Since physical changes have been documented in these Asian populations, principal components analyses were conducted for certain variable groupings in each population to understand how crania shape were related. Based on visual inspection, ancient crania appears to be long and narrower compared to their more modern counterparts, and these tests will illustrate which portions of the crania are changing over time.p. 181:
Since physical differences were shown to be present between the two ethnic groups, shape and size changes were calculated to understand how the crania have changed over time. Principal components analysis was calculated using transformed log variables of the dataset to determine which measurements were changing. All populations appeared to be extremely divergent from one another, resulting in unequal variancecovariance matrices. Modern Chinese individuals appear to have a shorter head than their ancient counterpart while modern Thais tend to have narrower faces and heads than their ancestral group.p. 187:
None of the variable groupings show a close biological relationship between modern populations. However, the modern Thai population did show a closer biological relationship with the modern Chinese than with either archaeological population. One possible reason for this outcome is due to the influx of Chinese immigrants to Thailand that eventually became part of the gene pool. However, gene flow did not work in reverse with Thai people moving into China. For the most part Thai people remained ethnically Thai and Chinese people remained Chinese.p. 197:
Modern Chinese individuals appear to have narrower and longer crania, which is opposite than expected. Ancient Chinese crania have higher cranial vaults than their modern counterparts, which contributes to their divergence. Facial variables that appear to be most divergent are ones that measure for prognathism and upper facial height. Modern Chinese individuals have longer upper facial height but are not as prognathic as their ancient counterparts.
Craniofacial Differences Between Modern and Archaeological Asian Skeletal Populations
Chan, Wing Nam Joyce
The principal objective of this study is to perform a biological distance analysis of two Asian ethnic groups to better understand environmental factors influencing cranial shape and size. Cranial shape and size are influenced by both epigenetic and genetic factors, resulting in differences in crania over time. Cranial measurements can be used as a proxy for genetic data and to understand epigenetic factors affecting crania. Therefore, craniometrics can be used to determine differences between populations.
Ancient and modern Chinese and Thai skeletal populations were used for this biological distance analysis. The ancient Chinese population is from northern China at Anyang dating to the Shang Dynasty (1600BC-1046BC) while its modern counterpart is located in Hong Kong dating from 1977-1983. Individuals from both populations are thought to have belonged to the Han ethnic group and are possibly biologically related. Both Thai populations are located in northeastern Thailand, known as the Isaan region. The ancient Thai population from the Ban Chiang site is dated through the Pre-metal to Iron Age periods (2000 B.C.- 200 A.D.) while the modern population dates from 1970s to present. Data were collected on crania at 29 anthropologically accepted measurements to explore epigenetic and biological relationships between modern and ancient populations. Data were subjected to multiple multivariate statistical tests to understand causative agents for change and differences between populations.
These results suggest that modern and ancient Thai and Chinese populations have markedly different crania, especially in shape. However, correlated factors could not be identified in this study, primarily due to lack of historical data. Geographical, temporal, and climate variables such as temperature were tested against measures of biological distance with little to no correlation discovered. Interestingly, modern and ancient Chinese populations displayed the closest biological affinity, possibly due to similar environments and lack of genetic changes. Ban Chiang individuals were the most biologically distant from other populations, indicating possible genetic differences not yet understood. These genetic differences could indicate either that Ban Chiang individuals are not recently ancestral to the modern Thai population or a mass migration movement into northeast Thailand had occurred.
These results are interpreted to indicate that environmental factors have played a large role in altering cranial shape in these two ethnically Asian populations since genetic alteration in the areas has not been documented. Environmental factors have caused isometric changes in cranial shape as crania have become distinct from their ancestral counterparts. Cultural changes, such as diet shifts and modernization, are possible causative agents for these changes witnessed in these populations.
The findings of this study contribute to our understanding of human cranial variation for these two Asian groups, and to broader discussions of epigenetic and genetic relationships in the expression of cranial morphology. This research also contributes to the discussions of how biological distance in the crania has been influenced by epigenetic factors and ultimately how the peopling of modern Asia occurred.