Throughout prehistoric, written, and recent history, human warfare has been commonplace. Nearly all societies engage in regular or periodic war. In many examples, human warfare has characteristics similar to chimpanzee war: an in-group fights with and kills members of the out-group. This information is not to be misinterpreted as either justifying human violence or considering it inevitable. When it comes to births and fecundity, though, humans are very different from the other great apes. Chimpanzees reproduce once every five to eight years; humans can give birth again within 18 months. It is likely that an increase in male contribution to child rearing allowed this greater fecundity.
Diamond, Jared. "Sex and the Female Agenda." Discover (September 1993), pp. 86-93
Lidz, Theodore and Ruth W. Lidz. Oedipus in the Stone Age: A Psychoanalytic Study of Masculinization in Papua New Guinea, pp. 27-37 and 51-59
Keeley, Lawrence. War before Civilization: The Myth of the Peaceful Savage, chapter 2
January 20, 2009
Professor Robert Wyman: Now I've been describing the intimate relationship between sex and violence within the chimpanzee social system. This lecture, and forever after, we shift our focus to humans, and we want to ask what's stayed pretty much the same and what has changed. Today I'm going to discuss two topics, one: war in humans which hasn't changed all that much, you can certainly see a continuity. Then I'm going to talk about fecundity in humans, how many children we bear compared to chimpanzees and you'll see there's a very big difference there.
The most obvious similarity and one that gets the public quite excited is the similarity in--violent death has always been very important aspect for humans especially--well all the time, but I'm going to talk now about what's called 'primitive times,' and this is data from a tribe that's in Paraguay in South America in the period just before it had real contact with Western people. So it has nothing to do with modernity; this is apparently the way they lived for time immemorial.
What this table does is list the number of deaths by age, putting them in different age groups. Here are just children or we would call them infants almost, 0 to 3 years. You can notice there's a significant amount of death; this is all illnesses; that's communicable diseases and all kinds of other diseases; that's the percentage of deaths from that, and then there's other causes: congenital, degenerative, accidents some, but here's violence--various forms of violence. 56% of infants from 0 to 3 died because of violence. Here is children age 4 to 14 and again we see that all illnesses, about 15%, accidents. Violence 74%. Now adults during--this is a 45 year period, the number of years in the periods are not equal, and here is illness 28%, not insignificant; accident, not insignificant, but the various forms of violent deaths: 46%, and it's only when you get over 60 years of age--so in each of those three age categories violent deaths have been the dominant form of death. It's separated by males and females, males/females total, and that's true for males and for females, I'm showing you the sum totals. It's only even after age 60 violent death is still the dominant cause, a third of deaths, but it's the only age at which it isn't -- at least half of the deaths, only when you get that old.
It's quite striking how significant violent death is in human demography. Several things should be noticed there, that communicable diseases are less important for hunter/gatherers; these are very primitive hunter/gatherers, the Ache. One of your readings is from their own description of the way they live and the dangers that they face--that communicable diseases are less important because the population density is so low. Later we'll see--and so diseases just don't get to pass around. We'll see later that the influence of diseases rises drastically, especially among infants, when the population density gets high enough so that people pass around--disease is quite common.
Another thing you may notice from this, that more individuals die in the first 3 years of infancy, 131 deaths than in the 45 years of adulthood 126 deaths. So deaths in infancy are 50--per year are 15 times as common as deaths in adulthood. Of 383 people who are cataloged here, only seven people died of old age. All of them had other really identifiable causes. Given this background of the significance of violence, and this includes more than just war, but does not include deaths from animals--being eaten by animals which is considered an accident.
Defining war, going back to--we talked a lot about chimp--you might call chimp war and now talk about human wars, let's take a definition of war as the intentional killing of members of one group by members of another group. The killing is done because they are members of a group not because of any prior or particular conflict between individuals. It's a group thing that determines that the two sides that they're going to kill each other.
The human social system in primitive times and in some politically correct circles, you're not supposed to use the word 'primitive,' but I use it in its original sense of living closer to the way humans did millions--thousands--many thousands or millions of years ago. It's an early form of being human. During that time we lived in small tribal groups and they're multi-male groups, (again we talked about most mammal's solitary males) with strong male bonding, competition for status, lots of inter-group conflict, competition for females and violence against females. Everything that we know says that humans have lived in communities with those characteristics since as far back as we can -- know, and that is the same description you would apply to chimpanzees.
The archeological data shows that through early farming times we lived in these small dispersed settlements, and the average size seemed to be in the same range as current chimpanzees, about 40 individuals. Size of communities range but when you dig up these--the archeologists dig up these old settlement they're in that ballpark. The anthropologists studying currently alive people again find that the smallest organized group of humans is a politically autonomous group consisting of 20 to 50 individuals with a head man. They call this--the proper anthropological term is a band, again, basically the same size as a chimp community.
Among chimpanzees, as I've described to you, inter-group violence is a hit-and-run affair. With a small group of chimps from one community, patrol their boundary; they detect an isolated individual, a very small group, or even better, a single individual in another community, and then they attack. Anthropologists tell us that primitive warfare has exactly the same characteristics. Among current primitive groups the commonest form of combat is called raids and ambushes, and communities are constantly engaging in this hit and run--these hit and run raids on each other and they spring ambushes to catch lone members of the other group.
I lived for a while among headhunters in Borneo. Presumably they weren't headhunters anymore at that time, and it was perfectly acceptable for them to go out and find a child from a neighboring community--same tribe, same everything, but the neighboring community--playing by the river, catch him and take off his skull and they had their attics--were decorated with skulls. None of this was big--that whole community fighting that whole community, but little raids finding individuals, didn't matter if it was child, adult, nothing mattered like that.
