Dr. Ian Towle, a researcher at the Monash University Institute for Biomedical Discovery, has proposed expanding the genus Homo to include several hominin groups that lived during the past 5 million years, including Australopithecus and Paranthropus. He argues that traits traditionally used to define Homo, such as large brains and tool use, no longer provide clear boundaries between hominin genera.
Paranthropus boisei. Image credit: © Roman Yevseyev.
“Recent discoveries have undermined the usefulness and accuracy of current classifications, including the species currently placed in our own genus, Homo, as well as Australopithecus and Paranthropus. All of these groups lived within the past 5 million years,” Dr. Towle said.
“Discoveries and advances in evolutionary and genetic analysis make this an ideal time to reconsider whether traditional hominin taxonomy accurately reflects the history of human evolution.”
According to Towle, these groups do not necessarily represent distinct evolutionary branches, or clades. The behavioral and ecological differences once used to distinguish the genera are also becoming increasingly difficult to maintain as new fossil evidence emerges.
“We propose expanding Homo to include these other groups, providing a more accurate and stable framework for representing the complex evolutionary relationships revealed by the growing hominin fossil record,” he said.
Dr. Towle argues that the traditional three-genus model taught in textbooks and displayed in museums—Homo, Australopithecus and Paranthropus—may no longer reflect the full complexity of human evolution.
He identifies Australopithecus in particular as a classification “wastebasket taxon”: a broad category that may not represent a single evolutionary lineage. In modern biology, a valid clade is generally expected to include a common ancestor and all of its descendants.
Traditional definitions of Homo have also focused on characteristics such as increased brain size and tool use. However, discoveries of species including Homo naledi and Homo floresiensis have challenged those assumptions. Both species had relatively small brains but are classified within the same genus as modern humans.
Conversely, Australopithecus garhi displayed features, including large teeth, that overlap with traits traditionally associated with Paranthropus. Evidence of early tool production further blurs the boundaries between these hominin genera.
To support his proposal, Towle compares humans and other primates, including baboons and their close relatives. Genetic studies of living primates have revealed extensive interbreeding and gene flow between related genera.
He suggests that gene flow between closely related lineages can continue for millions of years after their initial divergence. As a result, narrowly defined genera, including Homo during the past several million years, may be unstable as new genetic and fossil evidence becomes available.
Under the proposed classification, the genus Homo would extend back approximately 4 to 5 million years, with its origin placed near the branching point associated with Australopithecus anamensis. Towle describes this evolutionary node as one of the few areas of broad agreement within paleoanthropology.
The proposal would also redefine hominins within a broader Homo clade that includes the chimpanzee and human lineages, while recognizing a new subtribe, Hominina, for the human lineage.
However, merging Australopithecus and Paranthropus into Homo would remove distinctions that many researchers consider biologically meaningful. In particular, Homo and Paranthropus appear to have followed markedly different evolutionary, anatomical and dietary pathways.
“Reclassifying Australopithecus and Paranthropus species within Homo would provide a more consistent framework for understanding human evolution. It could also reduce the need for repeated taxonomic changes as new fossils are discovered,” Dr. Towle said.
“The more we learn about our ancestors and fossil relatives, the more we realize how complex and nonlinear the human family tree is.”
“Expanding the genus Homo to include species currently assigned to Australopithecus and Paranthropus would allow researchers to recognize important differences without constantly redefining entire groups.”
The paper was published this week in the American Journal of Biological Anthropology.
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Ian Towle. 2026. The issue of clades, grades, and genera: The case for revising hominin taxonomy. American Journal of Biological Anthropology 190 (4): e70344; doi: 10.1002/ajpa.70344
Source: www.sci.news