In the past, there were many species in the Homo genus. Today, there remains only Homo sapiens. We are the sole survivors of an evolutionary line with many ramifications. "We are unique quite simply because we are alone," writes Pascal Picq. RTD info meets a paleoanthropologist and lecturer at the Collège de France engaged in a relentless pursuit of our most distant origins.
Charles Darwin believed the origins of humanity lay in Africa, because that was where his 'cousin' the chimpanzee was also found. Do we have an increasingly precise idea of the relationship between humans and other apes?
|In the wild, chimpanzees adapt to theirenvironment, hunt, are omnivorous, havesocial rules and a hierarchy, feel empathyand sympathy, are able to deceive andmanipulate. These are all characteristics with whichwe can identify and that stem from acommon heritage.|
© Michel Van den Eeckhoudt
For a long time, we believed that any evolutionary trait was an indication of the human line and any archaic trait indicative of the chimpanzees. The evolutionary system in the neo-Darwinian tradition classifies species into families. Each family is attributed an environment to which it has adapted. Viewed in this way, the great apes (chimpanzees, gorillas, orang-utans) are placed in the pongid family, while humanity belongs to the more evolved hominid family.
In this context, the great apes are seen as an ancestral line of the human species, with a number of 'missing links' that remain to be discovered. But there is another way of looking at it: one of a common ancestor rather than missing links. The phylogenetic or cladistic system, which is more recent in its concepts and rooted in genetic characteristics (molecular system), is based on relationships of kinship and defines branches – known as clades. This system first searches for relationships between groups and then deduces the evolutionary processes, whereas the evolutionary system first proposed an evolutionary schema and then deduced the classifications. In the phylogenetic view, species are grouped into the same clade if they share the same derived states of a characteristic.
Take, for example, the trout, the lungfish – a fish with both lungs and gills – and the cow. A classification into evolutionary families would put the two fish into the same category. A cladistic analysis, on the other hand, would place the lungfish and cow together because they both possess, in the derived state, an aerial respiratory system.
As for the great apes and modern humans, they can be divided into two lines: the African line (humans, chimpanzees and gorillas) and the Asian line (pongids, in which there are only orang-utans). Humans and Africa’s great apes possess a recent and exclusive common ancestor. But we only know a part of their evolutionary tree.
This other approach to evolution, that of ramifications rather than a straight line, calls into question the notion of progressive development, of a human race that became progressively better adapted to its environment and increasingly skilled and able.
Evolution is not 'linear'. A progression in terms of an increasingly upright biped, an increasingly large brain, increasingly dexterous hands, the creation of tools and socialisation is a schematic and obsolete view.
There is not one biped but several bipeds, and the great apes can also walk upright. For a long time it was thought that man stood up when he started to live in the savannah so that he would be able to see predators approaching. But this aptitude for standing on two feet existed in our ancestors living in the forests of Africa more than 6 million years ago. Then this aptitude, that was advantageous in a new environment, became an adaptation.
The use of stone tools – another example – is a trait of hominids, but not of the Homo genus. Tools between 2.6 and 2.3 million years old have been found in Ethiopia (at Kada Gona) and Kenya (at Lokalelei). The Lokalelei site is like a workshop, strewn with tools. Silex, basalt and quartzite were all used as raw materials to produce cutting objects that could be used to butcher or dismember animals, as well as to provide access to a variety plant-based food. The striking and fracture patterns indicate skilled individuals who used their right hand. An Australopithecus discovered in Ethiopia, estimated to have lived 2.5 million years ago, was found close to chiselled tools that must also have been used as an aid to eating meat.
But chimpanzees do not work stone.
No, but they break open nuts using stone or wood objects that function as tools and transmit this know-how from generation to generation. They can walk standing up, adapt to their environment, hunt, are omnivorous, live in communities, possess social rules and a hierarchy, are conscious of themselves, can feel empathy and sympathy, and know how to deceive and to manipulate. These are all traits with which we can identify and that come from this common heritage.
Do we already suspect 'someone' of being this common ancestor?
We seem to be getting close to finding one – and that is sparking controversy. Two fossils confirm the origins of a common human line in Africa. One, known as Orrorin, found in Kenya in 2000, is 6 million years old. The other, known as Toumaï, was discovered in Chad two years later and is estimated to be 7 million years old. So, they are situated around the time of the separation into the panins, which the Orrorin resembles by virtue of the teeth, and the hominins, with which it shares the ability to stand upright. All we share with Toumaï is the skull, but the position of the occipital hole – into which the backbone slots – suggests to us that they could also have walked upright. The teeth, with rather poorly developed canines, also place it close to hominids. But which of the two is the closest to our most recent common ancestor? That we do not know, but there are only two candidates – while we await further discoveries.
Orrorin and Tourmaï are, therefore, much older than the famous Lucy.
