How are we related to the Neanderthals? When did our ancestors become bipedal? Which species was discovered only via fossil DNA? The history of the human species becomes more and more complex the more evidence concerning it accumulates.
In 1856, during limestone mining in the Neander valley near Dusseldorf, Germany, workers came across some bones which they thought belonged to a bear. The quarrymen invited a local teacher and natural historian, Johann Carl Fuhlrott, who examined the remnants and immediately recognized them as human remains. However, the longer they were examined, the clearer it became that the bones could not have belonged to modern humans. The people who lived in the valley belonged to a separate population, perhaps even a separate species – very close to modern humans, but significantly different. More and more bones of this species were uncovered over the years, in Europe, the Middle East as well as in Asia. They were all given the name Neanderthals, Homo neanderthalensis, or “men of the Neander valley", after the location in which the first bones were originally discovered. Thus, interestingly, the study of ancient human species and of the evolution of modern humans, Homo sapiens, preceded the first publication of the theory of evolution by natural selection by two years.
The next major finding was uncovered about 35 years later, on the Indonesian island of Java. Darwin’s theory was already known and accepted in the scientific world, and the Dutch researcher Eugène Dubois set out for Asia with the expressed goal of finding early human fossils, which were predicted to exist by the new theory. Why did he choose to go specifically there? He reasoned that the orangutans and gibbons living in Southeast Asia must be man’s closest animal relatives, and thus that evidence on human evolution must be found in that region. Dubois indeed found a partial skull, larger than that of a chimpanzee but smaller than that of a modern human. Two years later he also found a femur bone that suggested that these ancient individuals walked upright on two legs, which was why the species was given the Latin name: Pithecanthropus erectus, “upright human ape”. Later, the species was defined as part of the Homo genus and was reclassified as Homo erectus, meaning “upright man”. We know today that Homo erectus appeared about 1.9 million years ago and became extinct about 140 thousand years ago, and that he wasn’t the first bipedal species, but rather the first bipedal species discovered.
Dubois found the bones he was looking for, but was wrong about his premise: humans did not develop in South Asia. The great apes that can be considered our closest relatives, as Darwin had suggested 150 years ago, and as modern genetics have since confirmed, are actually the African ape species: the chimpanzee, the bonobo and the gorilla. Many fossils of hominins, more ancient yet than Homo erectus, were found on this continent in the 20th century and the theory accepted today sees Africa as the cradle of humanity. How did modern humans develop from their ape-like ancestors? When did they start walking on two legs and making tools? These questions, as well as many others, remain unanswered.
Fascinating finding, wrong conclusions. Dubois (standing center) with researchers at Cambridge University. Source | Science Photo Library
In order to understand the confusing history of the human race, we must first understand what is missing in it. There is, unfortunately, no orderly chain linking one species that existed for a while, became extinct and gave way to another, more advanced “human” species, which in turn repeated this chain of events, eventually reaching today's modern humans. The familiar image of human evolution, in which we see a chimpanzee-like creature on one side, while on the other we find modern humans with a series of individuals found between then, each more upright and a bit less hairy than the one before him, is an abstraction that falls short of properly describing a very complex process.
What we do have instead are bones and bone fragments that belong to about 20 different species, the precise number of which is also under debate. Some researchers may think that three fossils found in relatively close proximity could belong to the same species, while others will argue that each one represents a separate species. More and more fossils are continually being uncovered: one of the last found fossils, Homo naledi, was first described in the scientific literature in late 2015. Many of the species co-existed over tens and hundreds of thousands of years. In fact, it appears that the current situation, in which only a single species of humans lives on Earth, is the exception.
Some of these species were quite similar to ourselves, while some looked more similar to chimpanzees. Among them were some with smaller and some with larger brains, some species were bipedal and some appear to have spent a large part of their time on trees. We can arrange them into groups according to their features, and use different dating methods to determine which appeared earlier or later, but we have no way of knowing which of them were our direct ancestors, and which represented merely a “side branch” in our family tree.
The Descent From The Trees
These are followed by the Australopithecus,“southern great ape”, a genus that included a number of species that lived from about four million until about two million years ago. The most complete as well as the most widely-known fossil in this group is a skeleton of a young female who was named “Lucy”, after the Beatles’ song “Lucy in the Sky With Diamonds”, which was being played loudly on a tape recorder at the researchers camp on the day of the skeleton’s discovery. About 40 percent of Lucy’s skeleton was found, and thanks to it as well as to other fossils, we now know quite a bit about Lucy and her kind. Their features were, as we would expect, a combination of human-like and ape-like characteristics. They were bipedal, but their brains weren’t much larger than those of a chimpanzee, and their faces were very much ape-like, with a protruding jaw and no chin. They were small in stature, and were not much taller than the Ardipithecus that preceded them. Different species of Australopithecus have been discovered in East Africa and in Southern Africa.
