When Humans Were Scarce 
When Humans Were Scarce
by Yale / Robert Wyman
Video Lecture 4 of 24
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Date Added: November 8, 2009

Lecture Description


Hunter-gatherer populations were much less dense than later agriculturalists. The variety of their food supply protected them from crop failures and their sparseness reduced the spread of infectious diseases. Hunter-gatherers were healthier and worked less than early agriculturalists. Why didn't their numbers increase up to the same level of Malthusian misery? Their numbers may have been limited by violence between groups. Agriculture is more work intense and offers a less varied diet. Populations seem to grow rapidly and then die out suddenly. Populations are subject to climatic- or disease-caused crop failure. But farming allows individuals to produce a surplus of food that can then be stolen by warrior tribes or military castes. The surplus allows for population growth, cities and stratified societies. The death rate, until perhaps the 1700s in Europe, is enormously high: only approximately a third of women survive to the end of their reproductive period. At this death rate, surviving women who are able to reproduce must have more than six children on average or the society goes extinct. All the great religions and cultures develop in this long period and all stress the requirement for high reproductive rates: "Be fruitful and multiply."



Reading assignment:

Hurtado, A. Magdalena and Kim Hill. Ache Life History: The Ecology and Demography of a Foraging People, pp. 1-6



Livi-Bacci, Massimo. A Concise History of World Population: An Introduction to Population Processes, pp. 31-36 and 42-48



Caldwell, Pat, John Caldwell and I.O. Orubuloye. "The Destabilization of the Traditional Yoruba Sexual System." Population and Development Review, 17, pp. 231-238



Geertz, Clifford. "Book Review: A Society without Fathers or Husbands. The Na of China." The New York Review of Books, Vol. 48, no. 16, 18 October 2001



Smith, Robert J. and Ella Wiswell. The Women of Suya Mura, chapters 4 and 5




Transcript



January 22, 2009



Professor Robert Wyman: As you may have noticed, the course has been proceeding somewhat historically. First with pre-primate animals, the whole evolution of sex from things that swam in the ocean, and then we discussed the primate mating system as you've seen--in the same sense as on the board. The first--the pre-primate is a few millions of years--I'm sorry, tens of millions of years; primates maybe ten million years or so. Then last time we started discussing the transition from ape to human, and evolutionarily modern humans date to something like 150 thousand years ago.



We're coming up to time and today we're going to discuss fully anatomically modern humans. They have the same brain capacity that we do, etcetera, etcetera. The earliest groups that we have any kind of decent demographic data on are hunter gatherers which would include cavemen and people that are hunter gatherers but do not live in caves.



Last time we asked why there were so few chimps and so many humans and today we're going to ask very similar questions about--we're going to start with, we're going to cover a lot more; we're going to ask very similar questions about hunter gatherers. There never was a great density of hunter gatherers. There is certainly not now and the question is, why?



If you look where hunter gatherers live now they--each small group, and the again the small group is the same size we've been talking about something like 40, are spread out over a very large area and they use that area to hunt in and to collect fruits and nuts, and whatever they can get from the trees. It looks like a very simple question, why is the density of hunter gatherers so low? Why are there so few of them?



For a long time, the answer was: they didn't have much food. That they needed all this space to get enough food to survive, and if they overpopulated that space they couldn't survive. In sort of modern hubris, we looked back and thought hunter gatherer is a very inefficient form of food gathering, not modern, and we're so much better than them now.



The data is quite clear on some part of those assumptions; hunter gatherers, at the time when all human beings were in the stage of hunter gatherers, before--farming starts about 10,000 years ago. There's--what is the number here? There may have been like two million people on the whole earth. Remember I said hunter gatherers spread out of Africa, spread amazingly over the whole earth, and maybe the total population of humans at that time was something like two million people. Now we have over six billion people, that's an increase of 3,000 times in the human population, so clearly there were fewer hunter gatherers than now.



