Science: The Truth About... The Missing Link

ONE OF the greatest myths of human evolution is that there is a "missing link" that will provide palaeontologists with the final piece in the historical jigsaw of Man. The fact is that there are hundreds or thousands of missing links in the complex, long-winded tale of how a tree- climbing ape came down to the forest floor, and started to walk upright and develop the intellectual capacity to speak and think.

This does not mean, however, that the story is lost for ever. A few critically important fossils, dating to various points in the period that has elapsed since humans and apes shared a common ancestor, have enabled experts to build up a remarkable picture of how humankind evolved into what we are today.

One of the most remarkable fossils will undoubtedly turn out to be the oldest complete skeleton of a hominid - an ape-like creature that is not quite fully human - which was discovered in the limestone caves of Sterkfontein near Krugersdorp in South Africa. Philip Tobias, emeritus professor of palaeontology at the University of Witswatersrand, who has been in charge of the site's excavation for 30 years, said this week that the skeleton is "probably the most momentous find ever made in Africa".

The skeleton is of a 4-ft-tall creature that lived between 3.22 and 3.6 million years ago, and scientists have classified it as a member of the group known as Australopithecus. Raymond Dart, the renowned Witwatersrand palaeontologist, first coined the name in the 1920s after discovering the front half of a 2.5-million-year-old skull, with jaws and teeth, of what is known as the "Taung child", after the place it was found. Dart gave it the scientific name Australopithecus africanus - southern ape of Africa.

Several species of the Australopithecines have since been described, including the famous 3-million-year-old "Lucy", a half-complete skeleton discovered in 1974 in the Afar region of present-day Ethiopia. Lucy, a female barely 3ft tall, seemed to offer the first glimpse of the anatomical adaptation to bipedalism, according to the palaeoanthropologist Richard Leakey. "By definition, the first hominid species to have evolved, some 7 million years ago, would have been a biped ape of sorts. But until the Lucy skeleton came along, anthropologists had no tangible evidence of bipedalism in a human species older than about 2 million years."

Tantalising remnants of skeletons, bits of bones and half-complete skulls, have been found of hominid-like animals even older than the Sterkfontein skeleton. The most famous is Ramipithecus, found in India and Kenyapithecus, in east Africa, dated to perhaps 14 million years old. Although these were originally thought to be "missing links" in the line of human evolution, scientists now believe they were related to other lines of apes that diverged from the hominids who evolved into humans.

It is another ape-like creature, Ardipithecus ramidus, alive about 5 million years ago, which is the strongest contender for ancestor of the Australopithecines.

Ardipithecus was not blessed with a large brain but its upright gait was clearly adapted to a life spent out of the trees for at least some of the time. It took another 2.5 million years, after the Australopithecines had evolved into even more human-like creatures, for the first true human - Homo habilis - with its greatly increased brain capacity, to appear. As the name suggests, H habilis was handy with tools.