A scientist has proposed a radical rethink of the human family tree

Human evolution is often depicted as a linear sequence: ancient ape-like ancestors, followed by the Australopithecines, the first members of the genus Homo, and, finally, modern humans.

However, new fossil discoveries paint a far more complex picture.

Different species of hominins co-existed, combining features previously thought to be characteristic of different genera, and may have exhibited more complex behaviour than scientists had assumed.

This is precisely why researcher Ian Towle of Monash University believes that the traditional division into Australopithecus, Paranthropus and Homo no longer accurately reflects the actual evolutionary relationships.

Details

Currently, the genus Homo includes modern humans and a number of extinct species, including Homo erectus, Homo habilis and Neanderthals.

Towle proposes significantly expanding this group to include hominins that lived over the last approximately 4–5 million years.

This would include species that are currently classified as Australopithecus and Paranthropus.

This would entail a major overhaul of the conventional classification of human evolution.

For example, the famous Lucy, who lived some 3.2 million years ago, is currently known as Australopithecus afarensis. Under the proposed system, her species would have to be classified within the expanded genus Homo.

But this would not mean that Lucy was a ‘modern human’. Homo, in this context, is the scientific name of the genus, not a definition of intelligence or human behaviour.

One of the problems with the traditional classification has been the characteristics previously used to define the genus Homo.

For a long time, these included a relatively large brain, the manufacture of complex tools, anatomical features and sophisticated behaviour.

However, new discoveries have gradually blurred these boundaries.

There are known species within the genus Homo with a small brain volume. At the same time, archaeological evidence suggests that tool-making and certain complex forms of behaviour may also have existed among hominins not classified as Homo.

According to the author of the paper, it is becoming increasingly difficult to constantly revise the definition of the genus to accommodate every new discovery.

Instead, he proposes expanding the genus Homo itself.

The proposal regarding Paranthropus appears particularly radical.

Paranthropus lived in Africa approximately 2.7–1.2 million years ago and were characterised by massive jaws, large teeth and a powerful masticatory apparatus.

They are usually regarded as a separate lateral branch of hominin evolution, rather than as direct ancestors of modern humans.

Nevertheless, Towle believes that the existing generic boundaries between them, the australopithecines and Homo may not be sufficiently reliable from the perspective of modern evolutionary systematics.

The main argument is that scientific classification should group a common ancestor and all its descendants into a single evolutionary group, whereas traditional nomenclature does not always allow for this.

This is a key limitation of the study.

The author proposes changing the classification, but the scientific community has not yet adopted the new system.

The names Australopithecus and Paranthropus continue to be used, and the question of exactly which species should be grouped into a single genus remains a subject of scientific debate.

Furthermore, expanding the genus Homo would result in an extremely diverse group — ranging from the comparatively small australopithecines to modern humans.

Therefore, other experts may consider maintaining several separate genera to be more informative.

Why this matters

The dispute may seem to be merely a matter of nomenclature, but in reality it concerns how scientists conceptualise the very process of human evolution.

If ancient hominins constantly have to be reclassified between genera as new discoveries are made, perhaps the problem lies not only in the incomplete fossil record, but also in the classification system itself.

Towle’s proposal illustrates just how far modern palaeoanthropology has moved away from the old picture of linear evolution.

Today, the human family tree looks more like a dense bush with numerous branches that existed simultaneously, many of which combined unexpected anatomical and behavioural traits.

This is precisely why the question of where the genus Homo begins has once again become an open one.

Source

Study: Clades, grades, and the genus problem: A case for revising hominin taxonomy.

Journal: American Journal of Biological Anthropology, 2026.