For the first time, scientists identified the sex of a 3.5-million-year-old Australopithecus africanus using ancient proteins, marking a milestone in the field of paleoanthropology. The study, published in the South African Journal of Science, reports that the fossil remains and the tooth of Australopithecus africanus belong to a male individual.
The fossilized remains were discovered in the Sterkfontein Caves in South Africa, a site renowned for its wealth of hominid fossils. These caves are part of the Cradle of Humankind, a UNESCO World Heritage Site that has yielded fossils from at least six hominin species, including Australopithecus africanus and Homo naledi. The Australopithecus africanus remains have been dated to more than three million years old, making the discovery particularly noteworthy.
The analysis was achieved through the use of paleoproteomics, a technique that involves the extraction and analysis of ancient proteins. One protein in particular, amelogenin, which plays a key role in tooth development and is produced differently in males and females, was the focus of the researchers. By analyzing the molecular structure of amelogenin, they were able to determine the sex of the Australopithecus africanus individual.
"To my knowledge, among the publicly shared hominin enamel proteomes, A. africanus is the oldest hominin to be subjected to palaeoproteomic analysis," said Palesa Madupe of the University of Copenhagen, the lead scientist of the team, according to Archaeology Magazine. Madupe emphasized the importance of this advancement in the field of human evolution studies.
The research team employed a minimally invasive technique to extract and analyze over 100 peptides from the tooth enamel of an Australopithecus africanus specimen found in the Sterkfontein Caves. Among the 118 peptides recovered from the tooth, some were unique to amelogenin. The gene that encodes amelogenin has two different versions: AMELX and AMELY, found on the X and Y sex chromosomes, respectively. AMELX and AMELY lead to the production of slightly different forms of the amelogenin protein. The presence of AMELY peptides indicates that an individual has a Y chromosome, allowing scientists to infer the individual's sex. In the case of the Australopithecus africanus specimen, the researchers identified four peptides unique to AMELX and three unique to AMELY, as detailed by IFLScience.
Although DNA is essential for genetic research, it degrades rapidly over time, making paleoproteomics a valuable method for protein analysis since proteins can be preserved longer than DNA. With palaeoproteomics, researchers can now accurately identify the sex of individuals from the species, improving our understanding of their biology and behaviours. The technique has the potential to resolve long-standing debates about sexual dimorphism in early hominins. Determining the sex of prehistoric individuals has traditionally relied on skeletal characteristics, and the incomplete nature of most fossils often makes the task difficult.
Paleoproteomics has been used to study genetic material in creatures that are tens of millions of years old. For example, the remains of a Brachylophosaurus that is 80 million years old were studied using this method. The method pushes the limits of what we can learn from ancient remains, potentially unlocking new insights into human evolution.
Paleoproteomics, a technology developed about thirty years ago, relies on the extraction and analysis of ancient proteins to understand the genetic past of species. Proteins, composed of chains of amino acids, are more robust than DNA and can provide crucial information about the biological characteristics of living beings. Beyond 100,000 years, it becomes almost impossible to extract usable information from DNA.
The study is part of a special issue marking the 100th anniversary of the discovery of the Taung Child, the first Australopithecus fossil ever found. In 1925, Australian anthropologist Raymond Dart first identified Australopithecus africanus as a human relative, a bold and controversial claim at the time.
"I want to expand the application of this technique to other regions and climatic zones in the world," said Madupe. Expanding the use of palaeoproteomics to different environments could reveal how climate and geography influenced human evolution. By comparing preserved proteins across multiple hominin species, scientists could uncover hidden relationships, which could refine our understanding of how our ancestors evolved.
This article was written in collaboration with generative AI company Alchemiq