You can draw many similarities between the chimp organization of this lethal raiding and human warfare. How does one think about this? Well there are two possibilities. Either whatever you think of the chimp warfare and the causes of it you have to think that a lot of that is still causing human warfare, or you can say as many utopians do, that they're different. That human--human warfare has nothing to do with chimp warfare.
One of the ways to prove or disprove that would be to look in history, as far as we can tell, and if it has different causes, what you have to assume is, we know for sure that this is what chimps do, and we presume that their ancestors some millions of years ago before we split--did that, but we don't really know that, but we presume it's true that chimps did that and then sometime in human history we have to find a period where we stopped doing it. Then at a later period we started doing it again but now for a totally different set of reasons than for the chimp reasons. The strategy of trying to figure out this question is then to go back in history and gather the archaeological and the anthropological--whatever data we can gather, and try to find out: has there been a period in human history where we were not--did not have this inter-communal violence.
The people who believe that war has different causes -- they think agriculture started it because land becomes valuable or private property of some sort, people wanted to get each other's private property, or governments, modern state governments, or very commonly you'll hear that it has something to do with modernity, that civilization has somehow corrupted the pure nature of early humans who were wonderful human beings and didn't go to war.
What was the situation for prehistoric humans? We can go back to the Neanderthals, which are a sister subspecies, and these guys as you know--heavy musculature, robust bones--they were obviously strong characters. When you take--study their graveyards, 40% of Neanderthal skeletons have head injuries. How does one attribute that? Either they were very clumsy and accident prone and always somehow managed to fall on their head--so far as we know they didn't climb trees very much and hang upside down and fall, or there was a lot of club wielding and head bashing going on.
Homo sapiens, not Neanderthals, the earliest human burials that haven't just decayed away are about 20,000 to 35,000 years ago and when you dig them up what do you find? Spear points embedded in the bones, cranial fractures, scalping marks, and so forth. These burial grounds are found wherever archeologists look. Some of the most prominent ones are Italy, France, Egypt, Czechoslovakia because that's where archeologists have had access to dig.
At a 13,000 year old cemetery in Sudan, over 40% of the skeletons had spear or arrow points embedded in them. The wounds--there were children buried there--the wounds found from the children in the cemetery were all execution shots in the head or the neck. They were just bashed to death in the head or the neck. This was not like one burial from one horrific incident, it was used over several generations. It was a continuing cemetery, and many of the adults showed not only the wounds that caused their death but many prior wounds, bone cracks and skull cracks that had healed, so you can see both a wound from some prior conflict which had healed and the new wound which caused the death at this moment. Individuals had gotten into a lot of conflict: one skeleton had 20 different wounds. That means bone cracks that you could still see 13,000 years later, and soft tissue injury we just don't have any way of knowing about.
When you get to modern times, still prehistoric, meaning before we have any written records--before anything you'd call civilization--things get a little stylized, that clearly culture is advancing. There's a middle Stone Age cave in Germany, only 5,000 to 10,000 years old, where there are two caches of skulls, just the skulls are there. They're neatly arranged like eggs in a basket, and they are the disembodied heads of men, women, and children with multiple heads--multiple holes not by axes into their skulls. I don't have--they didn't show a picture of that, but this is a modern version of it. This is actually from Thailand; this is the way skulls can get arranged. This--that picture has a totally different kind of purpose.
How many of you remember ice man? The guy that got unfrozen from the Alps; you're all aware of this. In 1991, one of the glaciers in the Alps disgorged this Stone Age man who had died they think 5,300 years ago. As at least a good number of you know, he had a lot of press and he was called the ice man. Since it took 5,300 years for him to come down the mountain, he must have died pretty high up in some high point of the pass in the mountain, so it was just assumed that he died--froze to death--while trying to cross the Alps and got encased in the ice and 5,000 years later came down. For ten years academic opinion said that, and then they finally got around to taking a CAT scan of the body. Guess what they found? A two centimeter flint arrowhead had ripped through his scapula and lodged six centimeters deep into his shoulder. He had been shot from behind by an arrow and he died of internal bleeding. Again, a violent death.
You come to even more recent times, a Native American settlement, American Indians from about 1325 A.D., so almost 200 years before they have any contact with westerners, and this contains the remains of 500 men, women, and children. This is not a great picture, but again, what you see that these victims had been scalped, mutilated, and then something a little unique, left exposed for a few months to scavengers before being buried, again, as a form of punishment, disrespect, or whatever. For the victim you not only slaughter them, mutilate them, maybe mutilate and then slaughter them, and then you leave the scavengers to chew on them and then finally they get buried.
In short, archeology documents warfare in every well-studied region for the past 10,000 years, which is when we have very good records. That's what you can dig up. The other thing is to look at currently primitive human beings and ask how many of them are truly peaceful. The anthropologists now take over from the archeologists. What the anthropologists find is that 90% to 95% of known societies have been involved in war that we can document. One sample of 50 societies, 45 engaged in war frequently; 4 did not engage in war because they had recently been driven into isolated refuges by warfare.
Have any of you been to the Aymara Indians in Lake Titicaca in Peru? It's a big tourist spot. There's an island in the middle of Lake Titicaca, and they're very peaceful people, they live on reeds, they don't have anybody to fight. They were pushed off the mainland by war and they've just been isolated, so that's one of the groups that's--well we haven't seen them get into any wars but they have no possibility of it. One which is called 'peaceful,' the Moonachie, which live actually in the Sierra Nevada Mountains of California they say--we'll call them peaceful because they only rarely go to war.