This is a very--you'll see this in lots of discussions of this field, but it's a very elementary kind of consideration. It talks about the long scale of human demography, of human population growth, and we came out of being other species of primate, of hominids and we gradually grew up to some sort of a limit. There's the idea that the various productive systems that we use, like hunter gathering--limit is some sort of a carrying capacity limit, and so the idea is that the human population increased until it reached a limit and then for a very long period of time it can't get beyond that limit.



Then 10,000 years ago, maybe it's 12,000, farming is invented and all of a sudden the whole system changes, there's many more people and we jump up and then again reach a limit, and we'll talk about that as some Malthusian limit in this particular period, later we'll discuss that, and then around here the industrial revolution happens and all of a sudden the population increases again.



This is a logarithmic scale so it's not linear. Each of these jumps is by a factor of several thousand. That's a very, very schematized version of human demographic history and we're talking about this period. What limited hunter gatherers to this level whereas farmers could go up to this level. Again, the obvious answer and looking at this kind of rough data is that it was food.



Whoever then--archeologists, paleontologists go and actually try to examine this and there turns out to be the data does not fit that theory terribly well. What do archeologists do? They dig up skeletons and they have a good representative set of skeletons from the last 7,000 years in North and South America. One study looked at more than 12,500 skeletons so we're talking about a good scientific sample. What did they find out? These were set into communities, and communities lasted so much time, so you can date the whole archeological site to a certain period.



The medical anthropologists got into it and started looking at the bones and dentition and all this, and not only did they find the violence we talked about last time, but these people were also sick. They had diseases at different times. You could see bone problems and how well the bones grew and from the teeth how much calcium they had, and all this. What does it turn out, that contrary to the idea of progress that you'd think the later people were more healthy, in fact, it was earlier people in the--the earlier individuals that were healthier. As time goes on, the skeletons get less and less healthy, that they're getting less food and less good food, and were more subject to diseases.



It was quite a shocker when this status started coming out. The researchers attributed this decline in health in large part to the rise in agriculture. Two main factors they say, the rise of agriculture and the rise of urban living, and we'll talk about the urban story in a moment. If you again go like we did last time from the archeology to the anthropology and look at current hunter gatherers, it's a little bit of a distorted study because nowadays almost all hunter gatherers have been pushed out of the good lands that they used to live in, into very marginal lands.



You know this from U.S. History in high school, how the European farmers pushed the very earlier farmers or hunter gatherers of the American Indians, the Native Americans into Arizona, into desert, into the Badlands in the West, the dry Badlands and to the West of the U.S., farming peoples push hunter gatherers into inhospitable land.



There's a story in the Smithsonian Magazine recently about Pygmies in Africa. I don't know if you know a little bit about the history of African demography, which we'll also cover, but the Bantus have expanded from south--the bulge of southwest Africa basically all around and have pushed other people's out and the Pygmies are one of the groups that have been very severely discriminated against and really pushed into inhospitable places.



Another example is the Bushmen of Africa who were pushed into the Kalahari Desert in southern Africa. Even in the desert these guys eat 85 different species of plants, and it's almost inconceivable in their culture, for someone to die of starvation because plants will bloom some years and not bloom some years. They will get a fungus some year, or a virus, plants--any one species is not generally very reliable. When you have 85 different species to survive on you're not going to go without food. There will always be some group of plants that are going to be available to you and so you're not going to starve.



Further, the anthropologists lived with these people and they start writing down what they're doing at every point in time. Per hour invested, the Bushmen get more food then the early agriculturalists. Not modern agriculturalists who can drive a tractor and in an hour do a lot, but we're comparing hunter-gatherers to the first stages of agriculture. The Kalahari--the Bushmen in Kalahari spent 12 to 19 hours a week collecting food and the rest of the time they used for a lot more sleep than current farmers, and a lot more leisure than farming people, so life is more generous to them.



