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Skull analysis reveals insights into human ancestry
By Tom Sherman, Daily Digest News Scientists recently concluded that humans experienced a relatively sharp drop in testosterone about 50,000 years ago, which aided in the cultivation of modern human civilization, by looking at human skulls.“Human fossils from after modern behavior became common have more feminine faces, and differences between the younger and older fossils are similar to those between faces of people with higher and lower testosterone levels living today,” said Robert Cieri, graduate biology student at the University of Utah and lead author of the paper, in a statement.
Heavy brows were out, rounder heads were in, and those changes can be traced directly to testosterone levels acting on the skeleton, according to Duke anthropologist Steven Churchill, who supervised Cieri while the student attended Duke.
Cieri compared the brow ridge, facial shape and interior volume of 13 modern human skulls older than 80,000 years, 41 skulls from 10,000 to 38,000 years ago, and a global sample of 1,367 20th century skulls from 30 different ethnic populations.
The trend that emerged was toward a reduction in the brow ridge and a shortening of the upper face, traits which generally reflect a reduction in the action of testosterone.
However, what the skulls do not reveal is whether the newly evolved humans produced and secreted less testosterone, or if they had fewer receptors for processing the hormone.
The feminization of facial structures and features due to lowered testosterone levels is in line with what has been established in non-human species. In a classic study of Siberian foxes, the animals that were less wary and less aggressive toward humans took on a different, more juvenile appearance and behavior after several generations of selective breeding.
“If we’re seeing a process that leads to these changes in other animals, it might help explain who we are and how we got to be this way,” said Brian Hare, animal cognition researcher at Duke University and co-author of the paper, in a statement. Scientists recently concluded that humans experienced a relatively sharp drop in testosterone about 50,000 years ago, which aided in the cultivation of modern human civilization, by looking at human skulls.
The study, titled, ‘Craniofacial feminization, social tolerance, and the origins of behavioral modernity’, was conducted by examining the shape and structure of skulls.
“Human fossils from after modern behavior became common have more feminine faces, and differences between the younger and older fossils are similar to those between faces of people with higher and lower testosterone levels living today,” said Robert Cieri, graduate biology student at the University of Utah and lead author of the paper, in a statement.
Heavy brows were out, rounder heads were in, and those changes can be traced directly to testosterone levels acting on the skeleton, according to Duke anthropologist Steven Churchill, who supervised Cieri while the student attended Duke.
Cieri compared the brow ridge, facial shape and interior volume of 13 modern human skulls older than 80,000 years, 41 skulls from 10,000 to 38,000 years ago, and a global sample of 1,367 20th century skulls from 30 different ethnic populations.
The trend that emerged was toward a reduction in the brow ridge and a shortening of the upper face, traits which generally reflect a reduction in the action of testosterone.
However, what the skulls do not reveal is whether the newly evolved humans produced and secreted less testosterone, or if they had fewer receptors for processing the hormone.
The feminization of facial structures and features due to lowered testosterone levels is in line with what has been established in non-human species. In a classic study of Siberian foxes, the animals that were less wary and less aggressive toward humans took on a different, more juvenile appearance and behavior after several generations of selective breeding.
“If we’re seeing a process that leads to these changes in other animals, it might help explain who we are and how we got to be this way,” said Brian Hare, animal cognition researcher at Duke University and co-author of the paper, in a statement.
Source: http://www.ascensionearth2012.org/2014/08/skull-analysis-reveals-insights-into.html