In another study 66% of primitive societies went to war every year, 75% at least every two years, and up to 90% went to war at least once every five years, so the evidence is mounting up that so called primitive humans are not a terribly peaceful lot. The Dani tribes of New Guinea had seven full battles and nine raids in one five and a half month period. Some anthropologists was sitting there for five and half months and that's the number that he counted. One Yanomamo Village, that's in Venezuela, was raided 25 times in 15 months. In the U.S. West, 86% of the Indian tribes went raiding or had to resist raids at least once a year.
Now you come to groups that are usually peaceful, so there's a group in Malaysia called the Semais and they were recruited so--but during World War II, as you know, the Japanese took Malaysia, and the British incited a sort of guerilla movement against the Japanese; so they were retained as scouts by the British to fight. I'm sorry this was later--this was--they've--they were scouts to fight the guerilla insurgency by supposed communists. Eventually some of the guerillas killed a few of the Semais, a few of their kinsmen, and then even though they had never been known to be warlike they become extremely warlike. One Semai veteran recalled, "We killed, killed, killed, the Malays would rob the corpses, but we did not want anything. We thought only of killing. Wah! Truly we were drunk with blood."
It sounds like their culture, like many cultures, have repressed the killing instinct, or killing propensity for one reason or another, and then when the cultural controls came off, boom, the instinct just roars up, totally full blown, almost instantaneously. We've seen that in so many cases. In Yugoslavia recently where people lived together for a very long time in moderate harmony, all of a sudden, bang, they start killing each other. The Germans in the 19--before the Depression in the 1920s--were among the most civilized people on earth in science, and education, boom, they become savages almost immediately. I think the indication is there's something inside of us ready to pop out. Culture can repress it, but demagogues know how to stick their finger into populations and pull out that us/them and vilify the "them" and bring us right back to chimpanzee days.
You all know Yale has a center for study of the Cambodian genocide, where now one group of people, the Cambodians, sort of split into two and the slaughter was terrible. How many of you have seen the movie The Killing Fields? How many of you know about the Cambodian genocide? Again, most of you, but not all of you; it's one of the most recent, most horrific kinds of killing.
This killing is--can be--what basically happens is that one group does not consider another group humans, and if you look in primitive languages, very often the word for human is the same as the word for their group whatever their group is. In the American Indians that was also a common kind of phenomenon.
There's a good report from March 18, 1690 in Salmon Falls, New Hampshire, where a girl named Mercy Short lived. They were raided by the Abenaki Indians; that was at that time 1690, a real frontier town. Mercy saw them kill her parents and three of her brothers and sisters. She was taken to--on a long winter march to Canada, and the captors sort of dragged her up to Canada. During that March she saw a five year old boy chopped to bits, a young girl scalped, and was forced to watch with her hands tied as another fellow captive was stripped, bound to a stake, and tortured with fire, after which the Abenaki "danced about him and at every turn, they did with their knives cut collops of his flesh, from his naked limbs, and throw them with his blood into his face. Remember this is someone who is already a captive with his hands tied so there's no immediate threat.
It's a clear sign of just not considering these out-group individuals as humans. All chimpanzees have one set of morals toward an in-group, and as I've told you, that in the wild the male/male conflicts never result in death nor do the male/female conflicts within a group, but in an out-group if possible they always result in death.
Now what does one think of this? There's a very interesting story from early America, it's actually Amerigo Vespucci, after whom America is named, and you know Columbus discovered America in 1492. Ten years later they were exploring all around and Vespucci went on a--one of the exploration expeditions along the coast of South America. He had some interactions with the local tribe's people and had some interpreters on board. Columbus had brought some natives back to Europe, and they were able to do some kind of translation. He was very interested in how different they were from Europeans.
"Their marriages are not with one woman but with as many as they like, and without much ceremony, meaning they just get married very causally and we have known someone who had ten women married to him. They are a very prolific people, [meaning having lots of children], but they have no heirs because they hold no property." Even childbirth is without pain, "Women in parturition do not use any ceremony as ours do. They eat everything, go on the same day to the fields and wash themselves; it seems that they hardly feel their parturition." Parturition--giving birth--now you can see that what he's dealing with in the 1500s, the late renaissance attitude, political science theory. What is it that causes wars between societies, which they had lots of back then.
One of the issues is original sin, these are very religious people, and what was the major punishment for Eve's eating of the apple? Pain in childbirth, severe pain in childbirth; here were some people that had no pain in childbirth, and he waxes poetic about that. Were they absolved of original sin? That's the kind of issue that's in his mind.
He also says, "They are people who lived many years, and according to their succession, we have known many men who have four generations living." So that's about 80 years--what is he referring to here? Again, from the Bible; the span of life, what's the span of life? 70 years, very hard to fit four generations into that, so again, he's reflecting that these are not people like European people. He goes on with all the wonders of their civilization, or their un-civilization whatever you want to call it.
But, he says, "They are a warlike people, and when they fight they do so very cruelly, and that side which is lord of the battlefield bury their own dead, but the enemy dead they cut up and eat. One of their men confessed to me that he had eaten the flesh of more than 200 bodies." Continuing, Vespucci talking, "The most astonishing thing about their wars and cruelty is that we could find no reason for them, since they have no property or lords, or kings, or desire for plunder, or lust to rule, which seems to me to be the causes of war and disorder." Again straight late renaissance theory and political science theory. "When we asked them to tell us the cause of the war and disorder they could give no other reason except that this war began among them a long time ago and they wish to avenge the death of their ancestors." It's a very interesting passage, the Indians--Vespucci's idea is that original sin is what causes this and then political--the sins that humans do have the lust for power, etc., is what causes all these wars and none of that fits these South American Indians.