You have to think now, this is for people pushed into a desert, a very inhospitable place, and now if they--if you can imagine them living in a lush forest region where they originated, life must have been much, much easier so the amount of time exerted to get your basics of food and everything must have been much--a lot less. Not only do they have to work less and they get more food per hour, but the variety of foods is very good for you because you need different minerals, you need different other micronutrients, you need different vitamins, and as we are bombarded with in the popular press, a variety of foods is very good for you. You don't want to eat just one kind of food, so they had a very diverse and healthy kind of diet.



Agriculture comes in and indeed it enormously increases the amount of food per acre when land is limited, when you have a population density such that land becomes limiting rather than your time or your need, when land becomes limiting then agriculture becomes important because per acre you can get a lot more food than hunter gathering, but you have to spend lots and lots of hours to get that land to give you that amount of food.



The question remains 'why are there are--why were there and still are of course, why are there are so few hunter gatherers? Again, a Malthusian type question that, if we know they lived quite well, we know that later people going into agriculture lived a lot less well in terms of basics of life, how come the hunter gatherer population did not increase up to the same level of misery as early farmers, which is basically one of the earliest examples of a Malthusian type question. Malthus thought those same kind of thoughts but for a much later population.



Well in truth, we don't really know the answer to this and it's greatly argued about, but I can tell you some things that are known. Current hunter gatherers have a moderate number of children and many survive. They do not have an enormous infant mortality, certainly not compared to later populations which I'll show you that have a huge infant mortality.



If they are Nomadic, and I'll tell you about an example of that later, they have to move quite a lot and that means carrying children around. I think Bonnie has sort of indicated to you, even dealing with a lot of children in one place is difficult, but the difficulty of moving with very young children, and packing up everything and moving for a very long time, over a long distance is difficult and Nomadic peoples very often show very clear signs of some form of conscious population control. They know they can't cope with more than "x" number of children. We'll get to that all societies have indeed controlled their population but mechanism they were not totally--not clear what they think the reason for their doing things were, but Nomads apparently know what they're doing.



Hunter gatherers are moderately healthy. Again, their burden of sickness is not severe, again compared to later populations; however parasites are always a problem. I'll show you again a modern case of parasites. This is a girl, modern girl, current girl in Central America, and you may notice the swollen belly. You know what's inside there to swell it? Worms--exactly and when they purge her that was what was inside that girl, all those worms. Humans have had this problem since time in memorial. Hunter gatherers are not immune to this.



Infectious diseases they have less because they're in small groups, so infectious diseases as you know need large groups to keep spreading and they're hostile to their neighbors, just again like chimpanzees so they don't come in a lot of contact with neighbors, so diseases don't spread from group to group and each individual group is not large enough to allow for the maintenance of a disease.



Each village, if you--anthropologists go and sit in one village for a long time and they have a high population growth rate. Each village seems to be expanding quite noticeably, and you think, well in each village that we go study population is increasing, again, it doesn't make sense why haven't they--been living that way a hundred thousand years, why haven't they filled up their space? Why is each village surrounded by lots of--basically unused space?



Even today, a lot of the very tropical lands are not high--densely populated. We may have the image that they are but they're not. New Guinea is not densely populated. If you call densely populated--the Netherlands is I think the most densely populated in the world, Bangladesh, the livable regions of China, the livable regions of Japan, these are densely populated. The tropical regions of the world, nothing like that; New Guinea I said, Borneo very sparsely populated, the Amazon, Sub-Saharan Africa vast open areas, so these are not situations of high population density, yet any village that you sit in is increasing its population. What's going on?



What are the--what the archeologists find out is that when they study a site, and I sort of mentioned this already, what you see is this. You go to--you start digging a site and you actually dig in reserve, but you go to the bottom and you see there was nobody there before certain years, and then a small population, and what you see, you can count the amount of food remains, all kinds of things, the population grows more or less exponentially. That means that the same percentage every year. A half of a percent a year or whatever it is, and it grows up faster and faster, because there are more people producing that same percent of population growth.



