Who are you? How the story of human origins is being rewritten

WHO do you think you are? A modern human, descended from a long line of Homo sapiens? A distant relative of those great adventure-seekers who marched out of the cradle of humanity, in Africa, 60,000 years ago? Do you believe that human brains have been getting steadily bigger for millions of years, culminating in the extraordinary machine between your ears?

Think again, because over the past 15 years, almost every part of our story, every assumption about who our ancestors were and where we came from, has been called into question. The new insights have some unsettling implications for how long we have walked the earth, and even who we really are.

Once upon a time, the human story seemed relatively straightforward (see blue text in timeline, below). It began roughly 5.5 to 6.5 million years ago, somewhere in an east African forest, with a chimpanzee-like ape. Some of its descendants would eventually evolve into modern chimps and bonobos. Others left the forest for the savannah. They learned to walk on two legs and, in doing so, launched our own hominin lineage.

By about 4 million years ago, the bipedal apes had given rise to a successful but still primitive group called the australopiths, thought to be our direct ancestors. The most famous of them, dubbed Lucy, was discovered in the mid-1970s and given arch-grandmother status. By 2 million years ago, some…