The same message, that -- it's not obvious what the cause of these wars is, comes from modern anthropology, so the Yanomamo of Venezuela and Brazil who are very violent people, there was a book called The Fierce People that describes them. They're very, very warlike. They're in that border between Venezuela and Brazil; they're involved in almost constant warfare and yet what are they after? Yanomamo villages are surrounded by abundant unoccupied territory. They're just not settlement, to settlement, to settlement, there's plenty of space in which they could expand. Napoleon Chagnon, who you may have heard of, the anthropologist who studies the Yanomamo, believes that the fighting between them was apparently motivated only by desires to exact revenge and capture women.
We seem to have come across this before, but again, just as in chimpanzees, in primitive warfare females are killed as often as they are captured and most of these primitive tribes, as well as modern people's, have difficulty getting food, not as a cause of war but as a result of war. Things get so disrupted by war, that's the reason they have trouble getting food.
All of this is archeological and anthropological, studying times or peoples who don't have really any writing system. So in a sense it's prehistoric. Once we come to writing, the record of violence flows hot and heavy. The first account of the exploits of mortals is our military histories. The earliest writing of the Chinese, of the Greeks, of the Romans, are concerned with wars and warrior kings. Most Mayan hieroglyphic texts are devoted to the genealogies, biographies, and military exploits of the Mayan kings. The earliest Egyptian hieroglyphics record the victories of Egypt's first Pharaoh's. The first secular literature written in cuneiform recounts the adventures of the warrior king, Gilgamesh.
The early and extreme warlikeness of the earliest civilizations is laid out in the Bible. You just read the Bible and you get the whole message I'm giving you. The earliest written part of the Old Testament, Exodus, recounts the brutal Hebrew conquest of Canaan. Numbers 31:7-18, The Israelites get the Ten Commandments. Thou shalt not kill. And then they go off to conquer Canaan with lots and lots of killing. They waged war against the Midianites as the Lord--this is one of my favorite passages: "They waged war against the Midianites as the Lord had commanded Moses and killed every male among them, but the Israelites kept the women of the Midianites with their children as captives."
When Moses learned about this, the captains came back, thumped their chests, we've had a great victory; we've killed all the men and here we have the women and children as captives, Moses becomes angry: "So you've spared all the women, why they are the very ones who prompted the unfaithfulness of the Israelites toward the Lord. Slay therefore every male child and every woman who has had intercourse with a man, but you may spare and keep for yourselves all girls who have had no intercourse with a man." An echo of the chimpanzees who, when a female tries to transfer if she has children she's a goner, if she's young, presumably a virgin, then she will probably be allowed to transfer.
After the fall of Jericho the Israelites, quote, "Put to the sword all living creatures of the city, men, women, young and old, as well as oxen, sheep and asses." Next they attacked Ai, "there fell that day a total of 12,000 men and women, the entire population of Ai." The clear thing, it's quite striking how this comes so soon after the Ten Commandments, that what's clearly going on is, just as chimps--is an in-group, and clearly the Ten Commandments is -- intended for the in-group, 'thou shalt not kill,' straight chimpanzee. However, out-groups, if you don't kill them all you're not obeying God's commandments.
In very modern times atrocities continue with no lessening of the horrific nature of it compared to chimps or early human beings, and I'll describe one famous event to you which--how many of you know about the rape of Nanking? Again, not all of you, all of you should know these things that I refer to are very important things.
This is during World War II in I think it was 1937. The Japanese were trying to conquer China, and it was a big place and they were getting rather frustrated because--in Japan it's a small place, in China it's a huge place, and it's not an easy thing to do. But they captured a city called Nanking, south of the Yangtze River. In short order, the Japanese slaughtered 350,000 people. The total population of Nanking at the time was only about 650,000 and several hundred thousand had already fled. In short, they basically killed every Chinese that they could find, just like the Bible stories, or the chimpanzee stories.
A Japanese newspaper reporter watched Chinese prisoners being bayoneted on the top of the city wall. "One by one, prisoners fell down into the outside of the wall, blood splattered everywhere, the chilling atmosphere made one's hair stand on end and limbs tremble with fear." This reporter is talking only from Japanese and we'll see, Nazi sources because it's possible the Chinese sources may be exaggerated or something, but the belief is that neither the Japanese nor the Nazi sources would exaggerate.
Another Japanese military correspondent, even more constrained, described another locale where the murders were by samurai-style decapitations. "Those in the second row were forced to dump the severed bodies into the river before they themselves were beheaded. The killing went on nonstop from morning until night, but they were only able to kill 2,000 persons that way. The next day, tired of killing in this fashion, they set up machine guns. So great was the slaughter that the Japanese general complained that he could not find ditches deep enough to bury the enormous pile of corpses."
Tens of thousands of Chinese women were raped, often in schools and nunneries, thousands more were put into sexual slavery, forced into prostitution, and referred to in Japanese as public toilets, the women forced into prostitutions. Many soldiers went beyond rape to disembowel women, slice off their breasts, nail them alive to walls. Fathers were forced to rape their daughters and sons their mothers; not only did live burials, castration, and the carving of organs and roasting of people become routine, but more diabolical tortures were practiced like hanging people from their tongues on iron hooks, or burying people to their waists and watch them being torn apart by German Shepherds.
So sickening was the spectacle that even the Nazi's in the city were horrified. When the Japanese took Singapore, right after Pearl Harbor, they shot and decapitated another 20,000 Chinese. That was just a modern example to show you that whatever this is in humans that makes us want to kill members of another group, it is totally unfettered by anything that you might call control or civilization, when it breaks out the violence is just incredible.
