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Before the first fossils of our ancestors were unearthed, anatomists studied the differences between humans and our closest living relatives, the great apes, for clues as to our origins. Since then, the study of ancient human remains has given us a wealth of information about how humans evolved. As Professor Alice Roberts unearths our distant past on BBC Two’s Prehistoric Autopsy this autumn, we explore the skeletons of three early human relatives to reconstruct how we conquered the planet.
Until the 1930s, scientists believed that our bigger brain was the key characteristic that drove human evolution over our ape relatives. But over the last few decades, it’s become clear that this early theory is wrong. Fossils of hominins (the evolutionary branch that includes humans and our extinct ancestors) are revealing more about the major steps that led to modern humans. The earliest hominin fossils – dating back six million years – show, for instance, that our ancestors walked on two legs long before their brains became bigger.
Certain physical features have made Homo sapiens the masters of the planet, enabling us to develop language, use tools and create art. And by examining every aspect of the body, from arms and ankles to feet and teeth, palaeoanthropologists are uncovering the anatomical innovations that have ultimately made us who we are.
In this article we examine the skeletal remains of the hominin species of Australopithecus afarensis, Homo erectus and Homo neanderthalensis, marking three key areas of human evolution.
Over 400 fossils of Australopithecus afarensis have been found across East Africa, but one partial skeleton is especially well known. When this female specimen was discovered at Hadar in Ethiopia by palaeoanthropologist Donald Johanson in 1974, his team celebrated by repeatedly playing the Beatles song Lucy In The Sky With Diamonds. And so the fossil was named Lucy.
‘Lucy’s species’, Australopithecus afarensis, lived from 3.9 to 2.9 million years ago and shared much in common with modern apes. Curved fingers and toes, more mobile shoulders and relatively longer arms indicate that they would have relied on trees to build nests, escape from predators and collect fruit and nuts for food. Their brains were only a third the size of our own and wouldn’t have taken as much time to grow. Babies developed as fast as apes do, which would have meant less learning before they reached adulthood, compared to modern humans. The males were also much larger than females and they probably lived in small family groups.
Despite having ape-like characteristics, Australopithecus afarensis is considered an early hominin. This is based on some distinctly human-like evolutionary changes, including smaller canine teeth and a hole in the skull where the spinal cord passes through to the body underneath, which shows that the head was carried above the body and not in front, as in apes.
Most notably, there are several changes to the skeleton for walking on two legs: the hips are wide, short and bowl-shaped to carry the weight of the body, as in humans, while the legs angle inwards to bring the knees and feet together. These adaptations for bipedal walking enabled these early hominins to cover larger distances between food sources – with a range covering East Africa – and allowed our ancestors to survive the changing environment with which they were faced, from rainforests to woodlands.
During human evolution, various hominin species arose but soon went extinct. Homo erectus was one of the exceptions: a long-lived and very successful species that walked the Earth 1.9 million to 200,000 years ago.
The most famous specimen is known as ‘Turkana Boy’, who was discovered in 1984 by fossil hunter Kamoya Kimeu at Nariokotome, Kenya. This almost complete skeleton provided the first definitive proof that the post-cranial skeleton – everything below the skull – was essentially human over a million years before the brain reached human size. Unlike apes, they stood up straight, hence their nickname: ‘upright man’.
Their anatomy, along with tools found with fossils, show that Homo erectus was the first true hunter-gatherer. The body is adapted to long-distance walking and running. Biologist Dennis Bramble and anthropologist Dan Lieberman suggest these adaptations enabled them to hunt large mammals.
Without projectile weapons such as bows and arrows, Homo erectus may have been a persistence hunter that chased and tracked large animals to exhaustion, then killed them with fairly simple tools. Hunting would have provided meat, a high-energy food necessary to fuel bigger brains.
Although Homo erectus still grew up faster than humans today and therefore learned less before they reached maturity, they became a very successful species because they lived in family groups, co-operated, and may even have had a rudimentary form of language, allowing them to communicate. There’s also fossil evidence that they cared for the old and weak.
All their abilities – being able to hunt, gather and use tools and fire – made it possible to survive in a range of environments. This enabled Homo erectus to not only spread across the whole of Africa, but to become the first human ancestor known to leave the continent and populate western and eastern Asia, all the way to Indonesia.
Although fossils of Homo neanderthalensis were first discovered in Belgium in 1829, they weren’t recognised as an early human ancestor until a partial skeleton was found in Neanderthal, Germany, in 1856. Hundreds of fossils have since been found, making them our best understood relatives.
Neanderthals lived in the cold climate of Europe and Asia around 200,000 to 30,000 years ago, and they were well adapted to life in their harsh environment: short, stocky bodies and short limbs helped to retain heat in the core while also reducing surface area where heat could be lost. Their noses were huge and probably served to heat and humidify the cold, dry air before it passed down to the lungs.
It’s possible Neanderthals were as intelligent as early Homo sapiens because their brains were as large, and sometimes larger, than ours. But their skulls still had a primitive large brow ridge and were elongated and flattened in shape.
The way of life for Neanderthals was very similar to that of early modern humans: they lived in caves and rock shelters, and probably wore clothing. Neanderthals were also skilled at making and using tools to hunt large animals like mammoths, and they gathered fruit, legumes and nuts. In terms of culture, they almost certainly used language and even buried their dead – a sophisticated symbolic behaviour not seen in other extinct hominins.
Comparing Neanderthal DNA to that from modern humans has provided fascinating insights. For example, it’s clear that when humans left Africa and reached Western Asia, they met and interbred with Neanderthals – people of non-African heritage carry up to three per cent Neanderthal DNA.
Although Neanderthals thrived in Ice Age Europe, they were probably out-competed by the newly-arriving modern humans, and went extinct within about 10,000 years of humans arriving in Europe.
Dr Isabelle De Groote is a palaeoanthropologist at the Natural History Museum and was a consultant on the BBC series Prehistoric Autopsy.
The full version of this article appeared in the September 2012 issue of Focus.