There can be only one

No I’m not referring to Highlander I am referring to species of humans. Out of many species that fall under the umbrella term of the genus Homo we are the only one that has survived- Homo sapiens. The mystery behind this has had religious, philosophical and scientific ramifications over the ages that have been debated to this day. But who were these other humans? And can we really consider them to be human?

From the archaeological record we know a fair bit about these other humans which may be able to tell us just how human they were by identifying sociality, intelligence, technology and culture.

Robin Dunbar found a relationship between a part of the brain known as the neo-cortex and theory of mind. Theory of mind refers to a level of sociality- the first level dictates that person A knows something about person B. The second level dictates that person A knows that person B knows something about person C; and so on. Therefore the higher the level, the higher the capacity for an individual to comprehend what a group knows. This type of intelligence becomes important when we start to consider how a group functions within a landscape; they form social bonds which is crucial for group activity. Seeing this hallmark within primates, Robin Dunbar extrapolated the size of the neo-cortex within extinct humans from archaeological remains, and use it to infer upon theory of mind and sociality. What he found was a general clumping of all the extinct Homo species around the Homo sapiens mark. The lineage that led to the genus Homo diverged 6 million years ago from chimpanzees. The first Homo species that appeared on the scene was Homo habilis at 3 million years ago. It is very likely that by then, H. habilis had the intelligence to understand social situations.

While H. habilis was the first Homo species to make and use tools (which led to their alternative and rather informal name Handy Man), Australopithecus afarensis was actually the first species to do so. A. afarensis was an earlier species that walked on legs as opposed to knuckle-walking, and it is possible that the Homo lineage came from this species. The earliest evidence of tool use on bones comes from Ethiopia dated at 3.39 million years ago where it is known that A. afarensis inhabited this region. Clearly by the time of H. habilis, we start to see the beginnings of a rather primitive form of intelligence that enabled them to form social groups and use their own type of technology, which was known as the Oldowan tool industry.

Eugene Dubois, a Dutch palaeo-anthropologist, was in Java (S.E Asia) in 1890 when he found a set of skeletal remains. He had found what was later called Homo erectus. This species was clearly the first member of the Homogenus to have migrated out of Africa. One of the most important finds belonging to this species was Nariokotome Boy found in Kenya in 1984. What was particularly interesting about this find was that the individual was thought to be just a little bit older than 11 years old and, from his remains, it could be seen that he was about 6 foot tall! This is a species that was very well adapted to the hot climate of Africa; H. erectus was tall, gracile and slender with long legs that enabled them to travel for long distances, which ultimately they did.

To perfectly complement how H. erectus was adapted to the hot climate of Africa, H. heidelbergensis illustrates adaptations to a cold climate. Likely to diverged from H. ergaster as well (and thus be a sister group to H. erectus), H. heidelbergensis was the last common ancestor of Neanderthals and modern humans. But it was also the first Homo species to move into Europe. The commonly held theory is that H. heidelbergensis evolved into Neanderthals in Europe. As such Neanderthals appeared to be very well adapted to the cold; they were short, stocky and well-built when compared to the tall and more graceful modern humans.

They had a wide distribution across Europe and Asia; from Israel to Wales, and as far north as Siberia and south as Gibraltar. Vast amounts of archaeology have shown that Neanderthals had their own culture and technology, and existed together in their own social groups. But all good things come to an end. By the time the Neanderthals had settled into their life in Europe, at 60,000 years ago, the climate got severely worse. Before the start of the Ice Age at approximately 28,000 years ago, modern humans had already arrived and settled themselves, and the Neanderthals had become extinct.

The arrival of modern humans into Europe from 50,000 years ago is part of the next hallmark in our evolution: the Upper Palaeolithic Revolution. This revolution saw a cultural explosion. A wide variety of art has been attributed to the Upper Palaeolithic. Such examples include ornaments, figures and cave art, but it also included technology for acquiring and processing food. While the Neanderthals had their own technology for the same reasons, modern humans had a much more diverse toolkit. But as far as we know, no art found has been associated with Neanderthals.

In 2010, DNA analyses suggested that Neanderthals and modern humans interbred just outside of Africa before modern humans spread around the world. Following on from this, a few other studies have suggested that interbreeding was occurring between other human species, such as between H. erectus, and a possible new human species the Denisovans, and between modern humans and the Denisovans. While many more analyses need to be done to confirm this, this claim has immediate implications as to what we consider a species. A species is defined as a group of individuals that can only reproduce with each other. If Neanderthals and modern humans were interbreeding with each other, then this suggests that Neanderthals and modern humans are the same species, and that we (current modern humans) are descended from this interbreeding. More work however needs to be done. Ancient DNA is a field fraught with difficulties but as DNA technology improves we will have more data to look at.

By now we see a picture emerging as what we could consider as “being human”: the capacity for sociality and intelligence, use of technology and the element of culture. At the same time the lines between these various humans are beginning to blur. If the DNA evidence holds up, as more studies are carried out, then perhaps we should start to consider all of these humans under just one species name and designate each one by sub-species. The archaeological evidence certainly suggests that many of these types of humans had a level of intelligence that meant they could establish technology and culture which appears to be just as different from each other as they are morphologically. We are so willing to find the point in time where we can say “here is where we became human!”  The truth is we can’t. We, Homo sapiens, may have arisen around 200,000 years ago, but humanity could have begun much earlier. So when natural selection and bad luck killed off the other types of humans, it left us- the sole human survivor. This then leaves us with just one question:

For how long, in this changing world, can we survive?

For more information:

• Dunbar, R. 2003. The Social Brain: Mind, Language and Society in Evolutionary Perspective. Annual Review of Anthropology 32, 163-181
• Green et al. 2010. A Draft Sequence of the Neandertal Genome. Science 328 (5979) 710-722
• Stringer, C. Andrews, P. 2005. The Complete World of Human Evolution. Thames and Hudson, UK.
• Oppenheimer, S. 2004 Out of Eden. Robinson, London

This article was written to complement the presentation “Ancient Humans: Who were they? And who got it on?” that was given on the 5^th December 2011 for the Natural History Society. For more details on the author, see http://independent.academia.edu/DanaeDodge