Our Ancient Ancestors: the Lineage of the Human Race (#156)

Today’s episode is going back to ancient times, and I’m not talking about the Ancient Greeks or Romans – I’m talking before our human race existed as we know it. I’m going to be talking about the origins of the human race, and some of the races that would have been our distant ancestors.

As stated by the Natural History Museum, the story of human evolution is not one of neat, linear progression with a concrete beginning and end. Instead, it is a tale of a family tree whose complex and bushy branches stretch over many millennia and continents. It features a changing cast of ancient hominid relatives, evolutionary dead-ends and many unknowns, and the story is full of adaptation, survival and extinction.

By piecing together fossil traces, scientists over time are revealing what our ancient relatives were like, how they were related and how they adapted to life in different landscapes and challenging climates.

Modern human beings, or Homo sapiens, emerged relatively recently, only about 315,000 to 150,000 years ago. 150,000 sounds big, but when you think about the fact that ancestors of the human race have been around for millions of years, 150,000 is tiny in comparison. Over all that time, the human lineage has survived a long and arduous journey, and our genetic path has followed numerous twists and turns.

So let’s have a look at some of the races that make up our human lineage! (And, as usual, apologies for any awful pronunciations of words that I’m going to have to attempt.)

Ardipithicus

First up is Ard-ip-ith-icus, the earliest known genus of the human lineage and the likely ancestor of Austra-lo-pith-ecus, a group closely related to and often considered ancestral to modern human beings. Ardipithecus lived between 5.8 million and 4.4 million years ago. The genus is known largely from the discovery of a partial skeleton that was named Ardi. Ardi’s skeleton was notable in that the braincase was similar in size to that of a chimpanzee, and it has long arms and fingers and opposable toes, but it did not have large sharpened canine teeth like those seen in apes. Ardi’s pelvis and foot had more in common with later members of the human lineage than those of the apes, and researchers think that Ardi was capable of walking, even though she likely spent much of her time in the trees.

Australopithecus

So now we have one I already mentioned, and that’s the Australopithecus. Appearing in East Africa approximately 4.4 million years ago, australopithecus had a combination of humanlike and apelike traits — in fact, these may have been the first primates to get around mainly by walking upright, a big step in the early evolution of humans. (However, bipedalism — which basically means moving around using only two legs, for example, four-legged animals using their back legs to get around — was likely to have appeared much earlier, in species that lived up to 7 million years ago, compared to 4.4 million for the Australopithecus.) 

So, these guys had long arms and curved fingers that enabled them to move easily among the trees, and their legs were shorter than those of contemporary humans. They were unable to talk but had brains slightly larger than a chimpanzee’s. In 1974, palaeontologist Donald C. Johanson discovered the skeleton of a young Australopithecus in Ethiopia. He named her Lucy, and she remains one of the most famous fossils in the world.

Homo habilis

Some of the most impressive evidence of human evolution has come from Olduvai Gorge in Tanzania. It was there in the early 1960s that palaeontologist Louis Leakey and his team discovered the remains of an early bipedal hominid species called Homo habilis that, for a period, lived alongside the australopithecus. What made this species unique was their larger brain, the reduction in the heavy brow ridges, and other anatomical changes to the skull that differed hugely from those characteristic of the australopithecus. For several decades, Homo habilis was thought to be the oldest toolmaker, a perception which gave it its Latin name which translates as “handyman”. However, tools discovered at Kenya’s Lake Turkana in 2013 were shown to have predated the emergence of homo habilis by almost 400,000 years.

Homo erectus

Now we’re definitely starting to see the development of very human-like characteristics and skills. Homo erectus were early hominids that lived on the ground, walked upright, created tools to aid in hunting, and lived in groups or bands. It was the first of our relatives to have human-like body proportions, with shorter arms and longer legs relative to its torso. It was also the first known hominin to migrate out of Africa, and possibly the first to use fire to cook food. In terms of species survival, Homo erectus is a huge success story. Fossil evidence for Homo erectus stretches over more than 1.5 million years, making it by far the longest surviving of all our human relatives.

