A recent study, which meticulously analyzed an infant skeleton belonging to one of our ancient hominin relatives, indicates that Neanderthal babies might have been physically larger than their modern human counterparts during their early development.
While the behavioral and developmental milestones of Neanderthal infants, such as the age at which they began walking, remain subjects of unknown complexity, researchers note that these young individuals were characterized by substantial size and were not necessarily defined by excessive chubbiness.
Led by Ella Been of Ono Academic College in Israel, a team of colleagues undertook a comprehensive anatomical examination of a nearly complete skeleton. This specimen belonged to a Neanderthal infant who lived in the region now known as Israel between 51,000 and 56,000 years ago.
Unearthed in 1992 within a cave located 4 kilometers from the western shores of the Sea of Galilee, the infant is identified as Amud 7. The sex of this individual could not be definitively determined. Amud 7 represents one of a very limited number of juvenile Neanderthal remains discovered to date.
For several hundred thousand years, Neanderthals held prominence as the dominant hominin species across Eurasia. Their eventual extinction, which occurred approximately 40,000 years ago, is attributed to a combination of environmental shifts due to climate change and increased competition encountered with the burgeoning population of modern humans.
Based on the developmental stage of Amud 7’s teeth, specifically how the baby teeth had erupted, and microscopic analysis of the daily growth lines within the tooth enamel, researchers have estimated that the infant was likely around 6 months old at the time of death.
However, when considering bone length and the degree of brain development, Amud 7’s skeletal structure and cranial capacity more closely resemble that of a modern human infant aged between 12 and 14 months. This suggests a divergence where Amud 7 exhibited a younger dental age alongside a significantly more mature skeletal and neurological profile.
Been reported that when these findings from Amud 7 were compared with data from two other Neanderthal infant specimens—an approximately 2-year-old named Dederiyeh 1 from Syria and a 3-year-old discovered at Roc de Marsal in France—the same developmental pattern emerged.
“The consistent observation of this pattern across three distinct Neanderthal infants strongly suggests that it is not an isolated occurrence but rather a characteristic trait,” Been stated.
The primary challenge, as Been explained, lies in attempting to reconcile the developmental markers observed in Amud 7 and the other young Neanderthals with the expected growth trajectory of modern human infants.
Instead, the evidence points towards Neanderthal infants and modern human babies experiencing markedly different growth velocities. This disparity implies that younger Neanderthals likely had higher energetic requirements to fuel their accelerated development.
Interestingly, researchers noted that by approximately 7 years of age, these notable growth differences appeared to diminish, with children from both species subsequently following a more similar developmental path, according to Been.
When pressed to provide a definitive age for Amud 7, Been indicated a preference for the estimation derived from the dental evidence, rather than the skeletal data. “My assessment is that Amud 7 was closer to 6 months old,” she remarked. “During the initial few years of life, from birth through early childhood, Neanderthals demonstrated a faster rate of growth compared to modern humans.”
For Neanderthal infants, this accelerated growth was not necessarily linked to increased body fat. Been elaborated, “Small bodies with a high surface area-to-volume ratio, typical of newborns, tend to lose heat more rapidly. To prevent hypothermia, Neanderthals likely needed to gain weight and grow quickly. We observe a comparable phenomenon in Inuit babies, who exhibit rapid growth during their early years.”
Subsequently, the rate of Neanderthal physical growth slowed, and their final adult stature fell within the typical range for modern humans. However, Been added that they were generally on the shorter side.
Chris Stringer of the Natural History Museum in London commented on the significance of Amud 7, stating that the discovery helps fill a crucial void in our understanding of Neanderthal development.
“Synthesizing all available evidence,” Stringer explained, “researchers have identified three distinct growth phases in young Neanderthals. In newborns, both dental development and physical growth appear to align with a similar age, while brain development shows a notable advancement when compared to Homo sapiens.
“During infancy and toddlerhood, exemplified by individuals like Amud 7, there was a pronounced surge in both body mass and brain growth, contrasted with a comparatively slower pace of dental maturation,” Stringer continued. “However, in older children, dental and physical development subsequently synchronized, while brain growth continued at an accelerated rate.”