ASUDAS

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Reference plaques of the ASUDAS illustrating human tooth crown and root shape variants Reference plaques of the ASUDAS.png
Reference plaques of the ASUDAS illustrating human tooth crown and root shape variants

The ASUDAS (Arizona State University Dental Anthropology System) is a reference system for collecting data on human tooth morphology and variation created by Christy G. Turner II, Christian R. Nichol, and G. Richard Scott. [1] The ASUDAS gives detailed descriptions for common crown and root shape variants and their different degrees of expression. It also comprises a set of reference plaques illustrating dental variants as well as showing their expression levels in 3D. The ASUDAS was designed to ensure a standardized scoring procedure with minimum error in order to warrant comparability between data collected by different observers.

Contents

The ASUDAS currently comprises a set of 42 dental variants that can be observed in the permanent adult dentition. [2] The majority are crown and root shape variants, although the system also includes some skeletal variants of the maxilla and mandible. Most of the variants occur at different frequencies in human populations around the world. [3] Examples of dental variants listed in the ASUDAS are shovel-shaped incisors, Carabelli cusps, or hypocones.

Genetics

It is hypothesized that most of the dental variants listed in the ASUDAS are heritable and selectively neutral and that the worldwide dental diversity was generated by random evolutionary processes consisting of founder effects and genetic drift. [3] Several studies have also demonstrated that genetic distances across modern human populations derived from neutrally evolving SNPs or microsatellites are highly correlated with distances derived from dental variants listed in the ASUDAS. [4] [5] Additionally, dental variation within populations decreases with increasing geographical distance from Africa, [6] a signature also found in neutral genetic datasets as a result of a serial founder effect originating in Africa. [7]

Some dental variants listed in the ASUDAS are also likely to be associated with non-neutral evolutionary processes, such as natural selection. For example, shoveling and double-shoveling of upper first incisors and the presence of hypoconulids of lower second molars have been found to be linked to the ectodysplasin A receptor gene (EDAR). [8] [9] EDAR is a functional genomic region and has a range of pleiotropic effects on ectodermally derived structures, such as hair, mammary glands, and teeth, and is most likely under positive selection in Asian populations. [10] [11] It is possible that dental variants linked to EDAR are not direct targets of positive selection but rather 'hitchhiking' when selection acts on another phenotype. [9]

Applications

The enamel which covers a tooth crown is the hardest tissue in the human body and generally well preserved in taphonomic contexts, even when associated skeletal and DNA preservation is relatively poor. [3] Therefore, dental morphological data collected with the ASUDAS are commonly used for inferring the biogeographical origin of deceased humans when no other biological markers are available. For example, ASUDAS data are typically used for identifying unknown individuals in forensic cases, [12] for examining past migration and mobility in bioarchaeological contexts, [13] and for reconstructing hominin phylogenies in paleoanthropological studies. [14]

As a rule of thumb, dental inferences about neutral genetic affinities based on many ASUDAS variants are more reliable than those based on only a few variants. Nevertheless, the best performance is achieved when using specific combinations of highly diagnostic variants, and not the full ASUDAS set. [15]

A study conducted in 2023 found that ASUDAS variants are among the most informative morphological markers in the human skeleton for inferring underlying neutral genetic relatedness among populations, significantly outperforming other commonly employed data types, such as cranial non-metric and dental metric variables, for instance. [16]

Related Research Articles

<span class="mw-page-title-main">Neutral theory of molecular evolution</span> Theory of evolution by changes at the molecular level

The neutral theory of molecular evolution holds that most evolutionary changes occur at the molecular level, and most of the variation within and between species are due to random genetic drift of mutant alleles that are selectively neutral. The theory applies only for evolution at the molecular level, and is compatible with phenotypic evolution being shaped by natural selection as postulated by Charles Darwin.

Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.

<span class="mw-page-title-main">Negrito</span> Set of ethnic groups in Southeast Asia and Andaman islands

The term Negrito refers to several diverse ethnic groups who inhabit isolated parts of Southeast Asia and the Andaman Islands. Populations often described as Negrito include: the Andamanese peoples of the Andaman Islands, the Semang peoples of Peninsular Malaysia, the Maniq people of Southern Thailand, as well as the Aeta of Luzon, the Ati and Tumandok of Panay, the Mamanwa of Mindanao, and about 30 other officially recognized ethnic groups in the Philippines.

<span class="mw-page-title-main">Single-nucleotide polymorphism</span> Single nucleotide in genomic DNA at which different sequence alternatives exist

In genetics and bioinformatics, a single-nucleotide polymorphism is a germline substitution of a single nucleotide at a specific position in the genome that is present in a sufficiently large fraction of considered population.

<span class="mw-page-title-main">Directional selection</span> Type of genetic selection favoring one extreme phenotype

In population genetics, directional selection is a mode of negative natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype. Under directional selection, the advantageous allele increases as a consequence of differences in survival and reproduction among different phenotypes. The increases are independent of the dominance of the allele, and if the allele is recessive, it will eventually become fixed.

<span class="mw-page-title-main">Premolar</span> Transitional teeth located between the canine and molar teeth

The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered transitional teeth during chewing, or mastication. They have properties of both the canines, that lie anterior and molars that lie posterior, and so food can be transferred from the canines to the premolars and finally to the molars for grinding, instead of directly from the canines to the molars.