Yes, Lucy is an Australopithecus, discovered in 1974 in the Afar region of Ethiopia by Yves Coppens, Maurice Taïeb and Donald Johanson. Her skeleton was very complete and she was the oldest known human, between 3 and 4 million years old. We know that Australopithecus could stand upright and walk, but it was an unstable walk that involved a rotation of the hips, a fact we can deduce from the shape of the pelvis and limbs. They also retained all their aptitudes for moving around in trees. Their cone-shaped rib cage only allowed air to enter by movements of the diaphragm which meant that they were unable to run long distances. Their molars were coated in a thick enamel and their mandibles were strong, enabling them to chew tough food. Their already developed brain required considerable amounts of quality nutrition. Australopithecus is, therefore, the first known group in the evolutionary line, but it is diverse and we do not know which strand is the closest to the origin of the Homo genus.
Why was it that Australopithecus disappeared relatively quickly?
They disappeared due to climate changes that dramatically altered the planet between 2.5 and 3 million years ago. Africa dried up, the savannah expanded, the grass species multiplied and the fauna was renewed. In this new biotope, new hominids appeared: the Homo and the Paranthropus. They shared a more evolved brain than the Australopithecus and were more distinctively bipedal. But there were differences between them, in particular in terms of size and teeth, and these differences grew from 1.5 million years ago, in what is known as ecological divergence.
The first incontestable representative of our genus is Homo ergaster, who appeared in Africa between 1.8 and 2 million years ago. It is associated with two types of culture – the Odowayen and the Acheulean. Later, between 110 000 and 40 000 years ago, we are confronted with two types of human: Homo neanderthalensis and Homo sapiens, both associated with a single culture, the Mousterian culture.
What was Homo ergaster like?
They were tall – over 1.70 m – perfectly bipedal, and able to live without the protection of trees. Their brain capacity was between 700 and 850 cm3. Their anatomy enabled them to walk long distances and to run in the vertical position, which is an advantage when moving around in the savannah and steppes. Running became possible due to changes in their morphology. Their larger cranium limited oscillations of the upper body compared with the pelvis. Their shoulders were broad, distancing the arms from the torso and making the upper body more stable. The lower limbs were long, the thigh and leg were aligned by means of an articulation of the stabilised knee, the foot was short and compact.
Homo ergaster quickly spread. It inhabited the whole of Africa and soon reached Europe and Asia, between 1.5 and 2 million years ago. Fossils found in the province of Java, in Georgia, confirm the presence of Homo erectus about 1.7 million years ago, and then Homo heidelbergensis in Europe in Ceparano (Italy, 900 000 year ago) and in Grand Dolina (Spain 800 000). About 1.2 million years ago, when there was a notable cooling, the only hominin to survive was the Homo genus. But in fact, since Homo spread outside of Africa, we do not really know how many human species succeeded one another or co-existed. Take, for example, the recent discovery of a small species of man, Homo floresiensis, who lived in isolation on the island of Flores, east of Java, and who died out about 18 000 years ago, at about the same time as Homo sapiens was painting the Lascaux caves, that is 15 000 years after the disappearance of the last Neanderthals in Europe.
Does biotechnology, DNA techniques for example, help you with this kind of research?
The high hopes of fossil DNA readings have been reduced considerably. The only pertinent elements concern Neanderthals (Homo neandertahlensis) and Cro-Magnon (also known as Homo sapiens). They support our belief that the Neanderthals and Homo sapiens were perhaps different species that split into two different lines about 700 000 to 800 000 years ago. The Neanderthal line evolved in Europe about 600 000 to 700 000 years ago while the Cro-Magnon comes from Africa.
Similar scenarios certainly apply to the isolated populations of Java (Homo soloensis) and Flores (Homo floresiensis). Neanderthals and Cro-Magnon were both present at the same time in Europe at some point but do not seem to have interbred. The question is whether Neanderthal is a distinct species or a sub-species of Homo sapiens? The few comparative studies carried out on fossil DNA suggest a different species. However, the Neanderthals buried their dead, so one can speak of a common humanity. But one must be careful not to confuse concepts. When one speaks of species, one is reasoning in terms of biology, when one speaks of humanity or the human, one is entering the field of philosophy and the human sciences.
And today, do we no longer speak of species or human lines?
The situation is paradoxical. We now know, thanks to the various fossils discovered, that Australopithecus, Paranthropus and humans could have been contemporary at all times in our evolutionary past. Until 35 000 years ago, Neanderthal and Cro-Magnon man co-existed in Europe. At the same time, there were other species on the island of Flores. The disappearance of Neanderthal from Europe about 30 000 years ago, and of the little people from Flores about 18 000 years ago, marked the end of a plural humanity. After that, just one human species– the Cro-Magnon, which is us – dominated the Earth. We are the last representatives of the grand line of the hominins.