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First molars help trace how apes, humans evolved

The development of the first molars is closely attuned with basic aspects of a primate's biology, says a new study.

Washington, Dec 29 (IANS) The development of the first molars is closely attuned with basic aspects of a primate's biology, says a new study.

'Knowing the age when the first molar appears in the mouths of most primates allows researchers to predict a host of life history attributes,' says Gary Schwartz, associate professor in human evolution and social change at Arizona State University (ASU).


'Given that apes are our closest living relatives, understanding the broader context of when the characteristic developed is of great interest,' says Schwartz.


'We've known quite a bit about the timing of molar development in chimpanzees, which is important because they are our closest living relative.'


'However, we've known virtually nothing about when this important event occurs in other wild-living ape species - until now,' says lead study author Jay Kelley, research affiliate at ASU Institute of Human Origins.


Because of the difficulties in obtaining tooth emergence ages from animals in the wild, Kelley opted for other means; he searched for specimens in museums.


At the Zoologische Staatssammlung in Munich he found skulls of a wild-shot orangutan and gorilla that preserved emerging first molars.


'Like annual growth rings inside trees, the cells that produce teeth (both the enamel and underlying dentine) leave behind a trace of their presence, not as annual markers, but as growth lines that appear every day,' says Kelley.


By slicing the teeth in half, he and Schwartz were able to examine these incremental growth lines in ape individuals that died as their first molars were just erupting into their mouths.


Using this novel approach, the two scientists were able to mark the age of the gorilla's first molar emergence at 3.8 years, nearly identical to that of a wild chimpanzee's.


The orangutan's age at first molar emergence was surprisingly much later, at 4.6 years, which falls closer to the age of approximately six years in modern humans.


'We were excited to discover this much older age for the orangutan, since orangutans have much slower life histories than the other two great apes,' says Kelley.


However, Schwartz cautions that though the later emergence age in these large Asian apes is closer to that for modern humans, these latest findings should not be taken to indicate some special evolutionary relationship between the two.


These findings appeared in the December online edition of the Proceedings of the National Academy of Sciences (PNAS).


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