molar size hominins

New study of molar size regulation in hominins

New study of molar size regulation in hominins

The Dental Anthropology Group at the CENIEH has tested the inhibitory cascade model to see whether it explains the size relationships and differences in shape between the different kinds of teeth, in the molar sample from the individuals identified at the Sima de los Huesos site in the Sierra de Atapuerca.
Mandíbula AT-1 de la Sima de los Huesos. Credits: Mario Modesto

The molar size relationship is one of the peculiar characteristics of the different species of hominins and various theories have been proposed to account for this, as well as the differences in shape between the different kinds of teeth (incisors, canines, premolars and molars). The latest theory, called the inhibitory cascade model, arose out of experiments with mice embryos, and in 2016 it was applied theoretically to fossil hominins, with satisfactory results.

It appeared that all hominins satisfy the inhibitory cascade model. In a paper by the Dental Anthropology Group at the Centro Nacional de Investigación sobre la evolución Humana (CENIEH), published recently in the Journal of Anatomy, this model was tested on the molar sample from the individuals identified at the Sima de los Huesos site, situated in the Sierra de Atapuerca (Burgos).

The results match the model generated in mice extraordinarily well, thus confirming the theory's utility once more. “Nevertheless, our conclusions have brought out an anomaly in the model, when it is applied to the oldest species of the genus Homo”, explains José María Bermúdez de Castro, Paleobiology Program Coordinator at the CENIEH and lead author of this work.

Increasing and decreasing patterns

In the genera Ardipithecus, Australopithecus and Paranthropus, as well as in Homo habilis, the size pattern is increasing and fits the premises of the inhibitory cascade model perfectly. The same thing happens in Homo sapiens, except that the pattern is decreasing, with the first molar larger than the second, which in turn is bigger than the third one (wisdom tooth).

Application of the inhibitory cascade model had led to the assumption that the switch from increasing to decreasing pattern would have arisen a little under two million years ago, perhaps coinciding with the transition between the genera Australopithecus and Homo. “However, in our work we noticed that this change could have required at least a million years to take place”, states Bermúdez de Castro.

The hominins from the Sima de los Huesos, which are around 430,000 years old, are a good example of that transition, whereas most specimens of Homo ergaster, Homo erectus, Homo antecessor and Homo heidelbergensis, as well as other species, do not fit the inhibitory cascade model. “Our idea is to continue our research to determine which genetic mechanisms lie behind this anomaly in the model”, says Bermúdez de Castro.

Full bibliographic information

Bermúdez de Castro et al. 2020. Testing the inhibitory cascade model in the Middle Pleistocene Sima de los Huesos (Sierra de Atapuerca, Spain) hominin sample. Journal of Anatomy. DOI: 10.1111/joa.13292
Press release from CENIEH.

The settlement of Europe could be the result of several immigration waves by a single population

The settlement of Europe could be the result of several immigration waves by a single population

The CENIEH conducts the morphological and metric analysis of the lower molars in the mandible from Montmaurin-La Niche (France) using micro-computed tomography, to study the origin of the Neanderthals.
settlement Europe immigration population
Montmaurin-La Niche mandible/M. Martínez de Pinillos

The Dental Anthropology Group of the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), in collaboration with the paleoanthropologist Amélie Vialet of the Muséum National d’Histoire Naturelle (MNHN) in Paris, has just published a detailed external and internal study of the molars in the mandible from the French site of Montmaurin-La Niche in the Journal of Human Evolution, whose results strengthen the hypothesis that the settlement of Europe could have been the result of several waves of migration at different times by a common source population.

The aim in this paper, led by the researchers Marina Martínez de Pinillos (CENIEH) and Laura Martín-Francés (CENIEH and PACEA-University of Bordeaux), is to shed light on the origin of the Neanderthals. The latest data obtained from paleontological and geomorphological studies place the Montmaurin-La Niche mandible in a chronologically intermediate position between the fossils of the Middle Pleistocene and the Neanderthals.

The micro-computed axial tomography (microCT) technique has enabled the molars in this mandible to be compared with the external and internal structures of over 400 other molars from the European, Asian and African Pleistocene and Holocene.

