A protein analysis suggests the supposed cannibal species Homo antecessor was distantly related to humans and Neanderthals.
To reach these results, the researchers used a method called paleoproteomics — literally, the study of ancient proteins. Using mass spectrometry, which displays the masses of all the molecules in a sample, scientists can identify the specific proteins in a given fossil. Our cells build proteins according to instructions contained in our DNA, with three nucleotides, or letters, in a string of DNA coding for a specific amino acid. Strings of amino acids form a protein. So, the amino acid chains that form each person’s unique protein sequence reveal the patterns of nucleotides that form that person’s genetic code, lead study author Frido Welker, a molecular anthropologist at the University of Copenhagen
Studying ancient proteins therefore opens a window into our genetic past in a way that DNA analysis cannot. DNA degrades relatively quickly, becoming unreadable within several hundred thousand years. To date, the oldest human DNA ever sequenced was about 430,000 years old (also discovered in Spain), according to a 2016 Nature study. Proteins, meanwhile, can survive in fossils for millions of years. Scientists have previously used similar protein sequencing methods to study the genetic code of a 1.77-million-year-old rhino found in Dmanisi, Georgia, and a 1.9-million-year-old extinct ape in China.
While protein analysis allows researchers to look much further into the past than other genetic-sequencing methods, the findings are still limited by the quality and number of specimens available to study. Because the present research is based only on a single tooth from a single H. antecessor individual, the results provide only a “best guess” as to where the species lands on the human evolutionary tree, the authors wrote. Different types of cells produce many different kinds of proteins, so this enamel proteome is far from a complete genetic profile. More fossil evidence is needed to flesh out these results.
Of course, the quality of those fossil samples matters, too. As part of this study, the researchers also examined a 1.77-million-year-old molar taken from a fossil Homo erectus (an ancient human ancestor that lived 2 million years ago) previously discovered in Georgia; however, the protein sequence was too short and damaged to offer any new insights about the specimen’s DNA. Our human family tree will have to remain, for now, a tangled messy bush.