You get this phase and then all of a sudden you reach the top of your pile and your village is gone and there's nothing there. Some sort of a crash happened, where if it's not totally gone it's really knocked down tremendously, and then you either wait--look at that site again like the biblical sites which they dig, and dig, and dig and sometime later starts up again, or a different site starts up again and you get the same phenomenon.



Forget this line, this is the idea of -- the carrying capacity, but you can see nothing fits the carrying capacity. It just maybe stays there for a little here, so the idea of carrying capacity for humans doesn't work very well. What are the reasons--so--then the explanation for the population staying more or less constant and not filling up the space is not that each community doesn't exist, but communities--here's your space filled with community A, B, C, D, E and as each community increases some other community just disappears, goes out of existence. If you measure over the whole big space you have a floating game of different communities each growing, but then disappearing completely, and the population and the whole space stays more or less the same. I don't want to push that as it really becomes super duper constant, but more or less the same--does not fill up.



What are the reasons why a community would grow very happily, more or less, very vaguely, exponentially, and then go out of existence? One is of course climatic disaster. There could be a freeze; there could be a drought, these real climatic things, and if you look at the Anasazi of Arizona that lived near the Colorado [and Rio Grande] River regions, one of the thoughts--they're one of the communities that fit this. They're healthy, you go see their ruins, and then they just disappeared. How many of you have been to Anazasi site in Arizona? Just one student, something you've got to do. There you're living in a semi--a true desert now and a semi-desert back then, so climatic things are a reasonable explanation.



You go into the tropical regions you don't have droughts that last, you don't have freezes, and yet you see this same kind of phenomenon. While undoubtedly climatic things happened occasionally in the temperate zones, certainly in the northern zones, most hunter gatherer societies probably that's not the explanation.



The next thing is diseases of the crops, that some fungus came by and wiped out your crops. Well we've just talked about that, that since they're eating 85 different kinds of things in the desert, there isn't any kind of microorganism that cuts across species like that, so that explanation doesn't seem to work. Diseases of humans, same thing, not diseases of plants, but diseases of humans, again, the data just doesn't fit that, that because of the isolation they don't have a huge problem with communicable diseases.



That leaves the possibility of violent confrontation from one community to another. We've seen in the chimps how the northern group will completely wipe out the southern group and so forth. What kind of evidence can one adduce that this might be what's going on? If one looks at any modern population and looks at the survival curve, so this is the number of deaths per 1,000 per year. This is India, for instance, and it's fairly recent--1960s. Antibiotics are just coming in at this stage, so very high infant mortality rate, 80 per 1,000--one out of every 12 kids dies almost immediately and then that high rate continues until about--comes down to something about six or seven years old so a lot of your population is just wiped out immediately.



Then you have a pretty low level of death and fairly flat until it gets to be what's considered old age in different populations and then the death rate rises. You have this very standard u-shaped curve, and here after you have sort of modern medicine--this is Sweden in the same year as the infant--primarily the main thing is the infant mortality drops like crazy and the old age stuff--everything drops but the main drop is in infant mortality. The idea is--what I just want you to get out of this--we'll see this graph again and again in a couple of times, is that during the adult years the death rate is very low compared to either here or here.



Now if you look at what we can gather from archeological data from hunter gatherer communities, you have a high death rate of kids. Not as high as when you get all these communicable diseases in modern societies, and then you have a flat period, and then all of a sudden there's this big bump. What they call an excess mortality in exactly the young adult years, and then it comes back down again and you get a more or less normal old age situation.



Well what is it that kills people in their middle years? Violence. So this kind of data--again we don't totally--we don't really know the answer, but this kind of data leads you to suspect that indeed one of the major reasons, not the only reason, but a major reason that the hunter gatherer communities and the early archeological communities disappear so suddenly is that they are wiped out by some sort of violence.



