Sex and the Single Neanderthal: Interbreeding and Extinction

by John MacBeath Watkins

Svante Pääbo, a palaeogeneticist at the Max Planck Institute in Leipzig, Germany, whose team

sequenced the Neanderthal genome, estimates that human populations outside Africa have a heritage

that is between 1 and 4 percent Neanderthal.

Although Neanderthal existed until about 25,000 years ago, the interbreeding seems to have

happened before modern humans entered Europe about 44,000 years ago. Most likely this

interbreeding happened in the Middle East, where some skeletons have been interpreted as hybrids of

modern humans and Neanderthals. The interbreeding seems to have taken place 50,000 to 100,000

years ago, not during the time modern humans and Neanderthal co-existed in Europe.

That's a curious fact. Usually, if you put two groups of humans in contact with one another,

they hook up. If there was no sexual intercourse, can there have been any social intercourse? I'm

inclined to think not. And if this is so, why was there social (and sexual) intercourse in the Middle

East and not in Europe?

The timing may be a clue. As I noted in my earlier paper, Thoughts on Structuralism and the

Death of “Ghosts:”

About 90,000 years ago, shell jewelry, use of pigments and beautifully crafted tools appeared, signaling the appearance of an advanced Neolithic civilization; there is even some indication of symbolic behavior as far back as 160,000 years ago. These early signs of Upper Paleolithic culture disappeared, reappearing several times before civilization “took” permanently (one hopes) about 45,000 years ago. Adam Powell, Stephen Shennan and Mark Thomas of University College, London1 theorize that the repeated disappearance of cultures is related to declines in population. In other words, the structure of thought behind early Neolithic civilization required more minds than existed following

1 Late Pleistocene Demography and the Appearance of Modern Human Behavior

Powell et al.Science 5 June 2009: 1298-1301DOI: 10.1126/science.1170165

droughts or other disasters that reduced population below a level that would sustain it.

Note that 70,000 years ago, the Neanderthal and modern human populations would have been

technologically equivalent, neither able to sustain a larger population from the same environmental

resources. This implies that they would meet in groups of roughly equal numbers and possess roughly

equal power if they came into conflict.

At the point where modern humans entered Europe, however, these conditions no longer

applied. Neanderthal populations would have still been using about the same technology as they were

70,000 years ago. Upper Paleolithic culture gave modern humans better tools, allowing them to make

better clothing, trap a wider variety of animals and use more of the food sources available in the

environment. This would have allowed them to support larger populations in the same territory

Neanderthal occupied. In case of conflict, they would be the more powerful group. In the absence of

conflict, they would use the resources the Neanderthal needed to survive, and still have other food

sources to fall back on. The Neanderthal relied on ambush hunting of large game. If the large game

was gone, and the modern humans were still there, living on smaller game and plant resources, the

Neanderthal would be starved off the land. The only way to prevent that would be to adopt the culture

of the invaders.

Why did this not happen? Did the invaders bring with them diseases the Neanderthal couldn't

cope with? It's possible as a contributing cause, but modern humans coexisted with them in Europe for

about 10,000 years, so there was no sudden mass extinction. That's a long time to go without having

sex with a neighboring tribe. It's possible we'll eventually find evidence of later interbreeding, but the

current evidence provides a puzzle. Were the cultures so different that it made interaction unthinkable?

What could cause that?

In the settlement of the Americas, those areas north of Mexico saw indigenous populations

largely supplanted, while in Latin America there was extensive interbreeding. In the US and Canada,

the European invaders had farming technology that allowed them to support larger communities on a

given piece of land than the Native Americans. In most of Latin America, farming was sufficiently

advanced that European methods of agriculture could not support larger populations, and in those areas

the indigenous population was not supplanted. Instead, the invaders adopted the crops grown by the

people already on the land and intermarried with them, a situation analogous to the encounter between

Neanderthal and modern man in the Middle East.

In the US and Canada, there was less interbreeding, and it is possible for people whose

ancestors have been in those countries to have no Native blood, a fact that seems nearly as odd as the

lack of interbreeding between Neanderthal and modern man in Europe. As we advance deeper into the

future, however, it seems all occupants of North America are likely to show signs of interbreeding.

After 35,000 years, pretty much everybody living on a continent is related to everybody else. For there

to be no signs of interbreeding during the European encounter with Neanderthal, something even more

calamitous had to happen to Neanderthal than happened to North American Indians.