In anthropology, Sinodonty and Sundadonty are two patterns of features widely found in the dentitions of different East Asians. These patterns were identified by anthropologist Christy G. Turner II as being within the greater "Mongoloid dental complex".

<span class="mw-page-title-main">Jōmon people</span> Early inhabitants of prehistoric Japan

Jōmon people is the generic name of the indigenous hunter-gatherer population that lived in the Japanese archipelago during the Jōmon period. They were united through a common Jōmon culture, which reached a considerable degree of sedentism and cultural complexity.

Dual inheritance theory (DIT), also known as gene–culture coevolution or biocultural evolution, was developed in the 1960s through early 1980s to explain how human behavior is a product of two different and interacting evolutionary processes: genetic evolution and cultural evolution. Genes and culture continually interact in a feedback loop: changes in genes can lead to changes in culture which can then influence genetic selection, and vice versa. One of the theory's central claims is that culture evolves partly through a Darwinian selection process, which dual inheritance theorists often describe by analogy to genetic evolution.

<span class="mw-page-title-main">Human genetic variation</span> Genetic diversity in human populations

Human genetic variation is the genetic differences in and among populations. There may be multiple variants of any given gene in the human population (alleles), a situation called polymorphism.

<span class="mw-page-title-main">Black hair</span> Human hair color

Black hair is the darkest and most common of all human hair colors globally, due to large populations with this trait. This hair type contains a much more dense quantity of eumelanin pigmentation in comparison to other hair colors, such as brown, blonde and red. In English, various types of black hair are sometimes described as soft-black, raven black, or jet-black. The range of skin colors associated with black hair is vast, ranging from the palest of light skin tones to dark skin. Black-haired humans can have dark or light eyes.

<span class="mw-page-title-main">Shovel-shaped incisors</span> Possible shape of human incisor teeth

Shovel-shaped incisors are incisors whose lingual surfaces are scooped as a consequence of lingual marginal ridges, crown curvature, or basal tubercles, either alone or in combination.

In natural selection, negative selection or purifying selection is the selective removal of alleles that are deleterious. This can result in stabilising selection through the purging of deleterious genetic polymorphisms that arise through random mutations.

Ectodysplasin A receptor (EDAR) is a protein that in humans is encoded by the EDAR gene. EDAR is a cell surface receptor for ectodysplasin A which plays an important role in the development of ectodermal tissues such as the skin. It is structurally related to members of the TNF receptor superfamily.

The multiregional hypothesis, multiregional evolution (MRE), or polycentric hypothesis, is a scientific model that provides an alternative explanation to the more widely accepted "Out of Africa" model of monogenesis for the pattern of human evolution.

<span class="mw-page-title-main">Odontometrics</span> Measurement and study of tooth size

Odontometrics is the measurement and study of tooth size. It is used in biological anthropology and bioarchaeology to study human phenotypic variation. The rationale for use is similar to that of the study of dentition, the structure and arrangement of teeth. There are a number of features that can be observed in human teeth through the use of odontometrics.

<span class="mw-page-title-main">Maxillary lateral incisor agenesis</span>

Maxillary lateral incisor agenesis (MLIA) is lack of development (agenesis) of one or both of the maxillary lateral incisor teeth. In normal human dentition, this would be the second tooth on either side from the center of the top row of teeth. The condition is bilateral if the incisor is absent on both sides or unilateral if only one is missing. It appears to have a genetic component.

<span class="mw-page-title-main">Katerina Harvati</span> Greek paleoanthropologist

Katerina Harvati is a Greek paleoanthropologist and expert in human evolution. She specializes in the broad application of 3-D geometric morphometric and virtual anthropology methods to paleoanthropology. Since 2009, she is full professor and director of Paleoanthropology at the University of Tübingen, Germany. From 2020-2023 she was Director of the Institute for Archaeological Sciences and since 2023 she is Director of the Senckenberg Centre for Human Evolution and Palaeoenvironment at the University of Tübingen.

<span class="mw-page-title-main">Scandinavian Hunter-Gatherer</span> Archaeogenetic name for an ancestral genetic component

In archaeogenetics, the term Scandinavian Hunter-Gatherer (SHG) is the name given to a distinct ancestral component that represents descent from Mesolithic hunter-gatherers of Scandinavia. Genetic studies suggest that the SHGs were a mix of Western Hunter-Gatherers (WHGs) initially populating Scandinavia from the south during the Holocene, and Eastern Hunter-Gatherers (EHGs), who later entered Scandinavia from the north along the Norwegian coast. During the Neolithic, they admixed further with Early European Farmers (EEFs) and Western Steppe Herders (WSHs). Genetic continuity has been detected between the SHGs and members of the Pitted Ware culture (PWC), and to a certain degree, between SHGs and modern northern Europeans. The Sámi, on the other hand, have been found to be completely unrelated to the PWC.

<span class="mw-page-title-main">Near Eastern bioarchaeology</span> Archaeological sub-discipline

Near Eastern bioarchaeology covers the study of human skeletal remains from archaeological sites in Cyprus, Egypt, Levantine coast, Jordan, Turkey, Iran, Saudi Arabia, Qatar, Kuwait, Bahrain, United Arab Emirates, Oman, and Yemen.

References

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