As a species, we (Homo sapiens) have been around for just 300,000 years - that’s a blink of an eye in terms of geological time.
To put this span of time into perspective, imagine condensing the entirety of Earth’s 4.5-billion-year history into a single, 24-hour day.
- Who first realised the Earth was very, very old?
- How old is life on Earth? Well, it depends on what you mean by 'life'
The first signs of life in this hypothetical day appear at roughly 4 o’clock in the morning, the first dinosaurs at 11 o’clock in the evening, and the first H.sapiens in the last handful of seconds before midnight. In short, H.sapiens are a young species that, in terms of geological time, only appeared very recently.
- What's the difference between humans and apes? And when did we first appear?
- Why don't humans have fur?
However, if we broaden the definition of ‘human’ beyond H.sapiens and include other species within our genus (Homo), as well as species from ancestral (Australopithecus) and closely related (Paranthropus) groups, we can trace our roots a lot further back through time.
Many of these ‘humans’ looked like us, behaved like us, and may have even sounded like us. In them, we see reflections of ourselves and the traits that, over time, we’ve adopted and used to our advantage. You - sat there, reading this article today - may be the end-product of thousands of years of evolution, but you’re no more special than these prehistoric peoples…
The human species that lived before us
Australopithecus afarensis
Before humans became ‘humans’, they were australopithecines. This group includes a number of different species, all of whom look vaguely human-like but different enough that you’d be able to pick them out from a line up of people today.
The most well-known member of this group, Australopithecus afarensis, lived from 3.9 to 2.9 million years ago in East Africa, alongside a number of other australopithecines.
In 1974, a team of researchers discovered an incredibly well-preserved A.afarensis in Hadar, Ethiopia. They named the specimen ‘Lucy’ after the 1967 Beatles song Lucy in the Sky With Diamonds, which was playing on a tape recorder the night of their discovery. Lucy is roughly 40% complete and therefore one of the most important fossil hominins ever found - it’s Lucy who provided the crucial evidence that our ancestors walked upright before they evolved large brains.
A.afarensis possessed both chimp-like and human-like traits. Their skulls looked more like those of chimps and their brains were similarly sized. They also had comparatively long arms - adaptations for climbing - and powerful jaws with enlarged molars that would have been used for grinding up tough plants, such as sedges and grasses. They ate leaves and fruits too, just like today’s chimpanzees.
However, the spines, pelvises, and knees of A.afarensis were a lot more human-like and are thought to have supported a bipedal lifestyle. They’d have still spent a lot of time in trees, but they’d have also walked upright on the forest floor in search of food.
It’s thought our lineage, Homo, emerged from a species of Australopithecus, perhaps A.afarensis or a later species such as A.africanus.
Homo habilis
It’s widely agreed that the ‘human’ branch of the ape family tree began 2.3 million years ago in East and South Africa with Homo habilis.
This diminutive hominid looks more like an Australopithecus than a human alive today; measuring around 1.3m tall (4ft 3in), H.habilis was covered head to toe in hair and had long arms that stretched past its knees. However, it had a flat face, reduced jaw muscles, and smaller teeth - signs that it’s a distinct species and one with a slightly different diet.
H.habilis could also use and manufacture stone tools - a hallmark of species within the Homogenus. It’s likely Australopithecus could do the same, but to date no tools have been found in direct association with any Australopithecus remains. H.habilis, on the other hand, are well-known for making ‘Oldowan’ tools - primitive tools that are, essentially, sharpened rocks.
These tools opened up a world of possibilities for H.habilis, particularly when it came to food. Equipped with choppers, scrapers, and smashers, they were able to properly butcher scavenged animals and get at the most nutritious, energy-rich cuts of meat and bone marrow. This is thought to have fueled their growing brains and set them on a path towards high intelligence.
That said, the brains of H.habilis were only a tad larger than those of Australopithecus (and today’s chimps), so they wouldn’t exactly have made the best prehistoric pub quiz team.
Like Australopithecus, they’d have also spent a lot of their time hiding in the tree canopy. While they could walk upright, they were still prey for lots of different predators, such as crocodiles, leopards, and other big cats.
Paranthropus
Nicknamed the ‘human cow’, Paranthropus is a plant-loving biped that belongs to the australopithecines - a group of early, human-like hominins that includes Australopithecus. The validity of Paranthropus is debated and it’s often considered a synonym of Australopithecus, but they do possess several distinctive traits.