The bottom line is that war seems to be characteristic of almost all, and possibly all human societies at all times in our history. There is no example, no period which we can find out, where there's a discontinuity between the chimpanzee behavior and our current behavior, and so again, I think whatever you think of what's causing the chimpanzee war, you probably have to consider very much the same explanation for human war.
The amount of death--I showed you one example from one tribe, the Ache in South America, and any one tribe's experience may or may not be characteristic. This is from a book, Lawrence Keeley, War Before Civilization, which traces a lot of the information I've been giving you, and what he does is, he collects all the data that anybody's ever collected, so that he sort of can get some idea of the percentages of deaths by war. This is percent of deaths from warfare--this is males, and this is everybody together, and these are different tribes at different tribes for whom we have data.
You'll see that the numbers--the male numbers go up to 50% or 60% of male deaths are from these wars, and the deaths of everybody which is this, is somewhat smaller, a fifth or a sixth, 15% to 20% of deaths, but going up of course to 40% of deaths. The point he's trying to make with this graph is, here's primitive warfare, these darkly colored bands, what he calls primitive warfare, and the white bands are so called civilizations and he calls civilizations anything that has a state, like the Aztecs had a state in one of these it is Aztecs.
From the data that one has we are--even though we think of World War II and all of these current and incredible wars and all our technology devoted to war--what's happening is that we have much--many, many more people die then did in the past but the population of humans has grown so much that the percentage is not so huge, and that wars are less frequent. Rather than having raids almost continuously as in a lot of primitive warfare, we have wars every 15 or 20 years or so in general between any two groups fighting each other.
What he shows, again, from the data that has large and unknown error bars--the civilized warfare which is the Aztecs, France in the nineteenth century with Napoleonic War, the 1870 War, Western Europe in the seventeenth century lots and lots of wars in the 1600s, U.S. and Europe in the twentieth century, World War I and World War II and so forth, that as far as he can tell the fraction of all deaths that is caused by war is decreasing.
One possible very nice way of looking at human history is that humans have some sort of a propensity, call it an instinct if you like, to identify an in-group and everyone else is out-groups. These in groups can be nationality, they can be religion, they can be color of skin, they can be language. Language is a big source of conflict in Canada and Belgium, all kinds of places; almost anything will do. It can be Yale versus Harvard, or Berkeley College versus Calhoun College, and Red Sox, the Red Sox fans. The English who are generally very civilized, get into a soccer stadium and they start killing each other.
Humans have this enormous desire to identify in-group and out-group. We even now pay to advertise a company, because anything that looks like a group membership symbol, humans love that, and will pay a lot to have a hat or a name of some team, or even some company on them. We have very different morals towards the in-group and the out-group. It seems that that's what's still going on in us, that as time--we have that still. But as time goes on, because of increased communication and increased education, probably what we consider the in-group grows.
First it was your little village, a little hamlet of 40 people, and then maybe organized into some sort of a tribe of 1,000 people and gradually it grows. If you read the history of Europe there are all these little cities, say Greece with city-states, a whole city could be considered one family, with a lot of divisions within it. Renaissance Italy you have the Medici's and the Pazzi killing each other, families within cities, but gradually it grows. You get nation states, and as they grow, the wars get less because people within say France don't generally have wars with each other, but France will have a huge war with Germany.
The group that people consider "us" gets larger, the frequency of war goes down, but since you have so many people fighting so many people, the war causes more and more deaths. Possibly, this is optimistic, that as we become more interconnected and we consider more people "us," and fewer people "them," that gradually this behavior will disappear. But that's just guess work.
Now Keeley, who gathered a lot of this data, he has his own summary. Again, in frustration about not really understanding … what these wars are all about, he does not accept any idea that there's any biology involved. He says, since he can occasionally find some group that hasn't been to war for 20 years or something like that, then it can't be biology. The view of biology that many social sciences have is sort of that --….--if it's biology, it's a knee jerk reflex. If you're not--if your nervous system is not impaired, every time I hit your knee with a hammer your knee will kick out and there's no volition. They say if we ever see a human not doing some behavior, that behavior cannot be instinctual.
Of course that was disproven in around 1910 by Pavlov, you all know about Pavlov? He takes an instinct as basic as eating, and a dog sees a piece of meat and starts salivating, and then very rapidly he rings a bell a minute before the dog sees the meat and the dog starts salivating to the bell. Since 1910 at least we've known that even the most basic behavior can be controlled by something with as small a brain as a dog, even though one would never say the dog does not have an eating instinct, does not have a salivating instinct, of course they do and yet dogs can control it.
I tell a story about my dog, so a smallish white Samoyed, and I'm at work all day. I work long hours and so she's at home all day and by the time I come home she's a little frustrated. She's been cooped up, and I'm a little frustrated. So what happens: I get down on my hands and knees and I growl at her. She immediately picks up the cue, she's snarling back at me, and then I swat her one, a gentle swat but she gets--she snips back at my hand and we go at it. We have a great time. Unfortunately my dog has died, but we had a great time and in the course of these she's snapping--she's aroused, her hair is standing on end, her tail is straight up, her fangs are showed, and she's snapping away at me and I get, maybe--we do 20 minutes or so maybe--at least 50 to 100 bites where she actually wins. I win, I smack her, she wins and--so what that means over the years I've had many tens of thousands of times where she's grabbed me and all that, and guess what, not once in all those many thousands of bites has she ever pierced my skin.