This exhaustive metric and morphological analysis has revealed that, while the mandible is more closely related to African and Eurasian populations from the Early and Middle Pleistocene, the enamel and dentine morphology and pulp cavity proportions are similar to those in Neanderthals. “Nevertheless, the absolute and relative enamel thickness values (2D and 3D) show greater affinity with those exhibited by certain Early Pleistocene hominins”, says Martínez de Pinillos.

Possible hybridization

Over recent decades, finds of human fossil remains from the European Middle Pleistocene have prompted the debate on the evolutionary scenario of the genus Homo on that continent to be reopened. “The great variability we find among the European Middle Pleistocene fossils cannot be ignored in studying human evolution on our continent”, states Martín-Francés.

This variability in European Middle Pleistocene populations could indicate different migrations at different times and/or fragmentation of the population, thought it might also be due to possible hybridization between residents and new settlers.

Montmaurin-La Niche mandible/M. Martínez de Pinillos

Full bibliographic information

Martínez de Pinillos, M., Martín-Francés, L., Bermúdez de Castro, J. M., García-Campos, C., Modesto-Mata, M., Martinón-Torres, M., & Vialet, A. (2020). Inner morphological and metric characterization of the molar remains from the Montmaurin-La Niche mandible: the Neanderthal signal. Journal of Human Evolution, 145, 102739. doi: 10.1016/j.jhevol.2019.102739.
Press release on the settlement of Europe due to immigration waves from a common source population from CENIEH

Environmental and climatic changes influenced the origin of the genus 'Homo'

Environmental and climate changes influenced the origin of the genus 'Homo'

CENIEH participates in a study on Mille-Logya, a new site located in the emblematic Afar region (Ethiopia), which reinforces the relationship between the origin of the Homo genus and the climatic and environmental changes that took place on the African continent between 2.5 and 3 million years ago
climatic changes Homo Mille-Logya
Hominin remains from the MLP area. Credits: Z. Alemseged et al

Several hypothesis suggest a link between the origin of the genus Homo and the climatic and environmental changes that took place in Africa between 2.5 and 3 million years ago. The geological and paleontological analyses of a new site, Mille-Logya, located in the emblematic region of Afar (Ethiopia) where the species Australopithecus afarensis was found, reinforces with new data these hypothesis.

A new study, published in Nature communication by an international team led by Zeresenay Alemseged from the University of Chicago, and with the participation of the geochronologist from the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), Mark Jan Sier, reports the finding of four hominin remains (two ulnae fragments, a calvarium fragment and an upper second molar) together with a large sample of faunal remains that include hypopothamus, bovids, giraffes, crocodiles, hyenas and horses.

The fossil samples come from three different areas, Gafura, Seraitu and Uraitele dated from 2.4 to 2.9 million years. “This site represents a unique opportunity to study fossils from an age range that normally is missing in the Afar area”, says Mark Jan Sier, from the Geochronology and Geology Programme of CENIEH and who contributed to the dating of the site with the paleomagnetic analysis.

The comparison of the fauna from the three different areas within Mille-Logya, as well as with that found in the nearby localities of Hadar and Dikika, where famous Australopithecus afarensis samples were found, suggests an important faunal and paleoenvironmental change during this period in this region of Africa.

The faunal and paleoenvironmental reconstructions suggest that the earliest members of Homo were associated with more open environments than Australopithecus was. The in situ faunal change at Mille-logya may be linked to environmental and climatic factors that may have caused Homo to emerge in from Australopithecus or to migrate to the region as part of a fauna adapted to more open habitats.

Full bibliographic information

Alemseged, Z., Wynn, J. G., Geraads, D., Reed, D., Barr, W. A., Bobe, R., McPherron, S. P., Deino, A., Alene, M., Sier, M. J., Roman, D., & Mohan, J. (2020). Fossils from Mille-Logya, Afar, Ethiopia, elucidate the link between Pliocene environmental changes and Homo origins. Nature Communications, 11, 2480. doi: 10.1038/s41467-020-16060-8.
Press release from CENIEH