Hiroyuki Yamada

doi:10.19080/GJAA.2025.14.555886

Tooth Size Tells the Story of the Modern Human Journey

Hiroyuki Yamada

Department of Anatomy, School of Dentistry, Aichi-Gakuin University, Japan

Submission: April 10, 2025; Published: April 22, 2025

*Corresponding author: Hiroyuki Yamada Ph.D., Department of Anatomy, School of Dentistry, Aichi-Gakuin University, Nagoya 463-0013, Japan

How to cite this article:Hiroyuki Yamada. Tooth Size Tells the Story of the Modern Human Journey. Glob J Arch & Anthropol. 2025; 14(3): 555886. DOI: 10.19080/GJAA.2025.14.555886

Abstract

The size of the teeth of human groups from the Mesolithic to the present has been compared. The value is the sum of the average mesiodistal diameters of 14 measurements, from the central incisors to the second molars of the maxilla and mandible (TATS value). Human populations around the world have been divided into three groups (small, medium, large) based on the size of their teeth. The inhabitants of the African continent belonged to all three groups. The S group included Europe, the Middle East, West Asia, South East Asia, and North East Asia; the M group included South East Asia and East Asia; and the L group included Oceania, the Pacific Islands, and North and South America. Group S included areas around the African continent, and its distribution was similar to the route taken by early humans, so it was speculated that early modern humans who left Africa had small teeth. This distribution was also similar to the results of mitochondrial DNA analysis. It was thought that early modern humans left Africa and spread around the world, retaining their small teeth, and then developed medium to large teeth as they adapted to the climate, culture, environment, nutritional status, etc. of the regions in which they settled.

Keywords: Early Modern Humans; TATS Value; Small Tooth Size; Out of Africa

Tooth Size as represented by TATS Values

The morphology of teeth is strongly influenced by heredity and not much by the environment, so they have played an important role in anthropology. In particular, they have been used to analyse sexual dimorphism in fossil humans and for comparative analysis between populations in modern humans, and there are countless examples of their use [1-6]. Because they develop early in physical growth, teeth are less affected by the external environment, and the processes of growth and eruption are relatively stable, with minimal changes in tooth morphology. It is clear that tooth size is under the control of many genes [7]. Previous studies of tooth size have shown that between 54 and 78 per cent of crown size was due to genetic factors [8-11].

When crown size was analysed using principal component analysis, one of the multivariate analysis methods, the size factor and shape factor were extracted. The size factor accounted for more than 70% of the total information content of the measured items, and the shape factor accounted for the rest [12]. It has always been said that it is more appropriate to use shape factors than size factors for detailed comparison and analysis of the extent of spread, movement, and distribution of human populations [3, 13].

In modern dental anthropology, a factor such as tooth size has been downplayed when analysing population affinities.

However, it was thought that the effect of nutritional status on tooth size was minimal in prehistoric times, and also in historical times when society as a whole was poor and food supplies were not abundant. At the very least, there must have been no changes in the dietary environment that affected the size of a person’s teeth. Therefore, when studying a group of people based on the size of their teeth, it is impossible to ignore the existence of size factors that account for more than 70% of the information about the teeth. The main characterisation of each group on the basis of these size factors seems to be of great importance.

There was a study that calculated the total area (TS value: summary tooth size) of the dental crowns (mesiodistal diameter × buccolingual diameter) from the central incisors to the third molars in the upper and lower jaws to represent the total size as a representative value of tooth size [10]. However, because the TS value includes the highly variable third molars, and the labiolingual diameter of the anterior teeth in the mandible is prone to measurement error in plaster casts [14] (Mizoguchi, 1981), the author devised a new representative total mean value and compared the total size of the teeth in each group. The total average tooth size (TATS) used here is the sum of the average mesiodistal diameters of 14 measurements, from the central incisors to the second molars of the maxilla and mandible. In calculating the TATS, the sample size and standard deviation of each measurement were excluded and only the averages were used.

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The mesiodistal diameters of the dental crowns used were obtained from the Yamada (2018) database [15]. The TATS values for each human district/population/people are listed in the Appendix. By analysing tooth measurements using TATS values, this study aimed to infer the tooth size of modern humans who originating from Africa, and to find out the relationship between the tooth size of modern inhabitants spreading around the world and early modern humans when they migrated out of Africa (Figure 1).

Global distribution based on TATS values

The world population has been divided into three groups (S, M and L groups) on the basis of TATS values. These three groups have certain characteristics in common. The S group of small teeth with TATS less than 113 mm (white circle) included people from Africa, Europe, European Americans, people from the Middle East, the Ainu of Japan, some Chinese, Pakistanis, Bhutanese, Indians, Russians, and people living in South East Asia (Vietnamese, Indonesians, Bruneians, Filipinos, Negrito natives, etc.) and some Polynesians (prehistoric Hawaiians). Most were of European descent and some were of Asian descent.

People in group M, who had a TATS of 113 mm or more but less than 118 mm (gray circle), included people from East Asia and people living on some Pacific islands. This group included Japanese except the Ainu, Inuit from Canada and some Chinese, Koreans, Thais, Indonesians, some Polynesians (Cook Islanders), and Mexicans and some Africans. Most were Asian, but a few were Scandinavian, including Swedes and Finns.

