Marija Gimbuta’s Kurgan theory (or more precisely, its renewed version) of the origins of Indo-European languages is today widely accepted. Archeogenetics solved this long lasting question, which remained unsettled as long as the only tools were linguistics and archeology. There was a major migration of steppe people to Europe, the DNA of Corded Ware people does have a large component from steppe people, like Yamnaya. The emergence ot R1b and R1a Y-DNA haplogroups in Europe was caused by the migrations of steppe people to Europe.
In the book Archeology and Language, The Puzzle of Indo-European Origins (1987) Colin Renfrew proposed a competing theory, according to which Indo-European languages were spread to Europe, and even to India, by Neolithic farmers around 6000 years ago.
Today we know that this Anatolian origin theory by is incorrect, but the arguments that Renfrew presents in this book are still very valid and need to be answered. In the book Renfrew tells that he read The Aryans (1926) by Gordon Childe, an early theory placing the homeland of Indo-Europeans to south Russian, as it is in the Kurgan theory. After reading the book Renfrew noticed a number of problems which inspired him to write Archeology and Language. While not being an eminent archeologist like Renfrew, in fact not eminent in anything, I did notice a number of answers to these problems while rereading Archeology and Language this week. There was 1987-1926=61 years between Childe and Renfrew and there is only 2019-1987=32 years between Renfrew and this my post, but maybe it suffices for reconsideration of the ideas. After all, since Renfrew’s book we have the DNA results.
I will not go to the DNA at all, as Renfrew did not have this possibility and his arguments are on a quite different direction. Let us say that the steppe theory is rather correct and it can be taken as the starting point.
Renfrew posed the following very good arguments:
1) What advantage did the migrating Kurgan people have over the existing farming communities? He sees the advantage of farming over hunter-gatherers: farming could support a population of 5 people in a square kilometer, while hunter-gatherer population density was about 0.1 persons in a square kilometer. Thus, advance of farming would replace the population in much of Europe and lead to a language change. But Renfrew does not think that a horse and a wheel could give such an advantage to pastoral Kurgan people. According to him, mounted warriors were a much later invention and around 3000 BC steppe people could not fight on horseback. This argument is not strong: horse was most probably domesticated around 3500 BC by the steppe people and it was used in warfare in some way (which does not necessarily imply that warriors fought on horseback, they could move fast in horse-pulled wagons or sledges).
2) Why did the Kurgan migrations happen and why did they happen in this time? That is, what was the reason these people migrated and why did they not migrate earlier? Concerning India this can be answered: the 4.2 ky event (aridation) caused the collapse of Indus civilization. Indo-European invaders used this opportunity. But the question is valid in Europe: Corded Ware is dated to 2,900-2.300 BC and there was no climatic change at this time. Thus, why did the steppe people migrate and just at this time?
3) Why should Kurgan migration have caused a language change? Was it elite domination, as was the case with Magyars around 900 AD? Today we know it was not elite domination, it was a mass migration of steppe people, and mostly by men.
Renfrew refers to a model which apparently claims that combining the logistic curve for population growth with a random walk for short distance migrations of small tribal units leads to a constant 1 km per year advance of the populated area. He takes this as the model for the advance of agriculture in Europe. In this model the birth rate is initially 3.9% and then drops to a small value following the logistic curve. Renfrew says that in this model the population is doubling every 17 years. The driving force is the ability of agriculture to support 50 times as many people as hunting and gathering.
I do not accept this model at all. If the population is doubling in whatever number of years, it grows exponentially. If the population density in the settled area stays constant, then the area doubles with the same speed as the population and the radius of the settled area grows with the square root of this speed, that is, also exponentially. The model cannot give a constant rate of advance of 1 km per year.
The speed 1 km per year corresponds to the advance of American Indian population in the Americas from archeological data and is probably taken from there. What is known of American Indians is that they had constant tribal wars. Therefore we can assume that inside the settled area tribal war reduces the population growth to zero. There is population growth only in the border area, which has the length of 2πr, assuming that the radius of the settled area is r, and some width Δr. If the population doubles in the time T, then the area doubles in this time from 2πr∙Δr to 2πr∙2Δr. The radius grows from r to r+Δr in the time T. We can estimate the doubling time. In average a woman gives birth to 6 children unless some prevention is used. About half of them die before reaching maturity. Thus, two people (a man and a woman) give birth to three adults to the next generation. A woman generation is about 29 years. Thus, the doubling time is T=(ln 2/ln (3/2))∙29 years = 49.6 years, about 50 years. If the doubling time is 50 years, and the settlement advances 1 km in a year, then Δr=50 km. This is a fairly reasonable width for the border area where the population can grow as new area can be taken. This, I think, is a much more reasonable model.