We're right back in hunter gatherer times as far as we can tell to what you've seen before of these mass--I've showed you last time these mass graves that are characteristic of this period.



Okay, nevertheless, over the very long scale of time--our period of being cavemen and hunter gatherers lasted hundreds of thousands of years--but gradually population did slowly increase, and as population increases, the land available to people gets less. We talk, I think next time about Africa, which has a culture where land is not a scarce commodity and now it's getting to be scarce, but in their traditions, land is not the scarce commodity, but as the population grows the land per person gets less and then you have to make a more intense utilization of the land and farming gets invented. A big discussion whether it actually was the population pressure that caused farming to be invented or whether that was just some brilliant stroke by somebody that invented--that people slowly figured it out.



They actually can trace the origin of agriculture to--the current data is 11,700 years ago in the Middle East, in Anatolia, what's now Turkey, now eastern Turkey, and it expands on the average from the original sites you can watch it expand and it expands at one kilometer a year. That's the average. Then it eventually takes over the whole world. The number of people, and when you invent agriculture, the number of people that can be supported on one plot of land grows up enormously. We've seen that and so these people become more numerous and so in military confrontations and warlike confrontations, they're going to be dominant, almost no matter what the technology is, no matter what the bravery is, if you have an awful lot more people you're going to wipe out or push out groups that don't have that kind of population density.



Agriculture spreads; in the early days of agriculture you don't know an awful lot yet and you probably have one crop that you really know how to grow. For instance, in the Americas, the big crop was corn that most of Latin America even to this day lives on corn, and the North American Indians lived a lot on corn. Of course in Southeast Asia a great big population, it was rice, and you basically lived off most of your calories, most of your food from one single crop.



That's not very healthy because each crop is missing something. Corn, you may know, misses lysine, one of these essential amino acids and over a very long time the Americans learned to--a rather complicated procedure for boiling it in lime to extract this amino acid from the plant, but until that was discovered they must have been extremely unhealthy.



Rice, you know, is missing all kinds of vitamins and people have very severe vitamin deficiencies if their diet is too much rice. You're not getting a health--in early farming you're not getting a particularly healthy diet and you're not getting the vitamins and micronutrients that you need.



Furthermore, your food security goes down. Again, as I've mentioned, that a virus or a fungus, or something attacks your crops, and that's 80% of your calories and that is wiped out in a year you're gone. Or if locusts come by and eat them up or some insect infestation comes through. Also an increase in calorie availability; you can--more people can stay alive and so you get dense populations. The social structure changes, now previously each person could only get enough food basically for himself and maybe a very small family. As you develop the technology of agriculture, an individual can produce a surplus, not everything he feeds. Well who's going to get that surplus? In an egalitarian society he keeps the surplus himself, his family, and so forth.



But there's other guys that are either stronger and nastier then you and they come in and steal your surplus from you, and they have to leave you just with a small part of your production to just keep you alive because they want you to work for them, and so you get societies now where there are classes. There are people who in way or another take the excess food from the farmer and use it for other purposes, usually their own purposes. They can largely hire military to keep them in power and to protect them from other places. That's a large use of the food surplus which agriculture puts up. Also manufacturers come in; they hire artisans to make beautiful gold objects for them, or to make beds, or chairs or all the manufacturing starts on the agricultural surplus that agriculture brings in because an individual human now can produce more calories than he needs to keep going at a subsistence level.



What you see as agriculture progresses is the hunter gatherer societies are generally quite an egalitarian. They'll more or less have a head man but he won't--or a wise man or an old man, but they won't have authority. He can't order other people around; the community has to agree on some project if they undertake projects at all. As more food wealth becomes available, societies start stratifying, you get social classes, you get castes, and this inequality changes everything about the way humans live.