It seems only possible if the difference in culture was so vast that those with Upper Paleolithic

culture did not view those without this culture as the same kind of creature. We've seen something like

this happen when Europeans came into contact with Neolithic people. Among the worst examples was

the treatment of Tasmanian aborigines. They were hunted like animals and many who did not die

through armed conflict died of introduced diseases. They were driven to the edge of extinction without

any appreciable interbreeding primarily because the European settlers did not truly view them as

human.

It's my belief that human nature 35,000 years ago was much as it is now, with the same

shameful flaws and redeeming glories. Our ancestors were as capable of cultural arrogance as we are.

The complexity of tools produced by a culture is not the only measure of whether they have reached

Upper Paleolithic culture. One primary distinction is evidence of symbolic thought.

Symbolic thought can give people a strong sense of who they are, who is inside the group and

who is outside. European settlers in Tasmania were distinguished from its aboriginal occupants by

language, dress, religion, written communication (and on the part of the aboriginal culture, lack

thereof,) culture in general, the sophistication of their tools and their physical appearance. With the

exception of written communication, all of these things would be true of the meeting between modern

humans and Neanderthal 35,000 years ago. In all likelihood, the settlement of Europe took substantial

time and involved waves of immigrants. It was a period of climatic instability that would have

challenged all European populations, and each time cold or flooding or drought reduced the

population, more modern humans were waiting to come in when things got better. Each wave would

have brought new diseases, as discussed in The “Neanderthal Enigma" and the Structure of Thought.

Just as the aboriginal Tasmanians were more susceptible to imported diseases than the European

settlers, the Neanderthal would have been more susceptible than the modern humans moving in on

their turf.

Ferdinand de Saussure, whose A Course in General Linguistics revolutionized the way people

thought about language, argued that each language creates its own reality. Words do not just represent

the thing they stand for, they distinguish that meaning from those represented by other words. In so

doing, language gives us the categories we use for abstract thought.

Now consider the category of race. The word does not always refer to appearance or any other

readily detectable difference. Some Jews were able to live under the noses of the Nazis, provided they

had the right papers, because they looked no different from most Germans. Race is a social

construction whose meaning, in the case of relationships between people who have decided they are of

different races, is about social difference. In language, the word we assign to a meaning is the sign,

and the meaning is what is signified. To the extent that the category of a specific race is connected to

visual differences such as color or facial features, these are signs; the meaning of that category of race

is the signified. When modern humans and Neanderthal met 70,000 years ago, their culture was at the

same technological, and presumably cultural, level of complexity. They would have interacted as

equals and interbred. When they met again 45,000 years ago, modern humans had made the leap to

upper Paleolithic culture, giving them a more complex set of skills and changing their sense of who

they were in relation to the Neanderthal. The situation might have been similar to that of European

settlers coming upon the Tasmanian aborigines.

Tasmanian aborigines seem to have lost some skills when the sea rose 10,000 years ago, cutting

Tasmania off from the rest of Australia. Unable to renew their skills through trade, intermarriage with

other tribes or exchanges of information, they would have been dependent on the population of

Tasmania for what skills could be maintained. If in one generation all those who knew how to make

bone needles died, there would be no one from whom to learn the skill.

The Tasmanians began to have contact with Europeans in the late 1700s, and would have been

exposed increasingly to imported diseases, increasing the likelihood of the disappearance of cultural

capitol. Similarly, a disparity in power and a cultural gulf could have been enough for Upper

Paleolithic modern humans to treat Neanderthal very differently than earlier modern humans (who had

been on the same cultural level as Neanderthal) had treated them in the Middle East 70,000 years ago.

Just as European settlers treated Tasmanian aborigines as “not us,” not even human, Upper Paleolithic

modern humans may have felt a similar gulf between themselves and Neanderthal who did not possess

their level of symbolic thought. The results, for the European aboriginal population, could have been

as tragic as it was for the Tasmanian aboriginal population.

Modern humans are now considered to have reached their current form about 150,000 years

ago. Most of Eurasia and Africa would have been occupied by human populations capable of

interbreeding with modern humans. Although Neanderthal is the most widely known of these

populations, others such as Rhodesia Man, dated to between 125,000 and 300,000 years ago, lived in

regions modern humans later settled in. It would be interesting to know whether there was

interbreeding with other indigenous populations modern humans encountered as they spread, and

whether interbreeding continued after they achieved Upper Paleolithic culture. It is an enquiry that

could provide interesting and disquieting information about human nature.