Post by Admin on Jul 8, 2022 19:18:03 GMT
There is general agreement that their origins can be traced to a migration of Germanic-speaking people from mainland Northwest Europe that began in the early fifth century. But the number of individuals who settled in the British Isles and the nature of their relationship with the preexisting inhabitants, especially the Romano-British, is still unclear.
CONFLICTING EVIDENCE
Uncertainty persists because two of the main lines of evidence contradict each other. Historical documents such as Gildas’ The Ruin of Britain, Bede’s Ecclesiastical History of England, and The Anglo-Saxon Chronicle suggest not only that the incomers were numerous, but also that they more or less completely replaced the Romano-British, killing some and pushing the rest to the peripheries.
This picture is not supported by the results of isotopic analyses. Isotopes are different forms of a chemical element that can be distinguished by their atomic masses and physical properties. Isotopic analysis can help determine where an individual grew up.
When isotopes of strontium and oxygen extracted from Anglo-Saxon skeletons have been compared, they have pointed to only a few of the individuals having grown up in mainland Europe. This has been interpreted as evidence that the Romano-British were not replaced. Rather, they adopted a new language and set of values, beliefs, and cultural practices from a relatively small number of incomers.
Frustratingly, genetic studies have not been able to clarify the debate. They have returned such a wide range of estimates of the percentage of mainland European ancestry in England that they can support either hypothesis.
A NEW LINE OF EVIDENCE
Recently, we published a study in which we used a new line of evidence to investigate the issue: the three-dimensional (3D) shape of the base of the skull, which bioarchaeologists usually call the cranial base or basicranium.
Previous research has shown that when the basicranium is analyzed in 3D, its shape can be used to track relationships among human populations in a similar way to DNA. We reasoned that collecting such data from Anglo-Saxon skulls and comparing them to similar data from the two potential source regions might shed light on the composition of the Anglo-Saxon population.
Human cranial anatomy and the differential preservation of population history and climate signatures
Abstract
Cranial morphology is widely used to reconstruct evolutionary relationships, but its reliability in reflecting phylogeny and population history has been questioned. Some cranial regions, particularly the face and neurocranium, are believed to be influenced by the environment and prone to convergence. Others, such as the temporal bone, are thought to reflect more accurately phylogenetic relationships. Direct testing of these hypotheses was not possible until the advent of large genetic data sets. The few relevant studies in human populations have had intriguing but possibly conflicting results, probably partly due to methodological differences and to the small numbers of populations used. Here we use three-dimensional (3D) geometric morphometrics methods to test explicitly the ability of cranial shape, size, and relative position/orientation of cranial regions to track population history and climate. Morphological distances among 13 recent human populations were calculated from four 3D landmark data sets, respectively reflecting facial, neurocranial, and temporal bone shape; shape and relative position; overall cranial shape; and centroid sizes. These distances were compared to neutral genetic and climatic distances among the same, or closely matched, populations. Results indicate that neurocranial and temporal bone shape track neutral genetic distances, while facial shape reflects climate; centroid size shows a weak association with climatic variables; and relative position/orientation of cranial regions does not appear correlated with any of these factors. Because different cranial regions preserve population history and climate signatures differentially, caution is suggested when using cranial anatomy for phylogenetic reconstruction. Anat Rec Part A, 2006. © 2006 Wiley-Liss, Inc.
anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.a.20395
Our Anglo-Saxon sample comprised 89 individuals from five cemeteries in the English counties of Cambridgeshire, Suffolk, and Kent. Three of the cemeteries date to the early Anglo-Saxon period (A.D. 410–660) while the other two date to the middle Anglo-Saxon period (A.D. 660–889). We also collected data on 101 pre-medieval skeletons from two sites in Southern England and 46 individuals from various sites in Denmark that date to the Iron Age (800 B.C.–A.D. 399).
To obtain the landmark data, we employed a technique called photogrammetry. We imported 200 photos of each of the 236 skulls (minus the lower jaw) into a software program to create a high-resolution 3D model of each skull. We then used another software program to collect the 3D coordinates of a series of landmarks on the cranial base of each individual.
