Can lizards and cockroaches coexist?
Today we are the only human species to inhabit the earth - and we consider that to be completely normal. In most of the last four million years of our evolution several hominid species have lived at the same time. We have only been alone for about 25,000 years, without any competition.
For a long time, many scientists did not realize that the sole existence of Homo sapiens was the exception in the history of human evolution. In the fifties and sixties an anthropological tendency emerged which claimed that our planet could at any time offer space for at most one culture-producing species.
Even then, this view (the "one-species hypothesis") was not really convincing, although 35 years ago there were far fewer hominid fossils than there are today. But apparently a straightforward, "linear" evolution towards modern Homo sapiens corresponds too much to wishful thinking: the slow transformation of a stooped, dull ape-man into the graceful, highly intelligent ruler of the world.
It was not until the late 1970s that paleontologists abandoned this hypothesis. In the meantime they had discovered fossils which clearly proved that several hominid species lived simultaneously in the region of what is now northern Kenya about 1.8 million years ago. However, some scientists still tried to keep the number of species as low as possible. They played down differences between fossil bones as much as possible. This is how the rather meaningless collective term "archaic Homo sapiens" came about.
To this day, many anthropologists believe in a rather small number of hominid species. It is absolutely clear that in the evolution of hominids it was quite normal for different prehistoric or early human species to assert themselves side by side. This group of primates resembles many other successful systematic families in the animal kingdom. Our own development history is also characterized by diversity and not by straightforward further development.
Again and again new hominid species emerged, they had to compete with others, sometimes had more, sometimes less success, sometimes spread, sometimes they disappeared again. We will probably never fully find out why, in the end, only modern man was left. At least Homo sapiens itself provides us with some interesting clues: He met the Neanderthals in two regions, first in the Middle East, where both species lived side by side for a long time, and later also in Europe, where the Neanderthals soon disappeared.
The species of early and prehistoric humans discovered so far fill a fairly long list. And the diversity we know goes back almost to the beginning, when the first upright hominid - the first "Australopithecine" - gradually ventured into open savannahs.
Multi-branched family tree
The oldest suspected hominid is currently Ardipithecus ramidus. He lived around 4.4 million years ago. Paleontologists discovered bone fragments near Aramis in Ethiopia (see "Early Hominids" in Spektrum der Wissenschaft, 8/97, p. 50).
The better known Australopithecus anamensis is only a little younger. Scientists found its fossils in northern Kenya in geological layers that are 4.2 million years old.
It is true that Ardipithecus was probably already walking upright. But in many ways it was still very similar to the great apes. The A. anamensis is completely different: this early hominid already had a clear similarity to the Australopithecus afarensis. A. afarensis is well known from many fossils. It also includes the famous "Lucy", a fragmentary female skeleton. A. afarensislived in different parts of East Africa 3.8 to 3 million years ago. The 3.18 million year old "Lucy" comes from the Hadar region in Ethiopia.
The A. afarensis species walked upright, still had a very small brain and a face that was large in proportion to it. Some researchers suggest that it was really more than one species. But even if future research should prove otherwise, these beings weren't the only hominids in their day. A lower jaw recently came to light in Chad, which researchers believe is a fossil of a new species. They named her Australopithecus bahrelghazali. They estimate the age of the fossil to be 3.5 to 3.0 million years.
Recently, South African scientists discovered fossils near Johannesburg that probably suggest another species of hominid from the early period. She doesn't have a name yet. The find is 3.3 million years old. This species also walked upright.
The species Australopithecus africanus later lived in South Africa - three to probably almost two million years ago. It was there in 1924 that paleontologists found the first Australopithecus ("southern monkey").
A 2.5 million year old species from Ethiopia was recently given the name Australopithecus garhi. According to anthropologists, this species occupies an intermediate position A. afarensisand several younger species belonging to two groups: On the one hand, there are further australopithecins, in this case called "robust" and assigned to the genus Paranthropus; others already belonged to the genus Homo, so were early "humans".
About the same age as A. garhi is the oldest Australopithecine of the "robust" group, Paranthropus aethiopicus, best known for the 2.5 million year old "Black Skull", a black skull from Northern Kenya. The "robust" group also includes Paranthropus boisei, which was widespread in eastern Africa 2.0 to 1.4 million years ago. "Robust" species also lived in South Africa: around 1.6 million years ago the P. robustus, directly named in the species name, and perhaps a second species closely related to it, P. crassidens.
With this list I have expected a lot from you. In truth, however, the Australopithecines tended to include even more species. And unfortunately we don't yet know how long each of them really lived. But even if the individual species only survived an average of perhaps a few hundred thousand years - it is certain that Africa, from the beginning of human evolution, has at many times, probably always, been home to several hominid species at the same time.