Paranthropus’ members - P.robustus, P.boisei, and P.aethiopicus - are characterised by their large and robust skulls that sport a prominent, gorilla-like sagittal crest along the midline. This crest anchored huge jaw muscles that allowed Paranthropus to chew through tough and fibrous plant material.
Despite having large heads, the bodies of Paranthropus were relatively small and similar in size to those of H.habilis and other australopithecines.
P.robustus was likely an omnivore, but P.boisei is thought to have been almost exclusively herbivorous. This species had giant molars capped with a thick layer of enamel designed to resist the gritty particles that cover plants. It’s suggested P.boisei had a particular taste for nutrient-rich tubers, as these are known to thrive in the wet woodlands it’s thought to have lived in.
As a group, Paranthropus lived from 2.9 to 1.2 million years ago, overlapping with several species of humans. Some suggest Paranthropus is a sister group to Homo, having both evolved from Australopithecus, although this is debated.
While they may be a distinct group that lived very differently to early humans, it’s thought our ancestors were very close with Paranthropus. In fact, a 2017 study found evidence to suggest that Paranthropus gave our ancestors genital herpes (HSV2), serving as the ‘middle man’ that transmitted the virus from ancestral chimpanzees to early humans.
Ardipithecus ramidus
It’s generally agreed that the genus Homo emerged from Australopithecus, but where the earlier australopithecine, Ardipithecus, falls on the ape family tree isn’t quite as settled. There are two known species of Ardipithecus - A.kadabba and A.ramidus - and it’s the latter, younger species that has left us the most fossils to study.
A relatively complete A.ramidus skeleton was discovered in the Afar Region of northern Ethiopia in 1994 and later described in 2009. The specimen was nicknamed ‘Ardi’, dated to roughly 4 million years ago, and comprised teeth and bones from the skull, pelvis, hands, and feet of what researchers think was an adult female that weighed ~50kg. Interestingly, Ardi was found just 74km away from the site where the 3-million-year-old A.afarensis Lucy was found, highlighting just how important this area of East Africa was for human evolution.
When pieced back together, the bones of Ardi paint a startling picture. This early hominin walked on two legs, like us, but she also possessed features that were more chimp-like, such as opposable toes and long arms.
Based on these features, researchers have suggested A.ramidus (and likely A.kadabba) was a facultative biped: walking upright when moving on the ground, but crouching down and walking on all fours when moving through trees. Just how long A.ramidus spent walking on two legs is questionable - some think they may have walked rather clumsily and only been able to run for short periods.
Like today’s chimps and other extinct australopithecines, Ardipithecus were omnivores, though patterns of wear on their teeth suggest they mostly avoided abrasive plants, such as leaves and tubers, and instead dined on fruits and insects.
Sahelanthropus tchadensis
This 7-million-year-old hominid is by far the oldest species on this list and may stretch the definition of what it means to be ‘human’, but falling somewhere between chimpanzees and humans on the ape family tree it can certainly be considered a long-lost relative.
In 2001, a team of researchers working in the Djurab Desert of northern Chad discovered a nearly complete but heavily weathered skull. This skull provided the team with enough taxonomic information for them to erect a new genus and type species: Sahelanthropus tchadensis.
Interestingly, this skull was found on loose sediments at the surface and showed signs of having been exposed to the elements for some time, such as an iron-rich ‘crust’. This may suggest the specimen - known as ‘Toumaï’ - was purposefully buried in a grave; not by other S.tchadensis, but by nomadic humans who stumbled across the remains millions of years later. The remains may have even been reburied again in the 11th century by Muslims who reorientated them towards Mecca after they were re-exposed.
The skull of S.tchadensis is relatively small and similar in size to that of a chimp’s. The teeth, brow ridges, and facial structure are also different from those seen in later human species. However, the skull is quite human-like, so it’s no surprise that it may have been misidentified by historic peoples who lived long before Charles Darwin and the idea of evolution.
Alongside Toumaï’s skull, several limb bones were also found. A series of recent studies have debated whether or not these bones suggest S.tchadensis walked on two legs. Some believe they do, while others argue that S.tchadensis probably walked on its knuckles like gorillas and chimps do today.
S.tchadensis probably lived a lot like gorillas and chimps, inhabiting forests, forest margins and grasslands and subsisting on a largely plant-based diet.