All right, this is a peaceful house dog; she doesn't know anything about killing. No, not true. In the morning I take her out running in the woods, I don't know if she takes me or I take her, and if she sees a bird or a squirrel, she's off and she comes back with a dead bird in her mouth, clearly killed, she clearly bit through their skin--very, very proud, walking there with a dead squirrel. Here's an animal and I love her dearly, but her brain is not very big, and she can get into the depths of real instinctual responses and yet her brain is clever enough to be able to control it and not--and to kill the squirrel but not to kill me or not even break through my skin.
I think the idea is a lot of people think when you've described biological basis for behavior that it's inevitable. The human species were lost, we're never going to change, but that's nonsense. Humans are like chimpanzees, we're quite intelligent, and we are capable--we have instinct, I believe that we have instincts for sure, you'll see it come out in the most horrible ways and in some good ways, but it's not that difficult to control. My dog can do it, you guys can do it.
The other issue which--these are good topics for discussion in the sections--is, some people also say when I describe duck rape or orangutan rape, that some of--my describing it and saying that animals do it I'm justifying it. There's this whole thing now that what's natural is good and what animals do is natural and therefore it's good, and it slops over to foods and everything. This whole idea of natural law, that you can tell from nature what is good and what is bad is not to be taken seriously. That finishes that topic, and I think you've had enough violence.
I want to skip--switch to the opposite side now. Demography is, of course, births and deaths; those are the two main things in demography. We have been talking about one of the main causes of human death on one side, and we find that there is a clear continuity between chimpanzees and humans. Now let's talk about the other side, births and there surprisingly, humans are drastically different from chimpanzees.
How do we know this? Chimpanzees were never very successful demographically. At their peak there may have been two million chimpanzees. A very small Chinese city is two million individuals, and now because of the rise of humans they're taking over their territory, the guess is they've been reduced to about 100,000; 5% of their peak population. They are restricted to central Africa; they have never spread beyond central Africa.
Humans, on the other hand as you know, number in the billions; we've spread to the farthest corners of the earth from the ice cap around the North Pole to the hottest desert and jungle. There are tens of thousands of times as many people, humans, as there are chimpanzees, and humans have become absolutely dominant basically everywhere on earth. From a demographic point of view, maybe the first question we should ask, why are there so many humans and so few chimps? What is the secret of our demographic success?
Let me give you a clue about the time scale. We separated from chimps about six million years ago, and I've shown you--this is another version of the deaths--don't worry about it. Remember this--the family tree here, and here is the split point where humans branched off from chimps and bonobos and its ballpark six million years ago that we split off. The population size, what is believed, that the population size of all--the group that became these three species was only about 50,000 individuals at this split point. That comes from the genetics, the variation in genetics.
This small group branched off and started behaving--evolving quite differently. What happens when you have a small group to begin with of 50,000 breeding individuals, then a small group breaks off and they may further subdivide into smaller groups that may not come much in contact with each other, you have inbreeding, and inbreeding causes a lot of genetic problems, but it also allows evolution to go very rapidly. For mutation, if it is beneficial it appears, it can spread to a small population very rapidly whereas it's extremely difficult for it to spread into a large population. The tinyness of the number of our human ancestors allowed a rather rapid evolution away from the other groups who were also evolving of course because they were also in small groups.
That--at the split you start going down this pathway and it's shown here as a single line, but as all of you know from the newspaper, there are many, many species splitting off at different times with different characteristics all in the humanoid, hominid line and by chance all of those other species went extinct except one. That's another characteristic: if you're a small group then it's very easy to go extinct. And all of the--we know 20, 30 other humanoid species, and all went extinct except one. The genus Homo, which is the group of species in which we sit, originates about two and a half million years ago, and they start calling skeletons Homo sapiens about a half a million years ago, but even though they're Homo sapiens their brains are, at that time, significantly smaller than ours are now, and anatomically modern humans date only from about 100,000 to 150,000 years ago.
All during this period the number of humans was clearly very small. It's very humbling to realize that with a small group that's evolving rapidly, which means it's not yet mastered it's environment because you don't--once you have optimized your relationship to your environment evolution slows down, but if we're evolving rapidly that means we haven't yet mastered it. So a small group struggling in its environment, very likely to go extinct; most of our sibling species went extinct, and I think with a very small role of the dice differently the line towards humans could easily have gone extinct.
It seems that about 100,000 years ago there was a bottleneck in the growth of human species, and the humans living at that time, a small group, were the ancestors to all current human beings. There was a small population of about 2,000 to 10,000 they believe, and that the total human population, from 2,000 to 10,000 of humans living in Africa and interbreeding. There may have been other human populations somewhere else that disappeared. We don't know, and the numbers 2,000 to 10,000 some research puts them a few times higher, we don't really know, but again a very small number.
We know from that period that there was no substantial population growth, so that means the average number of surviving children was two or maybe teensy weensy bit higher then two, so that meant when you have on average two children per couple, that means that most lineages have died out, that most individuals who were living at that time of this small number now leave no descendants at all.
If you trace back, the genetics suggest that all current humans, all races all over the world are the descendants of a single human female. That every other line, from the time when she was alive has died out, and similarly for males, we are all the descendants of a single human male. All other lines have died out, and those two didn't have to live at the same time. In fact, almost certainly did not live at the same time; it's just the randomness of lines dying out and the genetics tells us that we know the rate at which DNA mutates and diverges and so we--and we know the range of a variation in current humans so we just sort of narrowed that back and it goes back to this--what did I say 100,000 years ago.
That's the genetic Eve and the genetic Adam that the newspapers just love this story but it's just a common result of -- a population that doesn't have a lot of surviving children--lines are going to die out. You can read that the royal houses of Europe is where you're all exposed to it. Look how few generations the royal houses last before they don't have any heirs, and that's in modern--these are the richest people at their time and have all the food and protection and everything that they want and they can't stay going for more than a few generations.
