This is an extract from Our Human Story, our newsletter about the revolution in archaeology. Sign up to receive it in your inbox every month.
Whenever we think about the process of evolution, there’s a risk of falling into the trap of telling stories. Human minds are prone to interpret the world in terms of stories: it’s just one of our biases, along with the one that causes us to see faces in clouds and on pieces of toast. So we always have to be careful not to let our narrative instincts run away with us.
We must remember than when thinking about Australopithecus. First, let’s divide all of human evolution into four phases:
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- 7 million to 4 million years ago: Nebulous
- 4 million to 2 million years ago: Mostly Australopithecus
- 2 million to 0.04 million years ago: Various Homo
- 0.3 million to present: Homo sapiens
In this simplified scheme, Australopithecus is phase two. They came after the early ape-like hominins Sahelanthropus, Orrorin and Ardipithecus – and they came (mostly) before the genus Homo, to which we belong.
Because we see this chronological sequence, it’s tempting to tell a story. Sahelanthropus (7 million years ago) evolves into Orrorin (6 million years ago), and so on into the group of hominins known as Australopithecus – which then evolves into the earliest Homo. In this scenario, Australopithecus are our direct ancestors.
That doesn’t mean that any specific Australopithecus individual is our ancestor. Several species have been identified, and maybe only one of them was ancestral to Homo. Nevertheless, if we could draw our family tree, there would be a lot of Australopithecus around 100,000 generations ago.
However, I want to point out a simple fact: we don’t actually know this. There are reasons to think it’s true and some of them are good, but it is at best an educated guess. How, then, might we demonstrate it?
Extinct ancestors
One hundred years ago, on 7 February 1925, was published in Nature. Palaeoanthropologist Raymond Dart had obtained the specimen known as the Taung Child the previous November – something I mentioned in November’s Our Human Story – and swiftly got his results out.
The main point Dart made was that , not in Eurasia as was widely assumed by scientists at the time. Finding the remains of an Australopithecus in South Africa was strong evidence for this, although it took a long time for Dart’s findings to be accepted. Today, researchers are near-unanimous that the origins of our species lie in Africa.
Australopithecus were clearly an important part of the story. For one thing, they were around for over 2 million years, nearly ten times as long as our species has managed. The oldest known species, Australopithecus anamensis, was living in what’s now Kenya . The most recent one, Australopithecus sediba, was in South Africa . If we assume that the story of human evolution spans 7 million years, then Australopithecus makes up almost a third of it.
This is the first reason why researchers tend to think Australopithecus, or at least some of them, were our ancestors. There just aren’t many other good candidates.
Here’s a more detailed timeline of human evolution, highlighting the seven hominin groups, or genera, that have been identified so far:
- Sahelanthropus: 7 million years ago
- Orrorin: 6 million years ago
- Ardipithecus: 5.6-4.4 million years ago
- Australopithecus: 4.2-2 million years ago
- : 3.5-3.2 million years ago
- Paranthropus: 2.8-1.4 million years ago
- Homo: 2.4-0 million years ago
If we want to identify the direct ancestors of Homo, then on this basis there are three candidates: Australopithecus, Kenyanthropus and Paranthropus. They are all known to have existed before and around the time Homo emerged.
Kenyanthropus are only known from a handful of fossils, most notably a badly squashed skull. This means we know little about them, and plenty of researchers dispute the claim that they’re a separate genus.
We know more about Paranthropus, but what that knowledge tells us is that, if Homo evolved from them, there must have been a rapid spurt of evolution involved. Paranthropus were small-brained for such recent hominins, and seem to have been heavily dependent on grasses and other tough vegetation for food.
In contrast, Australopithecus had larger brains and more omnivorous diets. They had other human-like traits too. A study published in October looked at patterns of wear on their hand bones and found . Apes don’t show this pattern of wear, but hominins that make and use stone tools do.
Nevertheless, even now, there are researchers arguing that Australopithecus aren’t our ancestors.
Ancestors – but whose?
In 2023, researchers led by at Ghent University in Belgium published a study with the brisk title: “”.
The argument is essentially that it’s a mistake to believe that Australopithecus is a neat halfway house between apes and humans. For example, some apes that lived over 5 million years ago appear to have walked upright, at least some of the time. We don’t know what the last common ancestor of apes and humans was like, but it may not have been especially similar to our closest living relatives, the chimpanzees – in particular, it may not have knuckle-walked. Meanwhile, Australopithecus had adaptations to tree-climbing despite being bipedal.
Hence Vaneechoutte and colleagues argue that Australopithecus were actually the ancestors of modern African apes: chimps, bonobos and gorillas. On this view, upright walking evolved in some apes millions of years ago and was preserved in the populations that gave rise to us – whereas Australopithecus and their ape descendants gradually abandoned this behaviour for knuckle-walking and tree-climbing.
I want to emphasise that this is a niche opinion. Most researchers in the area would disagree with it, and I personally find it unconvincing. I’m not raising it to argue that it’s correct.
Instead, I want to highlight that this opinion is only worth considering at all because of three lingering uncertainties.
First, we have no fossils of the ancestors of modern African apes over the past few million years, so we don’t know how chimpanzee evolution played out. If someone wants to argue that chimps evolved from Australopithecus, there isn’t an evidence-based narrative to counter such a claim.
Second, we don’t have a good fossil record of the transition from Australopithecus to Homo. Big-brained Homo pretty much just popped up, seemingly out of nowhere: as yet, we don’t have fossils that are intermediate between the two. Hence the pithy title of a 2016 paper: “”.
And third, we don’t have molecular evidence. Ancient DNA or protein from Australopithecus would clarify their relationships to us and to great apes. Because there’s so much information stored in these molecules, they are often a more reliable guide to evolutionary relationships than bones.
Those first two problems may not be solved anytime soon, purely because fossil hunting involves so much chance. However, molecular data from Australopithecus is on its way.
At the annual meeting of the American Association of Biological Anthropologists in March 2024, researchers led by at the University of Copenhagen in Denmark announced that they had “”. They had extracted protein from a tooth found in Sterkfontein caves in South Africa and concluded that it belonged to a male. The previous year, Madupe and her colleagues also .
°Őłó±đĚýAustralopithecus findings have now been in a special issue of the  about the centenary of the Taung Child. Madupe and her colleagues say they cannot use the data to place A. africanus in a hominin family tree, because they only collected a minimal set of proteins. However, they’re equally clear that they see this as a preliminary study, and plan to do much more.
It’s taken a century, but soon we might be able to confidently fit Australopithecus into the human story.
