Emiliano Bruner, a paleoneurologist at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), has contributed significantly to a recent study published in Quaternary International that sheds new light on the anatomy of the temporal lobes in Homo erectus. This study provides evidence that the temporal lobes of H. erectus were proportionally smaller than those of modern humans, marking a key distinction in the evolution of the human brain.
The temporal lobes are integral to various cognitive functions, including memory, emotion, hearing, social interaction, and language. They are located in a delicate region of the brain known as the middle cranial fossa, which is often poorly preserved in fossilized specimens. This has made it particularly challenging to study the anatomy of the temporal lobes in extinct human species. While we have detailed knowledge of the temporal lobes in Homo sapiens—where they are relatively more developed than in other primates—understanding their size and function in earlier human species has remained elusive.
Earlier research by Bruner and his colleagues established that the size of the middle cranial fossa can be used to infer the volume of the temporal lobes in fossil hominins. Building on this, the new study expanded upon these methods by analyzing three key anatomical diameters in fossil skulls of H. erectus and H. ergaster and comparing them with similar measurements from 51 modern human skulls. The findings reveal a clear difference between fossil species and modern humans, with both H. erectus and H. ergaster showing temporal lobes that were smaller in proportion to their brain size compared to contemporary humans.
An intriguing aspect of the study is the difference observed between the two species of Homo examined. The research suggests that Homo erectus from Asia had larger temporal lobes than Homo ergaster, the African counterpart. This finding raises the possibility of geographical variation in brain development within early human species, although the relatively sparse fossil record means it is unclear whether this difference is significant or simply a result of chance. As Bruner notes, “the scanty fossil record does not allow us to tell whether this is due to chance or a paleoneurological difference between the two species.”
The significance of this study extends far beyond simple anatomical comparisons. The temporal lobes play a crucial role in a wide array of cognitive functions, and any variation in their size or structure could indicate differences in the mental and neural capabilities of early humans. This includes functions such as processing auditory information, managing social interactions, and controlling memory—essential aspects of human behavior. If the temporal lobes were smaller or differently structured in H. erectus compared to modern humans, it could suggest a different pattern of brain development and possibly a divergence in cognitive abilities between these early human species and us.
In particular, the study highlights the potential importance of the temporal lobes in understanding the evolution of complex human behaviors. Changes in the size or structure of these lobes could be linked to the evolution of language, social cognition, and even emotional processing, areas that are key to distinguishing modern humans from other species. Since the temporal lobes are central to processing sensory information and forming memory, any modification in their development over time could offer valuable insights into the mental capacities of ancient human populations.
The research team’s methodology, comparing fossil measurements to modern human data, provides a more precise understanding of how the brain of early human species evolved. While the temporal lobes are often difficult to study due to the fragile nature of the fossils, the approach taken by Bruner and his colleagues represents an innovative way of bridging the gaps in our understanding of hominin brain anatomy. By examining fossil skulls through the lens of modern neuroanatomy, researchers can extrapolate insights about the cognitive abilities of extinct species, helping to paint a clearer picture of human evolution.
Ultimately, this study contributes to a growing body of evidence that underscores the complexity of human brain evolution. While Homo erectus and H. ergaster were certainly advanced in many respects, the structural differences in their temporal lobes may reflect fundamental differences in their cognitive abilities compared to modern humans. As the field of paleoneurology continues to evolve, studies like this provide crucial pieces of the puzzle, helping us understand not just the physical, but also the cognitive evolution of our ancient ancestors.
More information: Alannah Pearson et al. Temporal lobe evolution in Javanese Homo erectus and African Homo ergaster: Inferences from the cranial base, Quaternary International (2020). DOI: 10.1016/j.quaint.2020.07.048