In primitive times, the rate of extinction of lines was great. About 50,000 years ago--we're going to spend a few million years in Africa, then about 50,000 years ago a group of humans migrated out of Africa. Again, the numbers and the times, some people say it was as late as 25,000 years ago that they migrated out. Then amazing things happened, once they burst out on the rest of the world, they spread everywhere. Humans are found everywhere on the Eurasian continent, that's from Siberia to Spain by about 20,000 years ago, and then from Siberia they crossing the Bering Strait, which was a land bridge at that time, and expanded into the Americas and reached the very tip of South America by 10,000 years ago.
In 40,000 years which is a blink of an eye in evolutionary terms, humans spread everywhere on earth, an incredible population explosion. This is the first and greatest explosion, a population explosion of humans. You should note that something was making us superior at that time, and clearly it has nothing to do with modern technology. All of this fantastic expansion even pre-dates the invention of agriculture and most of what we consider civilization starts with agriculture.
What is the main difference that has allowed this story that humans have done this and chimps have done this? Well you ask, what is the reproductive rate of chimpanzees? Well I've told you that a chimp mother has one young every five to eight years, so at that rate it's going to be very hard to increase at any great speed. Human females have babies much more frequently, it's quite possible to have a baby every year, or every year and a half, or two years, and this is common--my brother was born 20 months apart from me. How many of you have siblings less than two years apart? Most of you.
So humans are quite capable of doing something that chimps just cannot do. They have a rate of reproduction of about four or five times slower than we do. The mothers, the chimp mothers cannot take care of more than one young at a time. They will have a young that's clinging to them and then perhaps an adolescent son or daughter with them but they'll never--you never see two infants at a time, whereas, humans can easily take care of two infants at a time.
Twins in chimps? I have never heard--read anything about chimps occurring in--twins occurring in chimps, and I don't know whether they ever do. It may be just that we don't have enough observation that maybe occasionally chimp twins do happen, but it's not been reported that I've seen. Anybody take a--
Student: Not about twins, I was just going to ask if that's regulated by hormones completely. Like you would say that lactation stops--
Professor Robert Wyman: Yes.
Student: But it's a chimp is nursing a baby for five years?
Professor Robert Wyman: They're nursing them for a long time. I don't recall what the number is, but there's many behavioral mechanisms. So in nursing, the actual physical stimulation of the nipple releases hormones, Oxytocin, [more likely prolactin] which prevents ovulation again, and that can be prolonged for quite a period of time but is not absolute, so there are other behavioral mechanisms, other internal hormonal mechanisms which ensure this and in chimpanzees we--it's very hard to capture a chimp and do the physiology and experiment, so we basically probably don't know most of the answer to that question.
The--a major difference -- between humans and chimps is a tremendous increase in human fecundity. Now in demography we use the word--fecundity means the ability to have children. Fertility means the number of children you actually have, and that comes from French usage and French use the word sort of oppositely to the way we do and demography was born in France. When I say fertility I don't mean the ability to have children, that's fecundity, but I mean the number of children that any given set of women actually have.
We have to ask ourselves what evolutionary factors allowed this change in fecundity. What limited chimp population, what limited chimp fecundity? Well in primate evolution the main factor is the time that brain development takes. A body that's capable of walking and chewing and so forth can develop rather rapidly in all kinds of animals, develop in a very short time scale and are immediately capable of doing those things, but if you're going to have a species with a big brain, that's a slow process. In all the higher brain--the bigger brain primates, the slow thing is brain development.
In order to not have to carry this baby like for--until the brain is mature at age 13 or something--they say we don't really progress beyond adolescents--so in humans and great apes the baby is born with physically somewhat mature but the brain is still growing enormously. Really there's post-natal development of the brain, so even at the nine months of pregnancy, we're not at the end of the period of brain development. The brain is nowhere near its final size or complexity. That limits the rate at which one can have childbirth and because the infant is born in chimps and in humans, is born incapable of taking care of itself, the mother has to stay with the child and take care of it.
In chimps the mother stays exclusively with her infant for several years. The chimps get very little, as I mentioned, very little in the way of resources from the males. They mostly watch and they do--they don't come in contact with males all that much, they and their young forage by themselves, and etc., etc., and the males are just patrolling. They see them every so often and the males protect the boundaries. In terms of taking care of the young the males basically have no role whatsoever. As a result of this need to have intense care of the young, and no help from anyone, sometimes other females will help, but basically no help at all, the period in which the mother has to devote herself exclusively to that one young is quite prolonged.
Now in humans, males do play some more intimate part in child rearing. Not anywhere near as much as a female but they do bring resources. In general, in most human societies over time, males are responsible for bringing some resources to the female on a rather continuing basis. We don't really know how this evolved because these things you can't really tell these things from fossils.
What we know is that Africa--the chimps started in the jungle and then Africa started drying out and so some subset of the chimps, maybe pushed out by stronger individuals or clever individuals, were pushed into this drying out grasslands where there was less cover and less fruiting trees. Dry land doesn't produce the big fruiting trees that chimps depend on. As a difference between chimps and bonobos, when there's a lesser food density the population has to spread out. That if an individual is going to find any food they're not going to find enough for a large group, so individual females would have to go forage quite separately.
You can speculate further that as the females spread out, the dominant males could no longer keep watch over and control over these females, they were just too far spread geographically. While in chimps--while the male or female may go off for a short time period, in what's called a consortship and there may be matings at that time, there's no lasting, no continuing relationship between any particular male and a female. Chimpanzees, as I mentioned, are male bonded and they spend more time with each other, male to male, than the males do with the females.
