Two-Million-Year-Old Tooth Widens the Ancient Human Family Tree

In a groundbreaking preprint paper, the secrets of four sets of two-million-year-old teeth have been unveiled through an innovative “proteomic” approach. Instead of relying on fragile DNA, which often disintegrates over time, the researchers analyzed the more robust protein molecules present in the teeth. The ancient dental remains were extracted from a sediment-filled cave in South Africa and belonged to an ancient hominin called Paranthropus robustus.

Despite being relatively small, measuring around three and a half feet tall and weighing approximately 100 pounds, P. robustus possessed a sturdy build. Although this species didn’t use stone tools, it exhibited resourcefulness by using bones for digging into termite mounds and its large teeth for chewing on tough foods like nuts.

Scientists attempting to construct a comprehensive family tree for early humans face significant challenges due to the scarcity of ancient DNA. Groundwater and high temperatures easily degrade such DNA, limiting its preservation to relatively recent periods. The oldest recovered African aDNA is about 18,000 years old, which pales in comparison to the timeline of human evolution that spans millions of years.

In 2010, researchers achieved a remarkable feat by sequencing the 400,000-year-old aDNA of a Neanderthal specimen from Spain, the oldest example of hominin aDNA to date. However, this represents only a small piece of the complex human family tree. Bipedalism, a defining characteristic of early humans, emerged around 4 million years ago, with the important precursor species Homo erectus evolving approximately 2 million years ago.

To overcome the limitations of ancient DNA, the recent study adopted a proteomic approach. The researchers extracted proteins from the enamel of the ancient teeth and analyzed them using mass spectrometry, resulting in a vast database of information. The team focused on a particular protein sequence with male and female forms, allowing them to distinguish between two males and two females among the specimens. This technique holds promise for future studies in which researchers aim to differentiate between species and sexes accurately.

Through their extensive proteomic analysis, the research team classified P. robustus as an outgroup in the clade that includes Homo sapiens, Neanderthals, and Denisovans. Notably, interbreeding between these groups has left traces of genetic material in modern-day humans.

The paper describes this work as a potentially transformative breakthrough for paleoanthropology, shedding new light on the early human family tree. However, the researchers stress the importance of further investigations involving the extraction of a broader range of proteins from various sources beyond tooth enamel. They suggest studying other early Pleistocene species like Australopithecus africanus and H. erectus to gain a deeper understanding of human evolution.

While this proteomic approach holds great promise, experts caution that analyzing bones might still be more reliable than analyzing proteins when it comes to clarifying complex family trees. Nonetheless, the study serves as a significant step forward in our quest to uncover the mysteries of our human ancestors. In 2020, proteins extracted from Homo antecessor tooth enamel demonstrated that this potential “missing link” species was related as a sister species, although not a direct antecedent to H. sapiens. As research continues, we can anticipate further exciting revelations about our ancient lineage.