INDICATIONS OF MIXED ANCESTRY
Once we had collected the data, we used a set of statistical techniques called geometric morphometrics (GM) to identify similarities and differences in shape among the four groups: early Anglo-Saxons, middle Anglo-Saxons, pre-medieval British, and pre-medieval Danish.
Developed in the 1980s, GM has long been an important tool in the study of human evolution, but it has only recently been embraced by bioarchaeologists. GM allows patterns of shape variation to be investigated within a well-understood statistical framework and yields easily interpreted numerical and visual results. In our GM analyses, Anglo-Saxon skulls that shared more similarities with the pre-medieval British skeletons were considered to have local ancestry, while those that were more similar to the Danish skeletons were deemed to have mainland European ancestry.
The results we obtained suggested a substantial difference between the early Anglo-Saxon period sample and the middle Anglo-Saxon period. We found that between 66 percent and 75 percent of the early Anglo-Saxon individuals were of mainland European ancestry, while between 25 percent and 30 percent were of local ancestry. In contrast, we found that 50 percent to 70 percent of the middle Anglo-Saxon period individuals were of local ancestry, while 30 percent to 50 percent were of mainland European ancestry.
Shared descent for the Anglo-Saxons and the Vikings was not a requirement for membership in either group.While our estimates of the percentage of Anglo-Saxons who had mainland European ancestry fall comfortably within the range of estimates derived from genetic data, they contradict the picture painted by both the historical documents and the isotopic evidence. Specifically, our estimates suggest that there was greater persistence of the Romano-British population than the historical documents claim and a larger number of immigrants than the isotope evidence has been taken to indicate.
We think these discrepancies can be explained relatively easily. It seems likely that the mismatch between our results and the historical documents relates to the fact that the documents were written long after—in some cases, several hundred years after—the migration, and therefore are of questionable accuracy, which a number of scholars have argued.
We suspect the difference between our results and the isotopes may be the consequence of a misunderstanding. While strontium and oxygen isotopes are informative about where an individual grew up, they don’t tell us about a person’s ancestry. Hence, it is feasible that some, if not all, of the individuals with local isotopic signatures were second-generation immigrants—that is, their parents originated in mainland Europe but they themselves were born and raised in the British Isles.
CONFLICTING EVIDENCE
Uncertainty persists because two of the main lines of evidence contradict each other. Historical documents such as Gildas’ The Ruin of Britain, Bede’s Ecclesiastical History of England, and The Anglo-Saxon Chronicle suggest not only that the incomers were numerous, but also that they more or less completely replaced the Romano-British, killing some and pushing the rest to the peripheries.
This picture is not supported by the results of isotopic analyses. Isotopes are different forms of a chemical element that can be distinguished by their atomic masses and physical properties. Isotopic analysis can help determine where an individual grew up.
When isotopes of strontium and oxygen extracted from Anglo-Saxon skeletons have been compared, they have pointed to only a few of the individuals having grown up in mainland Europe. This has been interpreted as evidence that the Romano-British were not replaced. Rather, they adopted a new language and set of values, beliefs, and cultural practices from a relatively small number of incomers.
Frustratingly, genetic studies have not been able to clarify the debate. They have returned such a wide range of estimates of the percentage of mainland European ancestry in England that they can support either hypothesis.
A NEW LINE OF EVIDENCE
Recently, we published a study in which we used a new line of evidence to investigate the issue: the three-dimensional (3D) shape of the base of the skull, which bioarchaeologists usually call the cranial base or basicranium.
Previous research has shown that when the basicranium is analyzed in 3D, its shape can be used to track relationships among human populations in a similar way to DNA. We reasoned that collecting such data from Anglo-Saxon skulls and comparing them to similar data from the two potential source regions might shed light on the composition of the Anglo-Saxon population.
