among modern humans was dramatically larger
than the increase identified during earlier periods, the researchers
from the University of Michigan and the University of California at
Riverside claim.
Some scientists have long argued that the presence
of grandmothers confers an important evolutionary advantage since they
heavily invest their knowledge and other resources in their
reproductive-age daughters and their daughters offspring.
We believe this trend contributed importantly to
population expansions and cultural innovations that are associated with
modernity, these researchers wrote.
A large number of older people allowed early modern
humans to accumulate more information and to transmit specialized
knowledge from one generation to another, they speculated. Increased
adult survivorship also strengthened social relationships and kinship
bonds, as grandparents survived to educate and contribute to extended
families and others. Increased survivorship also promoted population
growth, the authors explain, since people living longer are likely to
have more children themselves, and since they also make major
contributions to the reproductive success of their offspring.
In their study of more than 750 fossils to be
published July 5 in the Proceedings of the National Academy of
Sciences, anthropologists Rachel Caspari and Sang-Hee Lee found a
dramatic increase in longevity among modern humans during that time: the
number of people surviving to an older age more than quadrupled.
Caspari, an assistant research scientist at the U-M
Anthropology Museum, said this increase in the number of relatively old
people likely had a major impact, giving modern humans a competitive
edge that ensured their evolutionary success.
For the study, the researchers analyzed the ratio
of older to younger adults in hominid dental samples from successive
time periods: later australopithecines, Early and Middle Pleistocene
Homo, Neandertals from Europe and Western Asia and post-Neandertal Early
Upper Paleolithic Europeans. They used a new analytical resampling
technique allowing them to assess the significance of differences in
rates of molar wear.
In the study, they defined old to be at least
double the age of reproductive maturation, which is also the time when
the third molars typically erupt. While the age of reproductive
maturation may have varied in early human groups, if it were 15, then
age 30 would be the age at which one could theoretically first become a
grandmother, Caspari noted.
By calculating the ratio of old-to-young
individuals in the samples from each time period, the researchers found
a trend of increased survivorship of older adults throughout human
evolution. Its not just how long people live thats important for
evolution, but the number of people who live to be old, Caspari and Lee
pointed out.
Significant longevity came late in human
evolution and its advantages must have compensated somehow for the
disabilities and diseases of older age, when gene expressions uncommon
in younger adults become more frequent, the authors noted.
There has been a lot of speculation about what
gave modern humans their evolutionary advantage, Caspari said. This
research provides a simple explanation for which there is now concrete
evidence: modern humans were older and wiser.
For more information on the U-M Anthropology
Museum, visit:
http://www.umma.lsa.umich.edu/
For the Proceedings of the National Academy of
Sciences, visit:
http://www.pnas.org |