Group L, with large-sized teeth measuring 118 mm or more (black circle), included the inhabitants of South and Central Africa, American blacks, Australian aborigines, the highlanders of New Guinea, and the islanders of Bougainville. There were also Polynesians (Fijians, Tongans, etc.) and Melanesians (Guamese, Palauans, etc.) from the South Pacific. The Native Americans who crossed the Bering Strait and expanded into the Americas also had large teeth, as did the indigenous South Americans. These groups included people of African and Asian descent, but mysteriously no Europeans (Figure 1).

Mother of the Human ancestral

Going back in time to the origin of modern humans, human fossils have been found in East Africa and it was generally accepted that they appeared around 200,000 years ago [16]. Early modern humans are originated in southern Africa, probably in the area around Botswana [17,18]. The Khoi and San (Khoisan) peoples of the Kalahari Desert in South Africa still maintain archaic forms of hunter-gatherer lifestyles and belong to the deepest lineage known to modern humans [19-21].

Looking at the distribution of tooth size among people living on the African continent, we could see that there was a mixture of people with small, medium, and large teeth [22-32]. Among them, the Khoisan had small teeth with a TATS value of 107.5 mm [33] to 113.7 mm [34,35]. The Mesolithic Nubians of Central Africa had large teeth measuring 119.0 mm [36], but the Nubians, who were agriculturalists from 3,300 B.C. to 1,100 B.C. and intensive agriculturalists from 1 A.D. to 1,400 A.D., were placed in the S group.

On the other hand, the oldest known human skull, dating from around 300,000 years ago, was discovered at the African Middle Stone Age (MSA) hominin site of Jebel Irhoud in Morocco, North Africa. The fossil was thought to represent an early stage in the evolution of Homo sapiens. The teeth were large, comparable in size to those of H. erectus, Neanderthals, and Archaic Middle Africans [22]. However, a tooth excavated from the Upper Palaeolithic Taforalt site in Morocco (150,000-20,000 BC) had a TATS of 114.7 mm [23], which was close to the S group.

Spreading from Africa to all over the world

There are two routes believed to have been open to modern humans to leave Africa: the Northern Route and the Southern Route. One of these routes is the Northern Route, which runs through the Sinai Peninsula towards Europe and Asia. In the Levant region along this route, fossils of modern humans dating from 177,000 to 194,000 years ago have been discovered in the Mishliya Cave in Israel [26]. In this photo you can see that the upper molars have degenerated. In addition, the third molars had two cusps mesially and the distal buccal and lingual cusps were missing. Despite the high degree of morphological degeneration, the size of the teeth in this specimen was almost the same as in Qafseh/Skull and Atapuerca (SH), indicating that they were large [26].

Teeth of 113.2 mm [23] have been recovered from the Natufian site in Israel (12,500 BC - 9,500 BC) and 110.0 mm [25] from the Druse site, indicating that most people in this region had small teeth. Even today, people from the Levant region had small teeth [24, 25]. The TATS value for modern Kurds (Turkey) people living in the north of this region was 109.0 mm [24]. Teeth of 111.8 mm [30] have been excavated from Mesolithic sites in Europe, 114.7 mm [38] from Early Mesolithic sites in Germany, and 105.9 mm [38] from Merovingian (5th-8th century) sites in France, all of which were small.

Another southern route starts in South East Africa and runs south from the Somali peninsula, through the Strait of Bab al- Mandeb to the Arabian Peninsula. It continues along the coast to India and South East Asia. The TATS value for the teeth of the Bedouin people in the area of the Arabian Peninsula was small at 112.5 mm [50], and the Yemenis also had small teeth at 106.2 mm [49] and 107.3 mm [24], and there were no people with large teeth in this peninsula. The small-toothed people spread east along the Indian Ocean from the coast of the Middle East, extending their distribution into South East Asia, then further south into Indonesia and north into North East Asia.

For example, small-sized teeth of 105.9 mm and 109.2 mm were found in Afghanistan [52], while in India the Punjabi had teeth of 112.6 mm [80] and the Hindus had teeth of 111.2 mm [79], the Tibetans in the Everest Mountains had teeth of 108.1 mm [81] and Bhutan had teeth of 107.9 mm [82]. The Andaman Islands in the Bay of Bengal had an average of 111.7 mm [13], Vietnam along the East China Sea 109.7 mm [50], Thailand in the Gulf of Thailand 112.6 mm [60] and 112.7 mm [68]. Teeth were also smaller in areas of North East Asia, including China. In China, Anyang (1,500 BC-1,027 BC) was 111.7 mm [60], Chifeng (1,027 BC-200 BC) 113.8 mm [60], Beijing 110.5 mm [66] and Yunnan 112.8 mm [65]. On the shores of Lake Baikal in Russia, Neolithic people had a TATS of 113.7 mm [5], and those living in the surrounding areas had small teeth of 110.8 mm [5] and 112.4 mm [54]. In North East Asia, teeth ranged from 109.4 mm to 112.2 mm [5].

After that, the teeth of the inhabitants who moved from South East Asia to Indonesia, and then to New Guinea and Australia, became larger. The people who moved to the remote Oceania region of the South Pacific also had large teeth. Large teeth were also found in the populations that migrated to the Americas. These distributions due to the TATS values were also similar to the results of mitochondrial DNA analysis [27]. It is thought that early modern humans left Africa and spread around the world, retaining their small-sized teeth, and then developing mediumto large-sized teeth as they adapted to the climate, culture, environment, nutrition, etc. of the regions in which they settled.

Acknowledgements

This research is based on a large amount of valuable dental measurement data collected from human populations around the world. I would like to express my sincere gratitude to the researchers who worked to collect this dental measurement data.