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Ancient Footprints Reveal Coexistence of Early Human Species

Approximately 1.5 million years ago, two distinct species of early humans made their way across a muddy lakeshore in present-day Kenya, leaving behind footprints that offer groundbreaking insights into human evolution. A recent study published in the journal Science presents the first tangible evidence of multiple early human species existing in the same environment, a significant finding for paleoanthropology.

Tracy Kivell, a paleoanthropologist at the Max Planck Institute for Evolutionary Anthropology, describes the discovery as a “snapshot in time,” emphasizing how it challenges our understanding of early human interactions, as noted in remarks made to Nature News.

The two species in question are believed to be Homo erectus and Paranthropus boisei, leading to intriguing questions about their interactions. Briana Pobiner, a paleoanthropologist at the Smithsonian, points out the various possibilities: these two species may have competed for resources, cautiously observed one another from a distance, or even coexisted without bothering each other at all. Each option invites further speculation about their social dynamics during that era.

The fossilized footprints were discovered in July 2021 while researchers were excavating the eastern shore of Lake Turkana in a location known as Koobi Fora. Initially, the team uncovered a single hominin footprint along with some tracks likely made by large birds. The footprints were later protected with fine sand for further examination. In a follow-up excavation in 2022, researchers explored a larger area, uncovering a total of 12 footprints likely made by one individual, along with three additional isolated tracks from different individuals.

Along with these hominin tracks, the excavation yielded numerous wildlife footprints, including those of horse-like and cow-like animals. Remarkably, the discovery also included tracks from an extinct giant stork species, Leptoptilos falconeri, indicating a rich ecosystem existed at the time.

The researchers believe these footprints were formed at least 1.52 million years ago and were quickly covered by sand and sediment, preserving them remarkably well. The lack of cracking suggests minimal exposure to environmental elements, supporting the theory that the footprints were made in close succession.

Determining whether the footprints belonged to different species proved challenging at first. Traditional methods of matching skeletal remains to footprints were not applicable due to the limited fossil record. However, by employing advanced 3D imaging techniques and comparing the footprints’ anatomical features, the research team identified distinctions in gait and foot structure, concluding that at least two species cohabited the lakeshore.

The trail of 12 footprints is attributed to P. boisei, a species known for its strong jaw and large molars, which suggest a diet of tough plants and nuts. This hominin, characterized by a smaller brain and flat feet, went extinct several hundred thousand years after leaving these tracks, although the reasons for its extinction remain unclear.

The three isolated footprints, however, were likely made by H. erectus, which is recognized for its larger brain and more modern anatomical features. This species showcased adaptability in diet, utilized stone tools, and may have harnessed fire, allowing it to thrive for an additional million years after these footprints were left.

The skeletal remains of both H. erectus and P. boisei have been the only early hominin fossils found in the region, lending support to the hypothesis that they were the creators of the footprints. Fossil evidence also suggests that these two species might have shared the lakeshore environment for as long as 100,000 years, hinting at a possible coexistence where neither viewed the other as an immediate threat.

This coexistence could, in part, be understood through their dietary preferences. While H. erectus thrived on a versatile diet that included meat, P. boisei predominantly fed on grass-like plants, suggesting they might not have been in direct competition for resources. Bernard Wood, a paleoanthropologist, likens their relationship to sharing a convenient resource, akin to treating the lakeshore as a prehistoric marketplace.

Although the evidence suggests diverse dietary habits may have contributed to a peaceful coexistence, the possibility of competitive interactions cannot be dismissed entirely. There is also speculation about potential interbreeding between these species, paralleling the interbreeding known to have occurred among other hominins, but no definitive evidence has emerged to confirm such a relationship.

According to William Harcourt-Smith, a paleoanthropologist, human evolution illustrates a complex and non-linear history marked by experimentation. Understanding the interactions among these two species adds another chapter to the intricate story of early human evolution.

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