The genus of Paranthropus, “beside humans”, appeared about 2.7 million years ago and may have evolved from one of the Australopithecus species. They had a strong and muscular jaw and wide teeth, likely adapted to eating fibrous plants and seeds. As their name suggests, we know with near certainty that the Paranthropus are not found in our direct lineage, but rather represent a side branch. The later species did not exhibit the special characteristics of this species, and thus it appears that they disappeared without leaving a trace.
Bipedal, but with a brain similar to that of a chimpanzee. Illustration of an African Australopithecus | Source: Science Photo Library
The First Humans
Now we arrive back to our genus – Homo. The main feature of members of the Homo genus is their larger brain. The earliest known Homo species was Homo habilis, who appeared more than two million years ago. The meaning of the name is “handy man”, since chiseled stone tools were discovered alongside its fossils. However, in recent years more and more evidence is accumulating to suggest that Homo habilis was not the first hominid to use tools, and that some members of the Australopithecus species used them as well, despite having small brains. Given that chimpanzees and other apes use simple tools, this may not come as much of a surprise.
The size of Homo habilis’ brain was less than half that of a modern human, but was still larger than that of the Australopithecus. Homo erectus, who appeared after him, had an even larger brain. Homo erectus is the first species we know to have left Africa and settled in the Middle East and across Asia, where Dubois found the first bones of this species. One of the earliest and most investigated sites in which a Homo erectus population lived is Gesher Benot Ya'aqov in Israel. Based on findings at this site, we now know that Homo erectus used fire, already 780 thousand years ago. Their tools were more complex and diverse than those of Homo habilis, and included stones chiseled into a double-edged serrated blade.
Unlike Homo erectus, who developed in Africa and left it, the Neanderthals, as far as we can determine, never set foot on the continent. They developed outside of Africa, perhaps from a population of Homo erectus, and lived in Europe and in Asia. Besides the Neander valley after which they were named, these fossils were found in many sites, from Portugal to Siberia, including some sites in Israel: The Tabun cave in the Carmel, the Amud Cave and others. They first appeared about 400 thousand years ago, and disappeared about thirty or forty thousand years ago, not long after modern humans had left Africa. The abundance of fossils we have from this species, made the Neanderthals the human species that we know most about, besides ourselves of course.
Judging by their appearance, Neanderthals weren’t very different from us. Their bodies were somewhat tubby, their arms and legs were shorter, but the main differences between us and them seem to be in the facial area: they had a prominent brow ridge, a large nose that was placed higher on the face, compared to modern man, while their chin was especially small. They seem to have been been stronger than modern humans, and, in contrast to the belief that they were more primitive and less intelligent, their brain was slightly larger than that of Homo sapiens.
Neanderthals had a developed culture. They wore clothes, although it seems they did not know how to sew per se, but rather tied skins and furs around their bodies, and also created jewellery. They also built complex structures, some of which may have been used for conducting ceremonies, and it appears they buried their dead. New research even claims that the Neanderthals beat modern humans to the Americas, but this claim has so far not been widely accepted by the scientific community.
We still do not know why they became extinct. The coincidence between the timing of Homo sapiens, or modern humans, leaving Africa, and the disappearance of the Neanderthals only a few thousand years later is suspicious, and many researchers suggested that our ancestors killed their relatives causing their extinction. Today, however, the common belief is that Homo sapiens may have supplanted the Neanderthals by competing for food sources and taking over territories, but that actual fighting was not common.
The reason behind this assumption is that despite the many uncovered fossils, no evidence of such a struggle was found at any site from the period in question. Recently, as new and sophisticated tool of genetic analysis have entered the field of human evolution, it has become clear that if there was indeed contact between the populations, at least in some cases it did not lead to death, but rather to new life.
Slightly larger brains than modern humans, and stronger, but extinct. An illustration of the Neanderthal man | Source: Science Photo Library
Stone Age Genetics
The study of man’s evolution has become more advanced over the years: the fossils were examined with state-of-the-art tools, from x-rays to micro-CT (computerized micro-tomography). Still, at the end of the day, it consisted mainly of the meticulous examination of bones and their comparison to other bones, either fossilized or modern. And then came DNA.
In recent years, sophisticated methods have been developed for the extraction of genetic material from samples that can be hundreds, thousands and even tens of thousands of years old. A new research field, ancient DNA research, was born. There is however, a limit as to how ancient a fossil can be, before its genetic material becomes completely degraded. Research has shown that the half-life of DNA is about 521 years (meaning that after this time period, half the amount of DNA is degraded), and it becomes completely unreadable after about a million years and a half. However, even long before that time, in practice - the older the specimen, the less useful the genetic material found within it.
Nonetheless, this time window leaves us with quite a few fossils, from which DNA can be extracted for research. Today, the majority of fossil DNA that we have available is Neanderthal DNA, the analysis of which has revealed a rather sensational fact: most humans living today carry genetic material originating from this group of ancient humans. Genomic analysis has revealed that the genome of nearly every living person outside of Africa contains between one and five percent Neanderthal DNA.