It stayed that way when the genus Homo appeared. Anthropologists place hominids in this genus with a significantly larger brain. We know the earliest representatives of Homo through a strange hodgepodge of 2.5 to 1.8 million year old South and East African fossils. Paleanthropologists usually attribute these fossils to two types: H. habilis and H. rudolfensis. But it was probably a lot more. In addition, 1.9 to 1.8 million years ago, it was not just the ubiquitous mentioned above that did the homo species P. boiseiSociety, but also the Homo ergaster, a creature with a visibly "modern" physique. (In the past, the experts called this African as well as certain Asiatic lines H. erectus; the name applies only to early Asiatic hominids today. (See also: "A new model of the homo-Evolution ". By Ian Tattersall, Spektrum der Wissenschaft, 6/97, p. 64). Thus at least four hominid species shared the same East African habitat at that time.
When people left their continent of origin for the first time, they found plenty of new space in which to develop. Probably at that time H. ergaster or a close relative of his set off from Africa. Unfortunately we know almost nothing about this migration, not even about the time periods. After all, we have evidence that humans reached China and Java around 1.8 million years ago. A lower jaw found in 1991 in Dmanisi, Georgia, and two skulls discovered in 1999, which belong to an early Homo erectus and Homo gassedr resemble.
In Asia, people continued to evolve. A million years ago the new species H. erectus was established in Java and China. It is possible that there was another, more powerfully built species living next to her in Java.
The alleged first humans in the far west of Eurasia looked markedly different from this East Asian line. Spanish researchers discovered fossils of the earliest Europeans in the north of their country a few years ago. This homo antecessor, as they called it, appeared there around 800,000 years ago.
The evolution of the Neanderthals took place in Europe and in regions of East Asia (see also "The special evolution of the Neanderthals", Spektrum der Wissenschaft, 7/1998, p. 56). Its early ancestor is Homo heidelbergensis, named after a lower jaw from Mauer near Heidelberg. The oldest fossils of this human species come from North Africa and are around 600,000 years old. European sites showed an age of 500,000 to 200,000 years; the fossil from Mauer is one of the oldest. And this human form may also have lived in China. However, I would not be surprised if further research would identify several species in the "Ureuropäer".
In any case, the H. heidelbergensis - or perhaps a relative - was the ancestor of the Neanderthal man, Homo neanderthalensis, and human forms close to him in Europe. The evolution of this circle was limited to Europe and western Asia. The Neanderthals, named after the first skeleton find in the Neandertal near Düsseldorf in 1856, experienced their heyday between 200,000 and 30,000 years ago. Back then, people in Africa seem to have gone through their own evolution. Even if the finds so far are rather meager, there is much to suggest that this continent, among other developments, produced Homo sapiens, the "modern" man. I will go into this in more detail later.
East Asia also evidently had a long separate history. Fossils from Ngandong on Java, possibly from Homo erectus, have just been re-dated to an age of only 40,000 years.
Thus, human evolution is by no means a relatively straightforward, single-minded development: from Australopithecus africanus to Homo erectus to Homo sapiens, as researchers mostly thought forty years ago. However, the fact that we know many more fossils today than we did then does not make the discussion among experts any easier. The idea of a linear evolution still throws its shadow: Many of my colleagues still believe that scientists are exaggerating when they postulate the existence of so many hominid species. Most counter-models with fewer species also reduce the number of homo forms. Some paleontologists believe that all people who have lived in the past 500,000 years are of a single species: Homo sapiens,others even all homosexuals from the past two million years.
I strongly disagree. In my opinion, with the assumed 20 or so hominid species - not all of which have been named yet - we are rather too low than too high. The fossils available to us are still full of indications of diversity from a morphological point of view, but most of them have so far been largely ignored. Furthermore, it would be rash to say that we know fossils of every species of hominid that has ever existed. But even if only the second statement is true, it definitely stays the same: The evolution of man was not a story of the struggle for existence of a single, lonely hominid line that followed its straight path.
But this story tells of repeated experiments, of how nature tinkered with. Our biological development did not progress evenly, always in the same direction, but rather sporadically, sometimes here and there. Over the past five million years, new species of hominid have appeared and disappeared regularly. How they dealt with each other, asserted themselves or failed, sometimes conquering new habitats, remains almost completely hidden from us. Only one thing seems certain: The human family tree developed in a highly changeable time full of innovations, shaped by mutual contacts. And there is no way Homo sapiens is at the top of that tree. Our species simply represents one of many branches.