Homo erectus is what researchers refer to as a chronospecies, meaning it changes through time. According to some scientists, Homo ergaster could have been the earlier phase of the species, which lived primarily in Africa; the more-evolved Homo erectus lived in Eurasia. Others argue that Homo ergaster may have belonged to a separate lineage. Homo erectus moved out of Africa approximately 1.8 million years ago.

Precisely when - and why - Homo erectus disappeared is unclear, but it appears to have survived in parts of Indonesia until at least 250,000 years ago.

Homo heidelbergensis

Between the time Homo erectus left Africa and the appearance of Homo sapiens, a unique branch of the Homo genus, called Homo heidelbergensis, appeared in Europe, northwestern Africa, and possibly Asia. Named after the location in Germany where the first remains were found, the species lived from 600,000 to 200,000 years ago. We now see another human skill emerge: they were unique in that they built shelters to protect themselves from the cold weather and used spears to hunt large game. While they certainly predated the Neanderthals, some scientists argue that members of Homo heidelbergensis became the ancestors of the Neanderthals, but this is still a matter of debate.

Homo neanderthalensis

So, that brings us to the Neanderthals, or Homo neanderthalensis. We know more facts about Neanderthals than any other extinct humans. Many thousands of their artefacts and fossils have been found, including several nearly complete skeletons. We also know about their genetic make-up, as several Neanderthal genomes have now been reconstructed from ancient DNA obtained from their fossils.

Neanderthals were humans like us, but they were a distinct species called Homo neanderthalensis. Together with an Asian people known as Denisovans (who were named after the cave in Siberia where a few small bones provided conclusive evidence of their lineage), Neanderthals are our closest ancient human relatives. Scientific evidence suggests our two species shared a common ancestor. Dating issues and fossil anatomy mean that scientists are currently uncertain whether the last common ancestor of Neanderthals and modern humans was Homo heidelbergensis, or another species.

Current evidence from both fossils and DNA suggests that Neanderthal and modern human lineages separated at least 500,000 years ago. Neanderthals lived alongside early modern humans for at least part of their existence. We now know that some encounters between humans and Neandethals were more intimate in nature — as some of us have inherited around 2% Neanderthal DNA.

The Neanderthals have a long evolutionary history. The earliest known examples of Neanderthal-like fossils are around 430,000 years old. The best-known Neanderthals lived between about 130,000 and 40,000 years ago, after which all physical evidence of them vanishes.

Neanderthals evolved in Europe and Asia while modern humans - our species, Homo sapiens - were evolving in Africa. The species ranged widely in Eurasia, from Portugal and Wales in the west across to the Altai Mountains of Siberia in the east. Neanderthal populations were adaptable, living in cold environments in England and Siberia about 60,000 years ago, and in warm temperate woodlands in Spain and Italy about 120,000 years ago.

They were adept at making fire, creating stone and wooden tools as evidenced by excavated objects such as spears and flint handaxes, and fashioning clothes from animal skins. They also made jewellery! Some of this jewellery was apparently fashioned from eagle talons. The oldest examples are about 130,000 years old. Pierced animal teeth and worked ivory have been found at Neanderthal sites in places like France. It’s also likely that they used natural pigment as coloured dye.

With squat, brawny bodies and broad facial features, the Neanderthals developed to survive the harsh climates in which they lived. Despite their reputation as being primitive 'cavemen', Neanderthals were actually very intelligent and accomplished humans. These were no 'ape-men'. So it's actually quite unfair to them that the word Neanderthal is used as an insult today.

