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By Root 576 0

erectus had remained relatively narrow, restricting erectus brains at birth to be no larger than 230 cubic centimetres. But in 2001, researchers at Gona in Ethiopia—an area adjacent to Hadar, where Lucy was found—discovered the almost complete pelvis of a 1.2-million-year-old erectus female that produced a dramatic new perspective. Piecing the pelvis fragments together, they were struck by its unusual width. Homo erectus, it turned out, had performed an evolutionary leap making it capable of producing babies with brains at birth much closer in size to modern humans. The short-statured Gona female had hips that were proportionally wider than those of modern humans, with a birth canal more than 30 per cent larger than previous estimates, allowing for the delivery of a baby with a brain as large as 315 cubic centimetres; by comparison, a modern human baby’s brain at birth is about 380 cubic centimetres.

Being born with a proportionally larger brain meant that erectus babies probably became independent far more quickly than modern human infants—a useful survival adaptation in the African savannah. The female pelvis, meanwhile, still remained narrow enough to make bipedal locomotion reasonably efficient.

By 1 million years ago, the only surviving hominid species on earth was Homo erectus, strung out over three continents: Africa, Asia and Europe. Mary Leakey, noting how erectus in Africa had kept turning out the same Acheulean hand-axes for hundreds of thousand of years, attempting no innovation, referred to erectus as a ‘dim-witted fellow’. Yet erectus enjoyed a lifespan on earth longer than any other hominid species, surviving from almost 2 million years ago through periods of extreme climate variation to about 200,000 years ago and possibly beyond; one recent discovery of fossil skulls in Java placed erectus living there only 50,000 years ago.

An even more intriguing discovery was made on the remote Indonesian island of Flores in 2003. A team of palaeontologists excavating a cave at Liang Bua uncovered the skull and partial skeleton of a tiny human female, no more than three feet tall, with a brain size of only 417 cubic centimetres. Because of its small size, they nicknamed it ‘the hobbit’. Their initial assessment, published in Nature in 2004, was that it belonged to a diminutive new species descended from an ancestral population of Homo erectus which had become isolated on Flores and had evolved into miniature form as a result of ‘island dwarfism’. They subsequently found six other ‘hobbits’, all of them of similar size. Dating the specimens indicated that the hobbits had survived until as recently as 17,000 years ago. Sceptics argued that they were simply modern people who had suffered from some kind of pathological condition, such as microcephaly or a similar disorder. But further investigations presented more of a puzzle. Several features of the feet suggested that they were more akin to an even earlier species than Homo erectus—that is, to Homo habilis. Scientists who reviewed hobbit research at a symposium at Stony Brook in 2009 concluded that they merited inclusion as a new human species: Homo floresiensis. Stone tools found on Flores indicate that the island may have been occupied as far back as 1 million years ago.

About 700,000 years ago, during a period of severe climate fluctuations, a new contender appeared on the scene in Africa with an even bigger brain. Whereas brain size between 1.8 million and 700,000 years had remained remarkably stable at about 65 per cent of the modern average, it now increased to about 90 per cent. Like erectus, the new arrival spread rapidly to Europe. The first clue to its existence came from a gravel pit at Mauer, near Heidelberg in Germany; in 1907, workmen found a strange-looking lower jaw with a complete set of teeth which were clearly human, though the thickness of the jawbone seemed more apelike. As it was unlike any previous discovery, it was assigned a new name: Homo heidelbergensis. Fourteen years later, in 1921, miners cutting through an extensive limestone cave