And yet: Homo sapiens undoubtedly embodies something unique. This is clearly shown in the fact that we are the only kind of human today. Whatever makes us special - it has to do with how we deal with the outside world. So this uniqueness affects our behavior, and that means that archaeological finds in particular have to help. Archeology looks back about two and a half million years. At that time, people made the first recognizable stone tools: simple sharp-edged cuts that they chipped off from blanks with other stones. We do not know exactly which hominids invented this technique. There is some evidence that they belonged to the Australopithecines.
In any case, this invention represented a considerable intellectual leap. The simple blades and scrapers would bring users many advantages in their daily life in the future. Archaeologists are already talking about a real stone tool industry, albeit a simple one. For a million years the artifacts more or less stagnated at this level. Then humans - probably the H. ergaster - invented the hand ax one and a half million years ago. This technological innovation first required the manufacturer to imagine the symmetrical shape before starting to knock it out of the large pebble. Another million years, or even more, would pass before the next groundbreaking tool invention. The H. heidelbergensis or a related hominid came up with the idea of preforming a stone core so skillfully that a targeted blow suddenly produced the finished tool for cutting or scraping.
The Neanderthals proved to be particularly adept at this technology. We know of countless excellent documents from these people with their large brains, flat skulls and large faces, who inhabited Europe and Western Asia until around 30,000 years ago and were then suddenly ousted by modern humans. We can use them to gauge what H. sapiens was doing differently in comparison with the Neanderthal. H. neanderthalensis is quite impressive with its stone tools, even if they seem a bit stereotypical. However, he rarely, if ever, made tools from other durable materials. In addition, many archaeologists do not consider him a particularly skilled hunter.
Scientists previously suspected that the Neanderthals performed rites such as "bear cults", but no real evidence was found. They probably didn't make symbolic objects either - certainly not before they came into contact with modern humans. Sometimes they buried their dead, but perhaps only so that hyenas would not become a nuisance to them. Other profane explanations for this practice are also conceivable. At least they did not give the deceased any gifts in the grave that would testify that they performed funeral ceremonies or believed in survival after death. As admirable as the Neanderthals were in many ways - after all, they coped very well with the harsh, changeable climatic conditions of the late Ice Age for a long time - they lacked that spark of Homo sapiens creativity, which he brought to Europe.
When and where Homo sapiens originated, we do not know with absolute certainty based on fossils. Most of the arguments for an African origin maybe 150,000 to 200,000 years ago. Modern behavior patterns did not appear until much later, however. The best evidence of this comes from Israel and the surrounding area. Neanderthals lived in this region at least 200,000 years ago. Around 100,000 years ago, the anatomically modern Homo sapiens also came to this area.
Notably, both types used the same tools, and the spaces left behind look completely identical too. As far as we can tell, both types of people apparently behaved in the same way in spite of all their anatomical differences. And as long as both stuck to it, they also managed to share this living space in the Middle East with one another.
The situation in Europe could not provide a sharper contrast. The H. sapiens only got there around 40,000 years ago. And only 10,000 years later, the Neanderthals, previously ubiquitous, had disappeared. The decisive factor in what the new immigrants distinguished themselves was their "modern" emotional and spiritual feeling. According to numerous testimonies, H. sapiens fully developed this unprecedented trait when he came to Europe. On the one hand, these people made stone tools that we attribute to the Upper Palaeolithic: They knew how to get many long, slender blades very effectively from a cylindrically cut stone core. They also made tools from bones and antlers, with an excellent feel for the properties of the material.
More tellingly, these people knew art. They carved small sculptures, carved pictures, and painted cave walls, sometimes with vivid scenes. They noted important things on bones and stone plates. They also carved small flutes and made beautiful personal jewelry.Apparently they differentiated between social classes, because some of the dead received particularly rich grave goods. Accordingly, they believed in life after death. They structured their homes highly, and they must have been skilled hunters and fish catchers. For the first time in the history of hominids, technological innovations gave people an incentive to refine their skills more and more. The long section of discontinuous cultural development that stagnated over long phases was now over. From now on the skills grew steadily. In short: these people were like us!
The power of language
From the Neanderthals, the early Upper Paleolithic differed sharply in all these respects. It is true that some of the European "natives" seem to have copied some behavior from the newcomers. However, we do not have any specific information on how the two species interacted with each other. If we nevertheless suspect that the Neanderthals often got the worst, it is because they disappeared so quickly and because H. sapiens has now left its mark everywhere. The archaeological evidence clearly says the same thing over and over again: Modern man spread out in places where the Neanderthals had only recently lived. But this one had disappeared from there. Anthropologists cannot convincingly prove that the two human species ever mixed biologically in Europe.