The population doubling time of 50 years is therefore a value when there is no selection (apart of the internal selection that mating is not quite random in a population, but such selection there is in every population: the rich tend to marry the rich, the clever tend to marry the clever, and so on). In the American Indian society there was very strong selection of men because the population growth inside the settled area must have been zero. This implies that of the three adults that one couple would naturally manage to grow to maturity, one would die because of tribal warfare. As only males excel in warfare, this selection picks up strong and clever males. It may also select women for beauty, as beauty would be the criteria why to leave a woman alive in warfare.
The spread of agriculture in Europe from 6000 BC to 3000 BC must have faced a similar problem of population growth. Agriculture could support 50 times as many people as hunting and gathering, thus hunter-gatherers would have to withdraw or adopt agriculture (both of these ways were used), but the population growth problem is inside the farmer population: the population can grow only in the border area. The solution may have been constant tribal warfare, as in the case of American Indians, or it may have been one of the ways of stopping population growth.
In hunter-gatherer societies population does not grow. Some hunter-gatherer societies are very violent and on constant warfare with neighboring tribes, but more typically the zero population growth is a result of prolonged breast feeding and infanticide. Most hunter-gatherer tribes must keep moving with animal herds and find ripening plants. A woman cannot carry more than one child. Thus, the number of children must be limited and the population growth is stopped. When the reason for infanticide is movement, it will affect moth boys and girls. If the living conditions are difficult, mostly girls are killed, but men die often in hunting.
In an agricultural society there is no need for infanticide because of movement. If the population growth must be stopped (as it must be, else the result is hunger), children of both sexes could be killed, but there is a difference. Killing girls creates a group of men without women and such a group will challenge the men who have women. Killing boys does not have this problem, and agriculture my nature falls to the gathering profession, belonging more to women. Thus, most probably boys were killed and the society had wide scale polygamy. This seems to have been the case in Europe: Y-DNA diversity dropped drastically after the beginning of agriculture, while mtDNA diversity did not drop. The small diversity of Y-DNA seems to have caused a mutational overload and collapse of many early farmer societies in Europe. Other results would be taming of the men in such a society, and the low ability of such societies to resist invaders. But the solution would give peace for some time.
The time such a peace would last, would be determined by the time it takes for the settled area to reach the ultimate borders. In Europe this time was around 3,500 BC. In Eastern Europe the farmers would stop to the steppes, which did not suit to farming with the old methods. In these steppes lived Eastern European Hunter-Gatherers. Some of these hunter-gatherers, merged with Caucasian Hunter-Gatherers and some Neolithic farmers, developed a new life style: animal herding. As Colin Renfrew correctly notices, pastoral people are in a sense dependent on agriculture as they get much of their food from agriculture, either by growing themselves or by trading. Thus, the pastoral life style developed as a new invention as a result of agriculture reaching the borders of the steppe.
In the beginning animals were wild and as hunting was a male profession, animal herding was more of a male profession. If any children should have been killed by these people for stopping the population growth, it would have been girls. This implies that the tribes would be in constant war with neighboring tribes, as was the case with American Indians. Rather soon they tamed the horse and developed metallurgy, making these tribes quite dangerous in a military sense. The new pastoral life style spread again maybe 1 km per year over the steppe, but finally borders were reached. Assuming that the area was some 600 km times 1000 km, it would take about 1000 years to reach the borders. Animal farming should have supported at least 1 person per square kilometer, thus there would be 0.6 million steppe people. Each generation they would produce 150,000 men, who did not inherit anything, as the oldest son inherited everything, and they would not have had enough women. Around 3000 BC they would turn to the only natural direction: from the Black Sea thorough Ukraine and Poland to the North Sea. There they would spread to both directions as the Corded Ware people. The farming societies, having too few men, could not resist.
Now, to answer Renfrew’s questions: The main advantage these Kurgan people had was the large number of warrior men, who had trained warfare in the steppe, who had the horse, the wheel and the battle axe. The migrations happened when the steppe was all populated by animal herders and population growth forced them to look for other living space. The new polar star, Thuban (almost exactly at the North Pole in 2700 BC and usable as a Pole star about 1000 years to both directions), may have inspired the conquest of new lands. There is maybe some lesson to be learned from Kurgan migrations. The main problem is population growth. For some time Europeans solved the population growth by moving to the America and other colonies. Today the solution is reduced birth rate, but it reducers the number of men as well as women. Therefore, male selection is not a force as it once was. Probably male selection was the driving force for increased intelligence, which then will not continue. Instead, sperm quality will decrease, as male selection also kept male fitness up. The population will become tamed, lose intelligence, lose fertility. Finally it will be destroyed by some warriors, but probably not in the next one thousand years, so let us enjoy the peace as long as it lasts. There was once a different solution for reducing the birth rate than what there is now: in Christianity and in Buddhism a sizable fraction of men become monks. This voluntary celibate had the advantage that is was selective: it selected the more peaceful men, thus the warrior men remained and kept the population competitive. Well, those times are gone. Now we just wait for the collapse.