Human evolution and the first Australians

Our place among the apes

Humans are primates, and our closest living relatives are chimpanzees and bonobos, then gorillas, then orangutans. Humans did not evolve from chimpanzees. Instead, humans and chimpanzees share a common ancestor that lived in Africa about 6 to 7 million years ago. Since then each lineage has evolved separately. The group that includes humans and all our extinct relatives since that split is called the hominins.

The key features that distinguish hominins evolved at different times:

• Walking upright on two legs (bipedalism) came first. Bipedal hominins have a skull opening for the spinal cord (foramen magnum) underneath, an S-shaped spine, a short bowl-shaped pelvis, thigh bones angled in towards the knees, and an arched foot with a big toe in line with the others. Footprints at Laetoli in Tanzania show hominins walking upright 3.66 million years ago.
• Smaller canine teeth and a flatter face.
• Larger brains came much later, mainly in the last 2 million years, along with stone tools, use of fire and complex culture.

A bush, not a ladder

Old pictures show a single line of ape-like ancestors marching towards a modern human. The fossils show something very different: a branching bush, with several hominin species often alive at the same time, and most branches ending in extinction.

• Early hominins such as Sahelanthropus (about 7 million years ago, Chad) and Ardipithecus (Ethiopia) show the first signs of upright walking.
• Australopithecines walked upright but had small, ape-sized brains. The "Taung child", found in South Africa in 1924 and described by Raymond Dart in 1925, was the first australopithecine discovered. "Lucy", a 3.2-million-year-old Australopithecus afarensis skeleton about 1.1 m tall, was found in Ethiopia in 1974.
• Early Homo, such as Homo habilis, appeared about 2.4 million years ago with larger brains and stone tools. Homo erectus was the first hominin to leave Africa, reaching Georgia by 1.8 million years ago and later Java and China, and survived in Java until about 110 000 years ago.
• Neanderthals lived in Europe and western Asia from about 400 000 to 40 000 years ago, with brains as large as ours. They made complex tools, used fire, cared for the sick and buried their dead.
• Our own species, Homo sapiens, appears in Africa about 300 000 years ago: the oldest fossils, from Jebel Irhoud in Morocco, were dated in 2017.

Discoveries that changed the story

Some of the biggest discoveries in human evolution have come since 2003, and several were made in our own region:

Ancient DNA has also shown that our species interbred with other hominins. People with ancestry from outside Africa carry about 1–2% Neanderthal DNA. People in Papua New Guinea and many Aboriginal Australians carry a few per cent of Denisovan DNA. Some of these inherited alleles were favoured by natural selection: a version of a gene called EPAS1, inherited from Denisovans, helps many Tibetan people live at high altitude with little oxygen.

The first Australians

During the ice ages, sea levels were up to about 120 m lower than today. Australia, New Guinea and Tasmania were joined in one continent called Sahul, and much of South-East Asia formed a continent called Sunda. But deep water always separated the two, along Wallace's Line. Even when sea levels were lowest, people reaching Sahul had to cross open sea between islands, in places tens of kilometres wide. These were among the earliest deliberate sea voyages known anywhere in the world.

At Madjedbebe, a rock shelter on Mirarr Country in western Arnhem Land, archaeologists working in partnership with the Mirarr Traditional Owners excavated stone tools, grinding stones and ground ochre. In 2017 they reported that the oldest layers are at least 65 000 years old. Some researchers argue for a younger date of about 50 000 to 55 000 years, but either way, First Nations peoples have lived in Australia for many tens of thousands of years, through ice ages, the loss of the megafauna and huge changes in sea level and climate: the oldest continuing cultures on Earth. Many First Nations people express this as having been on Country since the beginning, and the scientific dates are consistent with that deep connection.

At Lake Mungo in the Willandra Lakes, on the Country of the Paakantyi (Barkindji), Mutthi Mutthi and Ngiyampaa peoples, the remains known as Mungo Lady and Mungo Man are about 42 000 years old. Mungo Lady was cremated and Mungo Man was buried with red ochre: among the oldest known ceremonial burials in the world. After decades in university collections, both were returned to Country at the request of their descendants. Nearby, hundreds of human footprints about 20 000 years old record adults and children walking across wet clay.

DNA studies published in 2016, carried out with the consent and involvement of Aboriginal communities, found that Aboriginal Australians and Papuans descend from one of the earliest groups of modern humans to leave Africa, and that Aboriginal populations in different regions have been separate for tens of thousands of years, matching the great diversity of languages and nations across the continent.

Are humans still evolving?

Yes. In the last 10 000 years, alleles that let adults digest the milk sugar lactose became common in populations that farmed cattle, goats or camels. Alleles that protect against malaria, such as the sickle cell allele, are common where malaria is widespread. The Bajau people of South-East Asia, who have dived for food for over 1000 years, have larger spleens that help them stay underwater longer. Natural selection continues wherever some inherited variation affects survival and reproduction.