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.
The work is based on the study of 390 skulls from the collection of skulls of the Catholic Church of Hallstatt (Austria).
Credit: University of Barcelona
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 Catholic Church ossuary; local tradition dictates that the remains of the town’s dead are buried but later exhumed to make space for future burials. The skulls are also decorated with paintings 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 inheritance of skull shape.
Credit: Universities of Manchester and Barcelona
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 skull in modern humans.”
Genetically determined morphological integration directs the evolution of skull shape in humans, according to an article published in the journal Evolution by a team including the experts Miquel Hernàndez, Neus Martínez-Abadías and Mireia Esparza, from the Anthropology Unit at the UB’s Department of Animal Biology. The study was also signed by Christian P. Klingenberg (University of Manchester), Torstein Sjövold (Stockholm University), Mauro Santos (Autonomous University of Barcelona) and Rolando González-José (Patagonian National Center, CENPAT-CONICET).
The study analyzes three-dimensional coordinates of 29 points distributed throughout the skull.
Credit: University of Barcelona
The study is based on the analysis of 390 skulls, decorated according to local tradition, from the ossuary in Hallstatt (Austria), which houses an exceptionally valuable collection for anthropological research. The more than 700 items of skeletal remains are famous for their painted decoration, depicting flowers, leaves and crosses, with the name of the deceased printed on the forehead of most of the skulls. By cross-referencing with local registers of births, deaths and marriages, experts have been able to use the collection to reconstruct the genealogical relationships of the population from as far back as the 17th century and make informed estimates of the influence of genes on skull shape.
A map with the coordinates of 29 anatomical landmarks According to the results of the study, the evolutionary potential of the human skull is formally constrained by the relatively high morphological integration of the different skull structures. “In this type of evolutionary scenario, it would be different to change or alter one element without also altering the others”, explains Miquel Hernàndez. “Traditionally, experts have studied how selection acts on a specific trait. In practice, however, the various traits are all inter-related. The key concept is morphological integration: if we change one of the elements in the shape of the skull the overall structure also changes, and only those changes that follow the morphological pattern are favoured”.
The researcher Neus Martínez-Abadías, first author of the study, explains: “One of the most innovative aspects of the study is the use of a methodology with which we can analyse the skull structure as a whole and quantify the impact of morphological integration. This means we are not obliged to study each trait separately as if evolution were a distributed process”.
The work is based on the study of 390 skulls from the collection of skulls of the Catholic Church of Hallstatt (Austria).
The Austrian skulls are part of a famous collection kept in the Hallstatt Catholic Church ossuary; local tradition dictates that the remains of the town’s dead are buried but later exhumed to make space for future burials. The skulls are also decorated with paintings 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 inheritance of skull shape.
Hallstatt, Austria
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 skull in modern humans.”
Genetically determined morphological integration directs the evolution of skull shape in humans, according to an article published in the journal Evolution by a team including the experts Miquel Hernàndez, Neus Martínez-Abadías and Mireia Esparza, from the Anthropology Unit at the UB’s Department of Animal Biology. The study was also signed by Christian P. Klingenberg (University of Manchester), Torstein Sjövold (Stockholm University), Mauro Santos (Autonomous University of Barcelona) and Rolando González-José (Patagonian National Center, CENPAT-CONICET).
The study analyzes three-dimensional coordinates of 29 points distributed throughout the skull.
The study is based on the analysis of 390 skulls, decorated according to local tradition, from the ossuary in Hallstatt (Austria), which houses an exceptionally valuable collection for anthropological research. The more than 700 items of skeletal remains are famous for their painted decoration, depicting flowers, leaves and crosses, with the name of the deceased printed on the forehead of most of the skulls. By cross-referencing with local registers of births, deaths and marriages, experts have been able to use the collection to reconstruct the genealogical relationships of the population from as far back as the 17th century and make informed estimates of the influence of genes on skull shape.
A map with the coordinates of 29 anatomical landmarks According to the results of the study, the evolutionary potential of the human skull is formally constrained by the relatively high morphological integration of the different skull structures. “In this type of evolutionary scenario, it would be different to change or alter one element without also altering the others”, explains Miquel Hernàndez. “Traditionally, experts have studied how selection acts on a specific trait. In practice, however, the various traits are all inter-related. The key concept is morphological integration: if we change one of the elements in the shape of the skull the overall structure also changes, and only those changes that follow the morphological pattern are favoured”.
