| The human brain governs a wide range of essential functions, comprising not only sensation and movement, but also thought, memory, and other advanced psychological functions. This powerful organ is the product of long-term evolutionary trends from our hominoid ancestors-Sahelanthropus tchadensis. Increasing cranial capacity has been considered to be an important feature of hominid evolution. With the increase in cranial capacity, the structure of the brain underwent changes; these included a rounded, widened frontal lobe, decreased size of the occipital lobe relative to the overall brain, a rounded cerebellum, and the drift of the two hemispheres of the cerebellum close to the median sagittal line.However, the proposed increase in cranial capacity during hominid evolution is now being challenged. Many recent studies indicate that trends in the evolution of the human brain changed slightly during the Holocene. The major change was towards a decrease in cranial capacity. From the Late Stone Age to modern times, the cranial capacities of Africans decreased by95-165cm3for males and74-106cm3for females. One study found that over the last35,000years, the average absolute brain size has decreased in Homo sapiens. Other studies suggested a decrease in endocranial volume between fossil AMH and recent humans. Chinese cranial and facial sizes decreased during Holocene, and that the head became progressively more globular after the Neolithic Age. Therefore, human brain during Holocene has been in constant change during Holocene. Since the global size reduction in H. sapiens was considered an exception to the trend toward brain size increase during hominin evolution, how the exception happened attracted our attention and what resulted in the decrease in cranial capacity became the primary objectives of our study. In addition, the human brain is composed of the cerebrum, cerebellum, and brainstem, which is subdivided into many smaller parts, respectively. Therefore, besides the decrease in the volume of every parts of the brain, the decrease in cranial capacity can be caused by one case that the volume of many parts of the brain decrease while other parts do not change or increase. Then how the structure of human brain changed with the decrease in cranial capacity became another major objective of our study.Since endocasts can reproduce details of external brain morphology, including cranial capacity and shape, they have played the most important role in the study of human brain evolution. To study the evolution of human brain during Holocene more clear, we collected the Neolithic human skulls unearthed from Beiqian sites which were identified by the Oriental Archaeology Research Center of Shandong University as being from the early Dawenkou period (about5500-6200years old) and modern-day human skulls. And the endocasts were reconstructed based on the CT data of these skulls and were measured using Amira software. We compared the three-dimensional computed tomographic reconstructions of endocasts taken from both Neolithic humans from Beiqian sites and modern-day humans for revealing the evolution of human brain during Holocene.Part1:Reconstruction of Neolithic endocasts from Beiqian sitesSection1:Morphological research on human skulls from Beiqian sitesObjective:The Neolithic human skulls unearthed from Beiqian sites were large in quantity and were nicely preserved, which were suitable for the morphological study. Identifying the age, sex, ethnic group, and deformation of each skulls can help studying the evolution of human brain during Holocene.Materials and methods:To address this issue, we chose81human skulls unearthed from Beiqian sites. The morphological observation and measurement of the skulls were finished according to methods from "Anthropometric Methods" and "Handbook of Anthropometry". The sex were identified by observing the morphology of skulls combined with discriminant analysis according to methods from "Sexual diagnosis of Chinese crania from discriminate function analysis" and "A study on the skulls from Taiyuan, Shanxi". The age was identified by observing the degree of the occlusal abrasion according to "Attrition of molar teeth in relation to age in northern Chinese skulls". The racial type was identified by comparing the morphology of Beiqian skull and modern Mongolian. The cranial CT images of Beiqian human and modern huamn were used for the three dimensional reconstruction by Amira software and the deformation of skulls were observed by comparing the3D reconstruction of Beiqian skulls and modern humans. Results:1. There were52male skulls and29female skulls.2. There were three age groups:young person (15-29years old), middle-younger person (30-44years old) and middle person (45-59years old). For male,12young person,20middle-younger person and20middle person were concluded. For female,11young person,13middle-younger person and5middle person were identified.3. The morphological features of Beiqian humans crania showed that the racial type of Beiqian people was closely related to the modern East Asiatic Mongoloids.4. The deformation of skulls generally happened in Beiqian skulls and modern people.Conclusion:On the whole, the culture of Beiqian site belonged to the Dawenkou culture and identification of age, sex, ethnic group of Beiqian skulls can help studying the evolution of human brain during Holocene.Section2:Sexual dimorphism and age-related changes in morphology of Neolithic endocasts from Beiqian sitesObjective:Because endocasts can reproduce details of external brain morphology and have played a vital role in research on the evolution of the human brain, it is necessary to reconstruct Neolithic endocasts from Beiqian sites and study their sexual differences and age-related changes, which could provide data set for studying human evolution.Materials and methods:81skulls which were identified as being from the early Dawenkou period were scanned by Siemens128Slice Computed Tomography (CT). All endocasts were reconstructed and placed in a standard spatial position, using Amira software. Standardized measurements and indices were taken to quantify the overall endocasts shape, including the length, breadth, height, cerebral height, frontal chord, frontal height, parietal chord and the ratios of breadth to length, height to breadth, height to length and frontal breadth to breadth of each endocast. All data were analyzed with