In humans of course we still have a lot of what they call male/male bonding, military units, sport teams, all male clubs, football, pre-wedding parties, watching football, watching parties, etc., but we've evolved in the direction of much more male/female interaction and contact. Female sexuality changed. While chimpanzees always mate from behind, humans engage in frontal copulation, and since the face is how humans and also chimpanzees detect each other--they know individuals largely by their facial structure--and they detect emotions, it's a very important part of communication to detect the emotions and respond to each other by facial cues--so this face to face interaction, especially in the intensity of the sexual encounter is considered a large part of the evolution of male/female bonding.
I forgot to show you last time, but it's an excuse to show you this time, here is a bonobo engaging in front to front sex, male and female here, and she's grinning. She's clearly being pretty happy about this, and I also said I would show you--this is two females doing the same thing. If you didn't--if I didn't tell you it was--this was two females you wouldn't know the difference. Unless you're watching you can see that they both have their swellings, that's how you tell that they are two females. I mean the guys who took the picture obviously knew a lot more but you can tell that--so this is what I described--that the locals call hoka, hoka. This whole evolution of sexuality in the human line, the clitoris has moved forward for--which in face-to-face copulation probably makes it--more female pleasure during the act of copulation and therefore again reinforces this bonding.
Another big difference and this is not an extreme case of the rump--that's another topic. Humans do not advertise their estrus. Not only do we not--remember the chimps advertise their estrus in order to get the males together and have the males compete for them. Humans keep it secret; not only don't the males know when a female is in estrus, but the female herself does not when she is estrus, and for a very long time it was believed that females are fertile during their periods. It was only in the 1930s that it was found out by a Japanese group that females are fertile in the mid-period between their periods, and even further, it was believed in the 1930s that females are fertile a few days before and a few days after the middle of ovulation in the middle of the period, and in fact, we now know just from about ten years ago that the actual fertile period always is only precedes ovulation. Then intercourse must take place before ovulation.
Not only do we--do human females not advertise to the females, they don't know, and scientists, with all our investigations, have just now finally figured out, we think, when a human female is fertile. This is a big, big change. It's such a big part; the advertising is such a big part of primate sexuality, why has it disappeared in humans? It may be sort of the reverse, that if females are out there alone and there's carnivores, you read about this from the Ache, that there are lions and tigers out there ready to eat them, and they need protection of various sorts and maybe help in finding food, so it's important to have a male hanging around.
A male's evolutionary purpose is he wants to inseminate the female, so if he knows when a female's having estrus, he has to be there then to inseminate her. If he knows when she is in estrus he also knows when she is not in estrus, and when she's not in estrus he may have no evolutionary push to stay there but go out and try to find some other female. The purpose of not showing your estrus may be to keep the male uncertain of when you are fertile and therefore he has to attend to the female all the time, and once he's there he might as well help her because that will insure that whatever infants come along are in good shape.
If that's correct, and certainly males and females started spending more time together, and they're more dispersed; that reduces male/male competition. Remember the male/male competition is a result of a group in which a lot of males stay together. When you're more dispersed, male/male competition has to be reduced. It looks like in the evolution to humans that's--what's switching is from the advertising which allows the males to compete and the female gets the male with best genes, she's switching to wanting resources from the male. She's no longer interested so much in male competition but in whatever resources the male can bring to her by having a male around continually.
This story is rather complicated and very controversial and there's a very nice reading in your packet. It might be interesting to consider that, how does the male respond to this change in strategy? If the road to monogamy starts going down then paternity becomes more certain. In the chimps, where the female is copulating with everyone, there's no reason to be certain of paternity at all. Once it becomes clear that, yes, this child is almost certainly mine, then it becomes evolutionary advantageous for the male to start putting resources into this mother and child because that insures their survival and things start developing in a different direction. Where stable pairing becomes an evolutionarily advantage, the male putting resources into the pair are for evolutionary advantage.
It seems pretty clear that an increase in the male contribution to child rearing is one of the major reasons for the increased fertility of humans--why humans are able to out reproduce chimpanzees. Of course, as you all are aware, monogamy has not by any means taken human societies totally over and some societies overtly sanction polygamy, but even in our culture which Europe and North America--genetic testing shows that 10% to 15% of humans do not have the father that they're supposed to have. 'Father' is usually defined as the resident male; he's not the father, and that's quite a large percentage.
American women report 6 different sexual partners lifetime and males report 16 female partners, lifetime. Now one thing we know if you're at all mathematical that the--since it takes two to tango, the average has to be the same so it can't be both 6 and 16, and who knows possibly somewhere in between is correct, but probably higher because these things tend to be under reported, no one wants to really say--well females certainly don't want to say how promiscuous they are usually and also that's old data. This is from 2001 and with the change of sexual mores in the Western countries, I'm sure the numbers are exponentially increasing.
What's--another thing about this thing with respect to human evolution is that when you're a chimpanzee the male--the main form of competition is male/male fighting, male/male status jockeying which takes a certain amount of intelligence to arrange coalitions and so forth, but basically evolution is pushing you to be big and violent. Now the individuals disperse, the male stays with the female, the males starts bringing resources, violence is decreased. The importance of that in the male evolution decreases and the importance of being able to provide resources become evolutionarily important, so the kind of intelligence required to find food in a scarce environment, to find shelter, to protect from animals and so forth becomes important.
A fair reason for the increase in human mental capacity might also be this shift from a dependence on violence for competition to a dependence on acquisition of resources for competition and for evolution. I've run out time and so we will continue with humans and how they are different from chimps next time.
[end of transcript]