Science course part IV: Humans

The ages of man

From the tiny 'Hobbit' to the burly Neanderthals - a variety of other hominids once preceded and coexisted alongside us Homo sapiens, says Robin McKie

It is common to depict the evolution of Homo sapiens as a straight sequence in which ape-like beings turn into upright, big-brained humans, a linear march that suggests humans were an inevitable biological outcome once apes had begun to walk on two feet. But the notion is misleading, say experts. As palaeontologist Stephen Jay Gould once pointed out, we should not confuse evolution with progress: "Life is a copiously branching bush, continually pruned by the grim reaper of extinction, not a ladder of predictable progress."

In other words, our evolution was not a business in which one apeman species was replaced every so often by a new, improved version until, eventually, Homo sapiens appeared on the scene. It was a process of experimentation in which our hominid ancestors evolved in several different directions. Thus for the past 5m years there were usually several different types of hominid species competing with each other.

So let us look at some of those different hominids that peopled the Earth, starting from the remote past and moving to the present. We should note the trend towards increased brain power and general sophistication but resist the idea that modern humans were the pre-destined outcome of this sequence.

Australopithecus anamensis

One of the earliest species of apeman, its bones were discovered by Maeve Leakey in Kenya and dated as being 4.2m years old. Anamensis clearly walked upright, and to judge from the seeds found with its bones, this chimp-sized apeman was still spending much of its time in woodland and had not yet completely acclimatised to life on the open savannah.

Australopithicus afarensis

This species, the southern ape from Afar (an area in Ethiopia), is best known by the skeleton Lucy, discovered in 1974 by US palaeontologist Don Johanson. Afarensis - whose remains have been dated as being between 3m and 4m years old - was little bigger than anamensis. Its diet appears to have been mainly vegetarian. Interestingly, its skeletons vary from 1 to 1.5m in height, which suggests the species may have been dimorphic, like gorillas, which have large-bodied males who compete for access to groups of smaller females.

Australopithecus africanus

Another ape-like predecessor of modern humans, africanus was discovered by Raymond Dart in 1925 and provided the first solid evidence that mankind's roots were African and not Asian as many scientists then thought. Africanus thrived between 3.5m and 2.5m years ago and had roughly the same stature as afarensis - although its front teeth were smaller and its face slightly flatter. It, too, was mainly vegetarian in diet.

Homo habilis

The first hominid species to make stone tools, Homo habilis - meaning handyman - was discovered by the fossil-hunting husband-and-wife team Louis and Mary Leakey, the parents of Richard Leakey, in the Olduvai Gorge in Tanzania in 1960. Its anatomy is poorly understood due to a lack of specimens, although the skulls that have been found suggest a brain capacity of about half that of modern man but twice that of australopithecine apemen.

Homo erectus

The most perfectly preserved specimen of Homo erectus was found by a team led by Richard Leakey and Alan Walker on the banks of the river Nariokotome in Kenya in 1972. Dated as being about 1.5m years ago, the Nariokotome boy appeared to have been nine to 11 years old when he died. He was already 1.6m tall, however, and would have been around 1.9m if he had reached adulthood. This tall, cylindrical shape suggests Homo erectus must have been highly active, a hunter on the savannah who needed to lose heat with maximum efficiency. He would have sweated heavily and almost certainly would have lost the fur of his ancestors. Hairless humans had arrived.

Homo heidelbergensis

Remains of this robust, thick-boned species were first found near Heidelberg (hence the name). In addition, teeth and leg bones have been dug up at Boxgrove in West Sussex. Heidelbergensis - whose remains have been dated as being 400,000 to 500,000 years old - was clearly an adept hunter and a skilful weapon-maker to judge from the fine stone axes left near the sites where it killed and butchered animals such as horse and rhinos.

Homo neanderthalensis

Neanderthals first appeared in Europe about 250,000 years ago. They were thick-set, mighty hunters who survived at least two Ice Ages before abruptly disappearing from the continent about 35,000 years ago. Neanderthals buried their dead, suggesting they possessed spiritual beliefs, and made highly sophisticated stone tools. DNA studies also indicate they may have possessed the power of complex speech - and red hair. Exactly why they perished while modern humans thrived is still unclear.

Homo floresiensis

Easily the most controversial hominid fossil find of recent years, remains of Homo floresiensis were discovered on the Indonesian island of Flores by a team led by Peter Brown of the University of New England, Australia. Believed to be descendants of Homo erectus who settled on a group of islands in the area, Flores man was only a metre high with a small brain. Its skulls, bone fragments and stone tools have been dated as being between 94,000 to 13,000 years old. Its tiny stature led to it being nicknamed the Hobbit, though some scientists claim the fossils are merely the remains of deformed modern humans suffering from microcephaly, a congenital shrinking of the skull.

Homo sapiens

Distinguished by its relatively slender physique, at least compared with burly Neanderthals, our species - Homo sapiens or "wise man" - is distinctive for its large brain, tool-making expertise, capacity for symbolic thought, use of language and ability to cooperate. Such attributes have made us formidable hunters, producers of great artistic works, and polluters on a vast scale. They have also brought us world domination. For the first time in the past 4m years, the planet has only one species of hominid: Homo sapiens.

Today's best video

Today in pictures