The discovery of hominid teeth in the Yanhui Cave, located in Tongzi, Southern China, has sparked a significant breakthrough in the study of human evolution. These four teeth, found between 1972 and 1983, have been the subject of an extensive comparative research project, shedding new light on the human populations that existed during the Late Middle Pleistocene period. The latest findings suggest that these teeth do not fit the morphological pattern typically associated with Homo erectus, a species long considered a key player in human evolution. Instead, the teeth may represent another group of hominids, possibly linked to the elusive Denisovans, a mysterious population of humans that has intrigued researchers for years.
This research, led by scientists María Martinón-Torres and José María Bermúdez de Castro from the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), has been published in the Journal of Human Evolution. Their study not only challenges the traditional understanding of human evolution but also opens the door to new possibilities regarding the diversity of hominid species in East Asia during the Middle Pleistocene.
Discovery of the Tongzi Teeth
The teeth found in the Yanhui Cave were initially thought to belong to either late Homo erectus or early Homo sapiens, based on their chronology, which places them between 172,000 and 240,000 years old. These dates suggest that the teeth belonged to hominids who lived during a time when multiple human species coexisted in different parts of the world. However, the results of the recent study, which involved advanced methods such as geometric morphometrical analysis and Micro-Computed Tomography (micro-CT), have raised significant questions about the initial classification of these teeth.
The analysis revealed that the morphology of the Tongzi teeth does not align with the traditional features associated with Homo erectus. Instead, they display traits that are more consistent with populations related to the Denisovans, a group of ancient humans whose genetic legacy has been discovered but whose physical appearance remains largely unknown.
The Denisovans are a group of hominids whose existence was first confirmed in 2010 through the genetic analysis of a phalanx bone and a tooth found in the Denisova Cave in the Altai Mountains of Russia. Although only a small number of Denisovan fossils have been found, their genetic imprint is present in the genomes of modern humans, particularly among populations in Asia and Oceania, suggesting that they interbred with ancestors of these groups.
The Significance of the Research
This new study challenges previous assumptions about the hominid populations of East Asia during the Middle Pleistocene. Until now, it was widely believed that the region was primarily inhabited by Homo erectus, with limited interaction from other hominid species. However, the findings from Tongzi suggest that there may have been at least two distinct human populations coexisting in East Asia at this time. One group, which could be classified as Homo erectus, would be represented by fossils from sites like Zhoukoudian, Hexian, and Yiyuan. This group would exhibit the typical traits of Homo erectus, such as larger, more robust teeth and a generally more primitive cranial structure.
The second group, however, may represent a more derived lineage, exhibiting characteristics that are more commonly associated with later species of the Homo genus, such as Homo sapiens. These features include greater crown symmetry, a simplified dentine surface of the third premolar, and evidence of tongue thrusting. These traits align more closely with those observed in Denisovans, suggesting that the population represented by the Tongzi teeth could potentially be part of this enigmatic group.
One of the key researchers involved in this study, María Martinón-Torres, emphasizes that more genetic and fossil discoveries will be necessary to definitively classify the Tongzi hominids and determine their relationship to other populations. She suggests that these hominids could be excellent candidates for Denisovan ancestry, though more evidence is needed to fully evaluate their place within the broader landscape of human evolution.
Who Were the Denisovans?
The Denisovans are a mysterious branch of archaic humans that were first identified through the genetic analysis of remains discovered in the Denisova Cave in Siberia. The initial discovery of their existence came in 2010 when scientists extracted DNA from a fragment of a finger bone and a tooth found in the cave. Subsequent genetic analysis revealed that the Denisovans were closely related to Neanderthals, another group of archaic humans, but they were distinct from both Neanderthals and modern humans.
Although very few fossil remains of the Denisovans have been found, genetic evidence suggests that they were a widespread group, likely inhabiting parts of Asia and Oceania. In fact, many modern populations in these regions carry traces of Denisovan DNA, indicating that there was likely interbreeding between Denisovans and early Homo sapiens in these areas. For instance, populations in Papua New Guinea and Australia possess a significant percentage of Denisovan ancestry, contributing to their unique genetic characteristics.
Despite the genetic data, much about the Denisovans remains a mystery. Their physical appearance, cultural practices, and behavior are still largely unknown, as there are only a few fossilized remains attributed to them. This lack of physical evidence has made it challenging for scientists to form a comprehensive picture of who the Denisovans were. However, the recent discovery of the Tongzi teeth provides an intriguing clue that these enigmatic hominids may have left a more extensive footprint in East Asia than previously thought.
Implications for Human Evolution
The findings from the Tongzi teeth are part of a growing body of evidence suggesting that human evolution was not a simple, linear process but rather a complex web of interrelated species, many of which coexisted and interacted with one another. The existence of multiple hominid populations in East Asia during the Middle Pleistocene period, including the possibility of Denisovans, suggests that our ancestors were part of a much larger and more diverse evolutionary landscape than we once imagined.
The idea that the Denisovans may have had a more widespread presence in East Asia during this period challenges the traditional view that Homo erectus was the dominant human species in the region. It also raises important questions about the interactions between these different groups. Were there significant interactions between Denisovans and Homo erectus? Did these populations interbreed, and if so, to what extent? These are questions that future research may help to answer.
Furthermore, the discovery of Denisovan traits in the Tongzi teeth adds to the growing body of evidence that human evolution was shaped by a dynamic interplay of different hominid populations. The idea that Denisovans may have contributed to the genetic makeup of modern human populations adds a new layer to our understanding of human ancestry, highlighting the complexity and diversity of our evolutionary past.
More information: Song Xing et al. Late Middle Pleistocene hominin teeth from Tongzi, southern China, Journal of Human Evolution (2019). DOI: 10.1016/j.jhevol.2019.03.001