Human skull study causes evolutionary headache

Dec 20, 2011

Scientists studying a unique collection of human skulls have shown that changes to the skull shape thought to have occurred independently through separate evolutionary events may have actually precipitated each other.

Researchers at the Universities of Manchester and Barcelona examined 390 skulls from the Austrian town of Hallstatt and found evidence that the human skull is highly integrated, meaning variation in one part of the skull is linked to changes throughout the skull.

The Austrian skulls are part of a famous collection kept in the Hallstatt ossuary; local tradition dictates that the remains of the town's dead are buried but later exhumed to make space for future . The skulls are also decorated with and, crucially, bear the name of the deceased. The Barcelona team made measurements of the skulls and collected genealogical data from the church's records of births, marriages and deaths, allowing them to investigate the of .

The team tested whether certain parts of the skull – the face, the cranial base and the skull vault or brain case – changed independently, as anthropologists have always believed, or were in some way linked. The scientists simulated the shift of the foramen magnum (where the spinal cord enters the skull) associated with upright walking; the retraction of the face, thought to be linked to language development and perhaps chewing; and the expansion and rounding of the top of the skull, associated with brain expansion. They found that, rather than being separate evolutionary events, changes in one part of the brain would facilitate and even drive changes in the other parts.

"We found that genetic variation in the skull is highly integrated, so if selection were to favour a shape change in a particular part of the skull, there would be a response involving changes throughout the skull," said Dr Chris Klingenberg, in Manchester's Faculty of Life Sciences

"We were able to use the genetic information to simulate what would happen if selection were to favour particular shape changes in the skull. As those changes, we used the key features that are derived in humans, by comparison with our ancestors: the shift of the foramen magnum associated with the transition to bipedal posture, the retraction of the face, the flexion of the cranial base, and, finally, the expansion of the braincase.

"As much as possible, we simulated each of these changes as a localised shape change limited to a small region of the skull. For each of the simulations, we obtained a predicted response that included not only the change we selected for, but also all the others. All those features of the skull tended to change as a whole package. This means that, in evolutionary history, any of the changes may have facilitated the evolution of the others."

Lead author Dr Neus Martínez-Abadías, from the University of Barcelona's, added: "This study has important implications for inferences on human evolution and suggests the need for a reinterpretation of the evolutionary scenarios of the in modern humans."

Explore further: Archaeologists, tribe clash over Native remains

More information: Martínez-Abadías, N.; Esparza, M.; Sjövold, T.; González-José, R.; Santos, M.; Hernàndez, M.; Klingenberg, C.P. "Pervasive genetic integration directs the evolution of human skull shape". Evolution, November 2011, DOI: 10.1111/j.1558-5646.2011.01496.x

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User comments : 3

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gunslingor1
not rated yet Dec 20, 2011
Nothing surprising to me in this story, life is adaptable. It's like anything really, like guitar for example. you Learn guitar, your body doesn't strengthen one finger at a time, then increase eye hand coordination, then so and so.... All these things occur in parallel. Even if you practiced really stringently to strength only one finger, you'd be strengthening the entire hand, improving accuracy and coordination all at once. Very similar here.

This study has zero effect on evolutionary theory.
JVK
1 / 5 (1) Dec 20, 2011
See also: http://www.physor...als.html

If the changes in the skull are driven by changes in the size of the olfactory bulbs, they present an even bigger challenge to those who think we are primarily visual creatures. Changes driven by the evolution of our olfactory acuity and specificity also rule out domain-specific modules, which never made scientific sense to me anyway -- even in theory.
jmhoward
1 / 5 (1) Dec 31, 2011
It is my hypothesis that human evolution resulted from selection for
testosterone: "Androgens in Human Evolution," Rivista di Biologia / Biology Forum 2001; 94: 345-362. (If your library does not subscribe to "Rivista ... ," you may read this at:
http://www.anthro...tion.htm . If you do not want to bother to visit this website, please, at least, note the chart from "General and Comparative Endocrinology" of 2003 which directly supports my explanation of human evolution. You may see the chart by going to the link above.)

My work concerning the effects of testosterone on human evolution may explain why "All those features of the skull tended to change as a whole package." ...including consequential changes in the body.

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