SPSS17.0statistical software.Results:81Neolithic endocasts from Beiqian sites were reconstructed and measured, and12measurements and index were got. There were no sexual differences for the frontal chord, the ratios of breadth to length, height to breadth, height to length and frontal breadth to breadth, and the other7measurements had sexual differences. There were no age-related changes of endocasts for males and females.Conclusion:Neolithic endocasts from Beiqian sites can be reconstructed by segmenting cranial CT images and the sexual differences and age-related changes in morphology of Neolithic endocasts from Beiqian sites could provide data set for studying human evolution.Part2:Sexual dimorphism and age-related changes in morphology of modern Chinese endocastsObjective:Morphological observation and measurements of endocasts have played a vital role in researches on evolution of human brains. Because the age-related changes and sexual dimorphism in endocasts morphology can influence such investigations, it is necessary to reconstruct modern endocasts and study sexual dimorphism and age-related changes in endocasts morphology.Materials and methods:To address this issue, we conducted a systematic analysis of sexual dimorphism and age-related changes in modern Chinese endocasts. We collected the cranial computed tomography images of731modern humans, which were divided into four age groups:18-29years old,30-44years old,45-59years old, and60-74years old. After reconstructing virtual endocasts using Amira software, endocasts were placed in a standard position and standardized measurements and indices were taken to provide quantification of the overall endocast shape, including cranial capacity, the length, breadth, height, cerebral height, frontal chord, frontal height, parietal chord and the ratios of breadth to length, height to breadth, height to length and frontal breadth to breadth of each endocast. All data were analyzed with SPSS17.0statistical software.Results:1. The values for the main measurements of endocasts in different age groups for male and female were got.2. For most of measurements and indices, the males were larger.3. For males measurements, the height, frontal height, frontal chord and cerebral height didn’t change with increasing age, the length, parietal chord and the ratios of frontal breadth to breadth and height to breadth were positively correlated with age, while there were negative correlations between age and cranial capacity, breadth, frontal breadth, the ratio of breadth to length as well as height to length. For males relative measurements, the height and frontal chord didn’t change with increasing age, the length, parietal chord, cerebral height and frontal height were positively correlated with age, while there were negative correlations between age and breadth, frontal breadth. For females, the frontal chord didn’t change with increasing age, the length, parietal chord and the ratios of frontal breadth to breadth and height to breadth were positively correlated with age, while there were negative correlations between age and cranial capacity, breadth, height, frontal breadth, frontal height, cerebral height, the ratios of breadth to length as well as height to length.Conclusion:On the whole, there are significant sexual dimorphism and age-related changes in morphology of modern Chinese endocasts which should be taken into account in any research on endocasts.Part3:Increasing breadth of the frontal lobe but decreasing height of the human brain since the Neolithic PeriodObjective:Many recent studies indicate that trends in the evolution of the human brain changed slightly during the Holocene. The major change was towards a decrease in cranial capacity. However, there are no reports that how the human brain have evolved. Since endocasts can reproduce details of external brain morphology, including cranial capacity and shape, it is necessary to compare three-dimensional computed tomographic reconstructions of endocasts taken from both Neolithic and modern-day humans for revealing the evolution of human brain during Holocene.Materials and methods:To address this issue, we collected the cranial computed tomography images of modern adult humans, who were younger than60years of age. This sample comprised302men and209women. Then,81Beiqian skulls were scanned by Siemens128Slice CT, which included52males and29females. All the original CT data were imported into Amira software to obtain the three-dimensional skull and endocasts, which were placed in the standard position. The standardized measurements and indices were taken to provide quantification of the overall endocast shape, including cranial capacity, the length, breadth, height, frontal breadth and so on. All data were analyzed with SPSS17.0statistical software. Results:Various changes in the thirteen measurements and indices of the endocasts between our two samples were observed. The differences were statistically significant for cranial capacity, height, frontal breadth, length, the ratios of frontal breadth to breadth, height to breadth and height to length, frontal height, frontal chord and parietal chord between Beiqian humans and modern-day humans. On the contrary, there were no statistically significant differences for cerebral height, breadth, and the ratio of breadth to length between our two samples. After being scaled relatively to each individual’s cranial capacity, the differences were statistically significant for height, frontal breadth, length, frontal height, frontal chord, and parietal chord in males and the differences were statistically significant for height, frontal breadth, length and frontal chord in females between Beiqian humans and modern-day humans. The differences in sexual dimorphism were statistically significant for height, the ratios of height to breadth and height to length, frontal chord, parietal chord, and cranial capacity between Beiqian humans and modern-day humans. And what’s more, the levels of sexual dimorphism for these measurements and indices in modern-day humans are bigger than those in Beiqian humans, respectivelyConclusion:On the whole, cerebral structure has changed between two Chinese samples from Beiqian site and from living humans, and the main trends are the decrease in height and cranial capacity, and the increase in frontal breadth and sexual dimorphism. |
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