In the Middle East, Neanderthals and H. sapiens had coexisted for around 60,000 years. But that ended almost exactly 40,000 years ago when the first Upper Paleolithic tools appeared there. Now suddenly the H. neanderthalensis had to give way - as it did in Europe - to a modern person who had now probably found a high quality culture.
Why did the two types of people in the Middle East initially endure side by side for a long time and why not in Europe from the outset? Most likely the crucial difference was that the H. sapiens100,000 years ago in the Middle East was not yet at the same intellectual and cultural level as the conquerors of Europe 60,000 years later. From an anatomical point of view, these people have long since represented the modern type, but in terms of behavior they remained stuck to the old patterns for a long time. They only acquired the "modern" patterns of thinking and thus behavior much later. It makes sense to equate the appearance of this new - modern - cognition with the appearance of symbolic thinking. And then suddenly Homo sapiens no longer tolerated the rival next to him, who he had perhaps always hated.
How did this spiritual revolution come about? An evolutionary process follows certain rules. Above all, something new can only occur within an existing species - where else? In addition, innovations often arise from the fact that something that has already existed (often for a long time) is placed in a different context. For example, the hominids had had a fundamentally modern vocal machine for several hundred thousand years. They don't seem to have used it for fully articulated speech by a long way, because their behavior does not show any signs of this.
But the phenomenon of emergence is also important: something fundamentally new, sometimes completely unexpected, can arise from several components that come together by chance. The classic example of this is water, the properties of which cannot be predicted from those of hydrogen and oxygen.
Put all this together, the process through which symbolic thinking arose was not all that unusual - even if the consequences of it revolutionized our behavior. So far, neuroscientists have no idea how our brain uses electrical and chemical processes to create the experience of consciousness. But somehow the transition from a preliminary stage to symbolic thinking must have taken place in our ancestors. The only plausible thing seems plausible is that existing traits were accidentally linked to a rather minor genetic innovation and that this gave rise to an unprecedented potential. This must have happened when the anatomically modern Homo sapiens appeared.
But this explanation is by no means sufficient, because after all, anatomically modern humans behaved archaically for a very long time. Now it is conceivable that another genetic change occurred later that affected brain processes and cannot be read from the fossil bones. However, with this new acquisition, people would have to have displaced all previous Homo sapiens populations in the Old World at lightning speed, and there are no signs of this.
I think it is much more likely that the new ability of H. sapiens lay fallow for a long time. Modern man possessed it from the beginning - or developed it very early - but it was only some kind of cultural impetus that finally activated this capacity. From then on, the new behavior patterns spread quickly, provided that they were beneficial to people. All populations that had the appropriate potential could adopt the behaviors. The cultural contact was sufficient for this. Displacement was not necessary.
We cannot say with certainty what the decisive innovation was. At the moment, most speaks for the language. Language doesn't just serve as a medium for exchanging thoughts and experiences. It forms the basis of thinking. This includes categorizing and naming objects and sensations of the inner and outer world and associating them between the resulting mental symbols. We cannot imagine thinking as we know it without language. Our creativity is based on our ability to create mental symbols. Only the combination of symbolic content enables questions like: "What if ...?"
How a differentiated language once emerged in a Homo sapiens population remains hidden from us, regardless of many linguistic considerations. But the new acquisition certainly helped the owners in their struggle for survival. That these people do not always use their symbolic abilities wisely - the bitter experience was not spared the rest of the world, not even the Neanderthals.
Neanderthals. The dispute about our ancestors. By Ian Tattersall, Birkhäuser, Basel 1999.
Puzzle incarnation. On the trail of human evolution. By Ian Tattersall. Spectrum Academic Publishing House, Heidelberg, Berlin 1997.
Lucy and her children. By Donald Johanson and Blake Edgar. With photographs by David Brill, Spektrum Akademischer Verlag, Heidelberg 1998.
The early days of man. The way to Homo sapiens. By Friedemann Schrenk, C. H. Beck, Munich 19982.
The phylogenetic position of the Neanderthal man. By Winfried Henke and Hartmund Rothe in: Biology in our time, vol. 29, issue 6, pp. 220–329 (1999).
The Origin and Diversification of Language. By Nina G. Jablonski and Leslie C. Aiello (eds.), University of California Press, 1998.
The Human Career: Human Biological and Cultural Origins. By R. G. Klein, University of Chicago Press, 19992.
From: Spectrum of Science 3/2000, page 46
© Spektrum der Wissenschaft Verlagsgesellschaft mbH
This article is included in Spectrum of Science 3/2000
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