The extinction of Neanderthals is a well-known fact, but why did this species disappear after having survived for more than 350,000 years? This still remains a bit of a mystery. One view is that we are the reason. Early modern humans started to arrive in Europe more than 40,000 years ago. Perhaps Neanderthals were unable to cope with competition for resources from incoming groups of Homo sapiens. Science has shown that their numbers and diversity were relatively low in their last 20,000 years of existence. The sometimes extreme fluctuating climate, and rapid climate change, unfortunately didn’t do them any favours either, meaning only the strongest could survive.

Homo floresiensis

One of the more recent discoveries was in 2003, when researchers uncovered the remains of a prehistoric woman on Flores Island near Java. She was extremely short, with a brain about a third the size of a contemporary human’s. Because of her small stature, she was nicknamed “the hobbit,” but her species is known scientifically as Homo floresiensis. At just over one metre tall, this species might have been slight in stature, but it has attracted lengthy debate due to its mysterious origins.

Exactly when Homo floresiensis appeared on Flores is unclear, but the oldest known remains are at least 100,000 years old, while some stone tools attributed to Homo floresiensis are as much as 190,000 years old.

When the species was first discovered, the team dated the fossil skeleton to less than 20,000 years old. If the species was present on Flores that recently, it would mean that a primitive hominin had survived on the island well into the era of modern humans. However, the age of the skeleton was later revised to about 60,000 years old, with an estimated last appearance of Homo floresiensis about 50,000 years ago, based on stone tools.

So far, no modern human remains have been found in the region as early as 50,000 years ago, so this revised date might mean Homo floresiensis was physically extinct before the appearance of modern humans in the region.

Homo naledi

Finally, one of the most recent discoveries of a human relative is Homo naledi, fossils of which were only discovered in 2013! 10 years ago, a bounty of fossils was discovered deep in a South African cave. They were identified as a new human species with a surprising combination of features. The discovery of hundreds of Homo naledi fossils was the largest such find ever made on the African continent. The fossils display a unique mix of modern and archaic traits and are shaking up our understanding of the origins and diversity of our human lineage.

It’s believed this species lived 300,000 years ago, and had a small head with a very projecting face, a relatively slender body but with wide hips, and human-like feet and hands, but long curved fingers. According to scientists, some of Homo naledi's features, such as its hands, wrists and feet, are very similar to those of modern humans and Neanderthals – but other characteristics are much more primitive. The species’ small brain and the shape of its upper body are more similar to the pre-human australopithecus, and the very early human species Homo habilis.

Their young age means Homo naledi was living on the African continent with a number of other bigger-brained humans, including our own species Homo sapiens.

One of the biggest mysteries of this species is how their bones ended up deep in the caves where they were discovered. There is no evidence to suggest humans ever lived so deep in the caves. The authors of the first Homo naledi studies rejected scenarios such as water carrying the bones there or predators dragging them there. Instead, they favour the idea that other members of the species disposed of bodies in the caves intentionally and repeatedly.

However, human evolution expert Prof Stringer isn't convinced. He said, “'Many experts, including me, consider such complex behaviour unlikely for a creature with a brain size close to that of a gorilla, particularly when a requirement for the controlled use of fire, for lighting, probably has to be added in. I think alternatively it's possible that, now and again, individuals sought refuge deep in the cave to escape from predators or other humans. Without light and climbing equipment, once deep in the cave, there may have been no way back. Over hundreds or thousands of years, this behaviour could have led to an accumulation of bodies deep in the cave.”

Conclusion

In recent years, the timeline of human evolution has shifted from being that of a simple tree as new species evolved and branched off, to something of a thicket. More and more ancient human species have been found to survive to within the last 100,000 years, suggesting that in some places, at least, there may have been significant overlap between our own ancestors and these ancient species.

Southeast Asia, in particular, was once home to numerous species of human. In an early migration out of Africa, the incredibly successful Homo erectus made it to China and Indonesia, while it is thought that the more enigmatic Denisovans may even have reached the vicinity of Papua New Guinea.

So who knows what is still out there to be discovered, and what will happen to the human race in the distant future as it continues to evolve!