About 2 to 3 million years ago there was a big freeze that killed the majority of animal life on land and sea. Africa was the region least affected by the Ice Age and life continued to flourish there. As wet, warm grasslands spread across the continent, these habitats created the perfect conditions for the evolution of the great apes: gorillas, chimpanzees and later the hominins or hominids (creatures between ape and human), from which we modern humans finally appeared. These primates gingerly came down from the trees to inhabit the ground and placed their safety in their wits rather than their strength.

It was the Victorian biologist Charles Darwin who first made the observation, in his 1871 book The Descent of Man, that since the African gorilla and chimpanzee are most like us in terms of their anatomy, and because they only existed in Africa, then humans must have originated there. Although Darwin's reasoning may not meet today's scientific standards, he had advanced a ground-breaking theory that creationists and many religious conservatives found abhorrent.

Gorillas are now only found in a few places in Africa, mainly in the Great Lakes region. More than a third of the 1,000 surviving mountain gorillas live under protection in the wild forests of the Virunga National Park. The mountains, a chain of volcanoes, span parts of Rwanda, the Democratic Republic of the Congo (DRC) and Uganda. I set off to see these endangered creatures in northern Rwanda, a mission that involved a long hike starting at dawn, through masses of thick vegetation glistening with morning dew. My exertions paid off when I eventually spotted the gorillas through the foliage. A couple of adult gorillas, including one majestic silverback, lay indolently on the ground—seemingly revelling in the early morning sunshine, while a pair of young gorillas tumbled down from a mound and played together on the muddy earth. It was remarkable to see how similar they are to humans. They live in family groups and their movements, antics and expressions are so like ours. In fact, data shows that humans and gorillas differ in only 1.75 per cent of their DNA, far less than previously assumed. (Chimpanzees—our closest relatives—differ only 1.37 per cent from our genomes.)

Once Charles Darwin had advanced his theory that humans originated in Africa, other scientists began to try to piece together the evolutionary chain from gorillas and chimpanzees to humans by studying extinct species of hominins and looking at bipedalism in particular. Bipedalism, which occurred about 6 million years ago, meant a primate's hands could remain free. About 3 million years later, this led to hominins being able to use their intelligence to make tools or hunt with weapons, assisted by their ability to rotate the wrist, a feature unique to apes and humans. Habitual bipedalism, the ability to walk permanently on two legs, is a defining characteristic of what makes us human. One theory, propounded by early twentieth-century experts such as the Australian palaeoanthropologist Raymond Dart, posits that walking on two legs developed because, as the climate changed, there was less woodland and more grassland, making bipedalism a more efficient way of moving around. There was a long intermediate stage, during which bipedal hominins still had a divergent big toe for climbing up trees to escape predators on the ground and could swing from branch to branch with their rotating wrists.

Once hominins became upright around 4.4 million years ago, anatomical changes to the hands, shoulders, elbows, pelvis and spine took place. As the evolutionary chain developed, they began to look more like humans today.

Toumai, 7 million years ago

Scientists wanted to establish the date at which our human line diverged from other primates, and the breakthrough came in 2001. After a decade of digging through the sand dunes in the Sahara of northern Chad, a FrancoChadian team of palaeontologists were rewarded for their efforts. They found fossilised bones, a partial skull and a mandible, ascribed to an ape-man who they dubbed Toumai, meaning 'hope of life' in the local Daza language. Some experts believe Toumai, known as Sahelanthropus tchadensis, was from a species of primate that was a common ancestor to both humans and chimpanzees. Molecular evidence suggests that Toumai lived close to the gorilla/chimpanzeehuman divergence approximately 7 million years ago, but it is not known if he or she was at times bipedal. This was nevertheless the point at which the evolutionary process that made us fully upright began.

About 2 to 3 million years ago there was a big freeze that killed the majority of animal life on land and sea. Africa was the region least affected by the Ice Age and life continued to flourish there. As wet, warm grasslands spread across the continent, these habitats created the perfect conditions for the evolution of the great apes: gorillas, chimpanzees and later the hominins or hominids (creatures between ape and human), from which we modern humans finally appeared. These primates gingerly came down from the trees to inhabit the ground and placed their safety in their wits rather than their strength.

It was the Victorian biologist Charles Darwin who first made the observation, in his 1871 book The Descent of Man, that since the African gorilla and chimpanzee are most like us in terms of their anatomy, and because they only existed in Africa, then humans must have originated there. Although Darwin's reasoning may not meet today's scientific standards, he had advanced a ground-breaking theory that creationists and many religious conservatives found abhorrent.

Gorillas are now only found in a few places in Africa, mainly in the Great Lakes region. More than a third of the 1,000 surviving mountain gorillas live under protection in the wild forests of the Virunga National Park. The mountains, a chain of volcanoes, span parts of Rwanda, the Democratic Republic of the Congo (DRC) and Uganda. I set off to see these endangered creatures in northern Rwanda, a mission that involved a long hike starting at dawn, through masses of thick vegetation glistening with morning dew. My exertions paid off when I eventually spotted the gorillas through the foliage. A couple of adult gorillas, including one majestic silverback, lay indolently on the ground—seemingly revelling in the early morning sunshine, while a pair of young gorillas tumbled down from a mound and played together on the muddy earth. It was remarkable to see how similar they are to humans. They live in family groups and their movements, antics and expressions are so like ours. In fact, data shows that humans and gorillas differ in only 1.75 per cent of their DNA, far less than previously assumed. (Chimpanzees—our closest relatives—differ only 1.37 per cent from our genomes.)

Once Charles Darwin had advanced his theory that humans originated in Africa, other scientists began to try to piece together the evolutionary chain from gorillas and chimpanzees to humans by studying extinct species of hominins and looking at bipedalism in particular. Bipedalism, which occurred about 6 million years ago, meant a primate's hands could remain free. About 3 million years later, this led to hominins being able to use their intelligence to make tools or hunt with weapons, assisted by their ability to rotate the wrist, a feature unique to apes and humans. Habitual bipedalism, the ability to walk permanently on two legs, is a defining characteristic of what makes us human. One theory, propounded by early twentieth-century experts such as the Australian palaeoanthropologist Raymond Dart, posits that walking on two legs developed because, as the climate changed, there was less woodland and more grassland, making bipedalism a more efficient way of moving around. There was a long intermediate stage, during which bipedal hominins still had a divergent big toe for climbing up trees to escape predators on the ground and could swing from branch to branch with their rotating wrists.

Once hominins became upright around 4.4 million years ago, anatomical changes to the hands, shoulders, elbows, pelvis and spine took place. As the evolutionary chain developed, they began to look more like humans today.

Toumai, 7 million years ago

Scientists wanted to establish the date at which our human line diverged from other primates, and the breakthrough came in 2001. After a decade of digging through the sand dunes in the Sahara of northern Chad, a FrancoChadian team of palaeontologists were rewarded for their efforts. They found fossilised bones, a partial skull and a mandible, ascribed to an ape-man who they dubbed Toumai, meaning 'hope of life' in the local Daza language. Some experts believe Toumai, known as Sahelanthropus tchadensis, was from a species of primate that was a common ancestor to both humans and chimpanzees. Molecular evidence suggests that Toumai lived close to the gorilla/chimpanzeehuman divergence approximately 7 million years ago, but it is not known if he or she was at times bipedal. This was nevertheless the point at which the evolutionary process that made us fully upright began.