Human cranial anatomy and the differential preservation of population history and climate signatures
Abstract
Cranial morphology is widely used to reconstruct evolutionary relationships, but its reliability in reflecting phylogeny and population history has been questioned. Some cranial regions, particularly the face and neurocranium, are believed to be influenced by the environment and prone to convergence. Others, such as the temporal bone, are thought to reflect more accurately phylogenetic relationships. Direct testing of these hypotheses was not possible until the advent of large genetic data sets. The few relevant studies in human populations have had intriguing but possibly conflicting results, probably partly due to methodological differences and to the small numbers of populations used. Here we use three-dimensional (3D) geometric morphometrics methods to test explicitly the ability of cranial shape, size, and relative position/orientation of cranial regions to track population history and climate. Morphological distances among 13 recent human populations were calculated from four 3D landmark data sets, respectively reflecting facial, neurocranial, and temporal bone shape; shape and relative position; overall cranial shape; and centroid sizes. These distances were compared to neutral genetic and climatic distances among the same, or closely matched, populations. Results indicate that neurocranial and temporal bone shape track neutral genetic distances, while facial shape reflects climate; centroid size shows a weak association with climatic variables; and relative position/orientation of cranial regions does not appear correlated with any of these factors. Because different cranial regions preserve population history and climate signatures differentially, caution is suggested when using cranial anatomy for phylogenetic reconstruction. Anat Rec Part A, 2006. © 2006 Wiley-Liss, Inc.
anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.a.20395
Our Anglo-Saxon sample comprised 89 individuals from five cemeteries in the English counties of Cambridgeshire, Suffolk, and Kent. Three of the cemeteries date to the early Anglo-Saxon period (A.D. 410–660) while the other two date to the middle Anglo-Saxon period (A.D. 660–889). We also collected data on 101 pre-medieval skeletons from two sites in Southern England and 46 individuals from various sites in Denmark that date to the Iron Age (800 B.C.–A.D. 399).
To obtain the landmark data, we employed a technique called photogrammetry. We imported 200 photos of each of the 236 skulls (minus the lower jaw) into a software program to create a high-resolution 3D model of each skull. We then used another software program to collect the 3D coordinates of a series of landmarks on the cranial base of each individual.
INDICATIONS OF MIXED ANCESTRY
Once we had collected the data, we used a set of statistical techniques called geometric morphometrics (GM) to identify similarities and differences in shape among the four groups: early Anglo-Saxons, middle Anglo-Saxons, pre-medieval British, and pre-medieval Danish.
Developed in the 1980s, GM has long been an important tool in the study of human evolution, but it has only recently been embraced by bioarchaeologists. GM allows patterns of shape variation to be investigated within a well-understood statistical framework and yields easily interpreted numerical and visual results. In our GM analyses, Anglo-Saxon skulls that shared more similarities with the pre-medieval British skeletons were considered to have local ancestry, while those that were more similar to the Danish skeletons were deemed to have mainland European ancestry.
The results we obtained suggested a substantial difference between the early Anglo-Saxon period sample and the middle Anglo-Saxon period. We found that between 66 percent and 75 percent of the early Anglo-Saxon individuals were of mainland European ancestry, while between 25 percent and 30 percent were of local ancestry. In contrast, we found that 50 percent to 70 percent of the middle Anglo-Saxon period individuals were of local ancestry, while 30 percent to 50 percent were of mainland European ancestry.
Shared descent for the Anglo-Saxons and the Vikings was not a requirement for membership in either group.While our estimates of the percentage of Anglo-Saxons who had mainland European ancestry fall comfortably within the range of estimates derived from genetic data, they contradict the picture painted by both the historical documents and the isotopic evidence. Specifically, our estimates suggest that there was greater persistence of the Romano-British population than the historical documents claim and a larger number of immigrants than the isotope evidence has been taken to indicate.
We think these discrepancies can be explained relatively easily. It seems likely that the mismatch between our results and the historical documents relates to the fact that the documents were written long after—in some cases, several hundred years after—the migration, and therefore are of questionable accuracy, which a number of scholars have argued.
We suspect the difference between our results and the isotopes may be the consequence of a misunderstanding. While strontium and oxygen isotopes are informative about where an individual grew up, they don’t tell us about a person’s ancestry. Hence, it is feasible that some, if not all, of the individuals with local isotopic signatures were second-generation immigrants—that is, their parents originated in mainland Europe but they themselves were born and raised in the British Isles.