Early Signs of Prolonged Childhood: A Glimpse into the Lives of Early Homo
X-ray analysis of Dmanisi fossils reveals early signs of extended childhood in a member of the Homo genus.
Introduction: Uncovering Ancient Childhoods
The long, extended childhood characteristic of modern humans may trace its roots further back than previously thought, according to new research. Using advanced X-ray imaging to analyze the teeth of a young Homo individual from the Dmanisi site in Georgia, researchers have revealed1 a pattern of delayed, humanlike dental development followed by a growth spurt more typical of apes. This finding challenges the idea that prolonged childhood and slow development emerged only with later species of Homo, such as Homo sapiens.
The Dmanisi Fossils: A Unique Glimpse into Early Homo
The Dmanisi site, one of the oldest Homo fossil sites outside Africa, dates back between 1.77 and 1.85 million years. It holds an invaluable record of early Homo populations, preserving remains that provide insights into the anatomy, development, and behavior of ancient hominins. Among the five partial skulls found, a nearly complete juvenile skull allowed scientists to examine dental growth and development in ways not previously possible for early hominins of this age.
Some researchers classify the Dmanisi fossils as Homo erectus, while others regard them as an undetermined species within the Homo genus. Regardless, these fossils predate Homo sapiens by more than a million years and provide rare evidence of how early hominins may have developed and matured.
Dental Analysis Reveals Slow Start, Rapid Growth
To explore the development of this juvenile hominin, University of Zurich paleoanthropologist Christoph Zollikofer and his team used X-ray imaging to examine microscopic growth lines within the fossil teeth. The team focused on the development timeline of premolars and molars, reconstructing how these teeth grew and evolved over time.
"By studying these muscle attachment sites, we can reconstruct how muscles and ligaments were actively engaged throughout life, giving us a clearer picture of early hominin behavior," noted Zollikofer.
The results revealed a pattern of slowed growth from infancy until around age five, followed by a more rapid, chimplike pace of dental growth. This early slow development, according to Zollikofer and colleagues, hints at an initial evolutionary shift toward longer childhoods in early Homo. However, unlike modern humans, the Dmanisi juvenile experienced a faster burst of tooth development after age five, suggesting a blend of human and apelike growth patterns.
A New Perspective on Early Childhood in Homo
In contrast to Homo sapiens, where the maturation process—especially dental maturity—occurs between the ages of 18 and 22, the Dmanisi juvenile appears to have reached dental maturity by around 12-13 years. This timeframe is much closer to that of modern chimpanzees, which typically reach dental maturity between 11 and 13 years of age.
According to Zollikofer, the delayed start of dental development in the Dmanisi juvenile may represent an “evolutionary experiment” in prolonging childhood. If these early Homo individuals were direct ancestors of modern humans, he suggests that shared childcare practices, potentially including assistance from grandmothers and unrelated helpers, may have contributed to this early extension of childhood. Much later, further slowing in childhood growth in Homo sapiens may have coincided with increased brain size and complex social structures.
"If early Homo at Dmanisi belonged to a dead-end line, then Dmanisi looks like a first evolutionary experiment with extended childhood," Zollikofer proposed.
Variability in Early Childhood: Alternate Interpretations
The unique growth pattern observed in the Dmanisi fossils has prompted discussions on the factors that may have shaped early Homo childhoods. Kevin Kuykendall, a paleoanthropologist at the University of Sheffield, highlighted the significance of these findings as the first “fairly complete” reconstruction of an early hominin’s dental development. However, he cautions that this developmental pattern may not necessarily indicate an extended childhood.
Kuykendall notes that rather than shared childcare alone, other environmental and social factors, such as varying food availability or age at weaning, may have played a significant role in the dental development patterns observed in early Homo groups.
"Finding that a slow start to tooth growth did not substantially delay dental maturity could instead denote one of many ways in which tooth development evolved among ancient hominins," Kuykendall remarked.
An Evolutionary Experiment or Unique Adaptation?
Not all researchers agree on the interpretation that early Homo at Dmanisi experienced an extended childhood. Paleoanthropologist Tanya Smith of Griffith University expressed skepticism, pointing to the timing of the first molar eruption in the Dmanisi juvenile. Her research suggests that the first molar emerged at around 3.5 years, a timeline much closer to that of chimpanzees than humans.
According to Smith, the Dmanisi juvenile’s dental features align more closely with an apelike developmental trajectory than a human one. The combination of chimplike tooth eruption timing and a smaller brain size, Smith argues, points toward a faster, overall life history, rather than an extended childhood as seen in modern humans.
"Chimplike dental features of the Dmanisi youth are consistent with that individual’s small brain size, an even stronger indication of rapid overall development," Smith concluded.
The Broader Implications: Understanding the Evolution of Childhood
The Dmanisi juvenile’s unique pattern of slow early tooth development followed by rapid maturation offers new perspectives on the evolution of childhood in the Homo lineage. If the Dmanisi population represents an evolutionary experiment with prolonged development, it may provide clues about the early social and biological adaptations that laid the foundation for human life history traits. Shared childcare and a gradual increase in childhood length may have set the stage for the complex social behaviors that characterize modern human societies.
However, if the Dmanisi fossils represent a distinct evolutionary path, their unique growth patterns could illustrate one of the many developmental strategies that early Homo species used to survive and thrive in diverse and changing environments.
Whether a “dead-end” experiment or a precursor to the extended childhoods seen in modern humans, the Dmanisi fossils expand our understanding of the diverse developmental paths that early humans may have taken. By investigating these early signs of prolonged development, researchers continue to illuminate the many adaptive strategies that shaped our species.
Conclusion: The Complex Evolution of Human Childhood
The Dmanisi fossils offer a fascinating glimpse into the evolutionary origins of childhood in the Homo lineage, challenging the long-held assumption that prolonged childhood emerged only with later Homo species. As future studies examine additional fossil records, the variability and complexity of childhood growth patterns among early Homo species may provide further insights into how human social structures and life history traits evolved.
Zollikofer, C. P. E., Beyrand, V., Lordkipanidze, D., Tafforeau, P., & Ponce de León, M. S. (2024). Dental evidence for extended growth in early Homo from Dmanisi. Nature, 1–6. https://doi.org/10.1038/s41586-024-08205-2