The researcher Neus Martínez-Abadías, first author of the study, explains: “One of the most innovative aspects of the study is the use of a methodology with which we can analyse the skull structure as a whole and quantify the impact of morphological integration. This means we are not obliged to study each trait separately as if evolution were a distributed process”.
The first author of the study, Dr Neus Martínez-Abadías during the research work.
Credit: University of Barcelona
The experts applied geometric morphometric and quantitative genetic methods to examine human skull shape, using the three-dimensional coordinates of 29 anatomical ‘landmarks’ to create morphological maps and simulating a range of scenarios in which different key traits are selected during the evolutionary process of modern humans: the forward shift of the foramen magnum, flexion of the cranial base, retraction of the face and enlargement of the neurocranium. Although it was long believed that these traits evolve separately – through selection for bipedalism, dietary changes and encephalization – the results of this new study suggest that they are strongly integrated and that the developed of each trait may have favoured the evolution of the others. Individual traits do not evolve independently
The study calls for a reinterpretation of modern human evolutionary scenarios. As the lecturer Mireia Esparza explains, “Evolution acts as an integrated process and specific traits never evolve independently. In the case of the skull, evolutionary changes have converged to this morphological pattern. Therefore, we cannot simplify things and study the selection response of single trait in isolation, since although it is likely to have been affected by the selective factor in question, it is also constrained by the factors affecting other parts of the skull”. In human genealogies, each trait evolves gradually but within a pattern of strong morphological integration built on powerful genetic foundations.
“This functional, operational morphological pattern should not be considered a negative restriction. If we think about disorders affecting cranial development, for example, the pattern of integration could constrain the variation to keep it within the limits of a functional framework”, concludes the researcher Neus Martínez-Abadías. The study was conducted in association with the Catholic church of Hallstatt (Austria), the Wenner Gren Foundation for Anthropological Research (USA) and the Spanish Ministry of Education and Science.
The team composed of researchers Mireia Esparza, Miguel Nieves Martinez-Hernandez and Dr Neus Martínez-Abadías , Unit of Anthropology at the University of Barcelona.
Credit: University of Barcelona
The research, funded by the Wenner Gren Foundation for Anthropological Research (USA) and the Spanish Ministry of Education and Science, is published in the journal Evolution.
Contacts and sources:
Aeron Haworth
Faculty of Life Sciences
The University of Manchester
Universidad de Barcelona
Citation: 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
The experts applied geometric morphometric and quantitative genetic methods to examine human skull shape, using the three-dimensional coordinates of 29 anatomical ‘landmarks’ to create morphological maps and simulating a range of scenarios in which different key traits are selected during the evolutionary process of modern humans: the forward shift of the foramen magnum, flexion of the cranial base, retraction of the face and enlargement of the neurocranium. Although it was long believed that these traits evolve separately – through selection for bipedalism, dietary changes and encephalization – the results of this new study suggest that they are strongly integrated and that the developed of each trait may have favoured the evolution of the others. Individual traits do not evolve independently
The study calls for a reinterpretation of modern human evolutionary scenarios. As the lecturer Mireia Esparza explains, “Evolution acts as an integrated process and specific traits never evolve independently. In the case of the skull, evolutionary changes have converged to this morphological pattern. Therefore, we cannot simplify things and study the selection response of single trait in isolation, since although it is likely to have been affected by the selective factor in question, it is also constrained by the factors affecting other parts of the skull”. In human genealogies, each trait evolves gradually but within a pattern of strong morphological integration built on powerful genetic foundations.
“This functional, operational morphological pattern should not be considered a negative restriction. If we think about disorders affecting cranial development, for example, the pattern of integration could constrain the variation to keep it within the limits of a functional framework”, concludes the researcher Neus Martínez-Abadías. The study was conducted in association with the Catholic church of Hallstatt (Austria), the Wenner Gren Foundation for Anthropological Research (USA) and the Spanish Ministry of Education and Science.
The team composed of researchers Mireia Esparza, Miguel Nieves Martinez-Hernandez and Dr Neus Martínez-Abadías , Unit of Anthropology at the University of Barcelona.
The research, funded by the Wenner Gren Foundation for Anthropological Research (USA) and the Spanish Ministry of Education and Science, is published in the journal Evolution.
Contacts and sources:
Aeron Haworth
Faculty of Life Sciences
The University of Manchester
Universidad de Barcelona
Citation: 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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