Dr. Ian Towle, a researcher with the Biomedicine Discovery Institute at Monash University, proposes folding nearly 5 million years of hominin fossils into the genus Homo, arguing that traits once used to separate species — big brains, tool use — no longer hold up.
Paranthropus boisei. Image credit: © Roman Yevseyev.
“Recent discoveries are eroding the usefulness and accuracy of current classification, including the current species in our own genus Homo, but also in Australopithecus and Paranthropus, who all 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 our traditional taxonomy still accurately reflects human evolution.”
“These groups do not necessarily represent distinct evolutionary branches, or clades, and differences in behavior and ecology once used to distinguish them have also become increasingly difficult to maintain.”
“I propose expanding Homo to include these other groups to provide a more accurate and stable way to represent the complex evolutionary relationships revealed by the growing fossil record.”
Dr. Towle argues that the current three-genus system taught in textbooks and museums no longer reflects what the fossil evidence actually shows.
He contends that Australopithecus in particular functions as a taxonomic wastebasket, a grouping repeatedly shown by phylogenetic studies to be non-monophyletic, meaning it doesn’t consist of a single ancestor and all its descendants, the standard modern biology uses to define a valid group.
He also traces how traits once considered defining features of Homo, such as brain size or tool use, have been undermined by discoveries like Homo naledi and Homo floresiensis, both small-brained species that nonetheless get grouped with humans.
Meanwhile, species like Australopithecus garhi have shown tooth sizes larger than even the most robust Paranthropus specimens, further blurring the boundaries between genera.
To bolster the case, Dr. Towle draws comparisons to living primates, particularly baboons and their relatives, where genetic studies have revealed extensive interbreeding between closely related genera.
He suggests that hominin genera defined too narrowly in time — within the last few million years — are especially prone to this kind of instability, since gene flow between closely related lineages tends to persist for a few million years after initial divergence.
Under his proposal, the expanded Homo genus would stretch back roughly 4 to 5 million years, anchored at the branching point of Australopithecus anamensis, a node he describes as one of the rare areas of consensus in paleoanthropology.
The tribe Hominini would be redefined as the pan-Homo clade (encompassing both chimpanzees and humans’ lineage), with a new subtribe, Hominina, used specifically for the human branch.
Collapsing three genera into one would erase distinctions that many researchers view as biologically meaningful, particularly between Homo and Paranthropus, which followed markedly different evolutionary and dietary paths.
“Reclassifying Australopithecus and Paranthropus species under the category of Homo will provide a more coherent understanding of our evolutionary history and avoid continual redefinition as we discover new fossils and learn more about our ancestors,” Dr. Towle said.
“The more we learn about our ancestors and close fossil relatives, the more we realise how complex and non-linear our family tree is.”
“Expanding the Homo genus to also include species of Australopithecus and Paranthropus will allow us to account for differences without regularly reclassifying particular groups.”
The paper appears this week in the American Journal of Biological Anthropology.
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Ian Towle. 2026. Clades, Grades, and the Genus Problem: A Case for Revising Hominin Taxonomy. American Journal of Biological Anthropology 190 (4): e70344; doi: 10.1002/ajpa.70344
