Johannesburg, South Africa. T HERE is something very odd about Homo sapiens . Unlike other animals, we have no brother and sister species to share our world.
Horses have zebra siblings, dolphins have porpoises and lions have tigers.
But we are home alone, the only two-legged intelligent primate on Earth. It was not always so. More than 20 types of human being are now known, and the total is rising inexorably as scientists make more and more discoveries. In the past three years finds in Chad, Ethiopia and Spain have added three new types of human being to our family tree. These critical questions have been raised by leading palaeontologists and archaeologists in a spate of recent articles and newspapers in journals that include the latest issues of Scientific American and British Archaeology .