However, no genetic material originating from the Neanderthals can be found in people of African ancestry, and the likely reason for this is that the gene exchange between the two species took place after the migration of individuals of our species away from their continent of origin, to Asia and Europe. There, they likely encountered Neanderthal individuals, who, as already mentioned, never lived in Africa, with some of these encounters ending in shared offspring. This gene flow apparently was not one sided: a study has shown that Neanderthals also received some of their DNA from Homo sapiens.
The possibility of analyzing fossil DNA allows us to learn about various practices of the Neanderthals, such as their food customs. In a recent study, researchers have extracted genetic material from the dental plaque - a white layer of biofilm found on teeth - of Neanderthals from Belgium and Spain. The Belgian plaque revealed the presence of DNA from a wooly rhinoceros, wild sheep and mushrooms, while it appeared that the Spanish Neanderthals ate mostly plant food, as evidenced by pine nuts and moss found on their teeth.
Along with plant DNA, researchers also found DNA from archaea, a single cell organism that also resides in the oral cavity of modern humans. Comparison of the genetic makeup of the archaeal species typically found in the modern oral cavity to that found in the Neanderthal dental plaque, revealed that their lineages separated only recently, long after the genomic divergence of the lineages leading to Neanderthals and to modern humans. This implies that at some point, archaea residing in the oral cavity were transferred between modern humans and Neanderthals. Naturally, we do not know how this happened, but it’s nice to form romantic speculations about lovers from different species sharing kisses, Romeo and Juliet of the stone age.
The biggest surprise that fossil DNA has revealed was a new species of man that could not have been discovered by any other method. In 2010, Genetic analysis of a bone fragment found in 2008 in a cave in the Altai Mountains in southern Siberia led to the identification of a new hominin group - the Denisovan man, or Denisova hominins - a population with a different genetic makeup than that of Homo neanderthalensis, who apparently also lived in this area. Three more teeth, belonging to this ancient hominin group, have been found since then.
Three teeth and a piece of bone don’t provide us with much phenotypic data, and in fact, everything we know about the Denisovans was inferred from analysis of their DNA. One of the interesting first things to be discovered was that modern humans also shared offspring with this population: Denisovan gene variants were found in modern humans from East Asia and America. Interestingly, one such gene variant, which was found to be especially common in the Inuit population of Greenland, could potentially help Inuits adapt to the cold by promoting heat-generating brown body fat.
A few teeth and a piece of bone. Examining findings from the Denisova Cave in Siberia | Photo: Science Photo Library
Completing the Puzzle
The study of the origin of man, similar to any field that relies on fossils, is largely at the mercy of fate: the majority of animals die and disappear without leaving a trace, and for the reconstruction of species, genera and families all we are left with are a few broken bones that were preserved during the long period of time between their death and their discovery by researchers. The result is a puzzle in which vast areas are missing, and scientists often disagree as to where to embed the few pieces we do have.
In this article we have focused on the main known groups of ancient humans. It is much less clear, however, how many of the other species that existed fit into the picture. We did not mention, for example, Homo floresiensis, a particularly small species of human, dubbed “The Hobbit”, who lived on an island in Indonesia, despite the fact that a 2017 study found that Homo floresiensis likely shared a common ancestor with Homo habilis, who by all accounts lived only in Africa.
Scientific theories undergo constant changes and updates in accordance with new findings. Two studies published in 2017, suggested that the split between the lineage leading to the chimpanzee and our own lineage occurred in Southern Europe rather than in Africa, and that the last common ancestor of great apes and humans actually lived there. Very early footprints with human attributes found in Crete may support this claim, which was extensively criticized by most of the scientific community.
Recently, Israeli researchers reported having uncovered a partial skull and a lower jaw, belonging to a new type of prehistoric human, near the town of Ramla, Israel. Puzzlingly, the fossils exhibited properties of both Neanderthals and Homo sapiens but belonged to neither of these groups. The researchers suggest that this individual may have formed part of an ancient population of early humans in the Middle East, which was ancestral to the Neanderthals in Europe, thus potentially providing a solution to many Neanderthal-related puzzles. As often happens in science, these findings have sparked controversy and were challenged by another pair of Israeli researchers who argued that the fossils belonged to a well known Neanderthal population and should be classified as such.
Each newly found fossil, each genetic study and each new method of fossil examination, provide us with yet another piece of the puzzle of the origin of man, and sometimes shed new light on existing parts of this puzzle. Although the picture is far from complete, its outline is already visible - the fruits of the efforts of many researchers for over a century. It is no wonder that this research area attracts so many people, professional researchers and amateurs alike. The question it addresses is one of the deepest scientific questions: where did we come from, and how did we arrive at where we are today.