The congestion in the cities--cities start growing up and then you start getting the spread of these infectious diseases where one person spreads it to the next in large agglomerations of humans. That just gets worse and worse up through the 1400s in Europe when you get the Black Death and wipes out a huge number. That is--as civilization progresses the death rate from infectious diseases just keeps going on up.



Adding all this together and the data we have, is that hunter gatherers--their lifespan is ballpark 50 years. In early agriculture societies that goes down to 35 years, so we're really--and I'll show you data that in a lot of places it's probably even lower than that. We have this situation where humans--not counting violence that humans live--when they weren't being attacked by their neighbors, humans were living very well, the hunter gatherer society; sort of Garden of Eden. Then agriculture comes in and the vast mass of humans become peasants; the land becomes owned not by them but by someone else, and they have to give most of what they've produced to someone else, so life becomes miserable.



There's a lot of thought that the various of Garden of Eden myths--I mean almost every culture has some sort of glorification of a very distant past where people did not have to work so hard. In our culture we call it the Garden of Eden; everything was perfect, then something happened, and after the fall of one sort or another, now it's the sweat of our brow. It's a very nice description of what I've been telling you of the hunter gatherers living in a lush environment--before they're pushed into the desert--living quite well, and however, later on then they have to be farmers, the sweat of the brow. And violence like Cain and Abel is what is the fly in the ointment of that beautiful Eden story.



Now we come to the agricultural period in our historical romp through history. There are some really fundamental issues that you have to understand to understand what was happening with population in these times. There's constraints on human population, and the first was this enormous infant mortality which I showed you. Again, we're looking at 1960 here in a very civilized place, poor India in 1960, but still even into the 1960s where we're very modern, the infant mortality is enormous. You go, even currently, to a less well developed place, just cut out this quote from Haiti in 1979, before this recent rash of problems, a Cornell trained Haitian, comes from Haiti to Cornell, gets a medical degree, returns to Haiti, and he gets a job at a pediatric hospital: "40% of the infants, of the babies," the birth rate--he's working in among other things a maternity clinic, "40% of the babies were dying of endemic diarrhea. A man would come to pick up the bodies three times a day with a big bag. The noise of the skulls in the bag was unbearable." And this is 1979 in--how far is Haiti from Miami? A hundred and fifty miles or something like that.



The data--we have various data sets for what life expectancy was like, and this is various populations and what this is, this is a survivorship curve. So you take--for 1,000 people born in any given space of time, in an earlier period--so this is Cisalpine Gaul, this is Roman times, that's the part of Gaul that's this side of the Alps according to them, Cisalpine Gaul. Out of 1,000 children born, and actually this shows females but it's more or less the same for males, almost immediately half of them die. That's very characteristic of human societies until modern sanitation comes in, which is in Europe 1700s, and in Asia maybe 1900s.



You have this tremendous death rate of children and then it continues at a fairly high but decreasing death rate, and then finally there's very few people left. This is not the curve which showed you the percentage of death in age thing, but how many people are still surviving? At any point in--by age 15 here, this dotted line, only about 40% of people are still alive, 60% have died before age 15. This again is women, so a lot of these deaths in this middle period, by the time--this is the reproductive years, these dotted lines is 15 to 45 or so, I think 50 in this case, which is the years in which women can reproduce and most of the death in females in this period is childbirth itself. In a developing population, in a pre-medical population, childbirth itself is one of the most dangerous things in these years and the death rates are very high from childbirth itself, so a lot of that is female--is childbirth. If you looked a male population it might even be more extreme due to the--probably due to the violence that we've talked about.



Now as times goes on--we're going to come back to this graph, but as time goes on, this is Italy in 1921 and things have gotten--at all ages the death is less, so there's more people surviving, and then you come to Japan; again 1984 and you have very, very little infant mortality, very little mortality through this period and then again old age takes over and people do die. This kind of bump here compared to say this, is again possibly violence in that era, but again, we don't really know.



For our purposes, going back in time, we're really interested in this lower graph which is characteristic of humans from way back until really almost Napoleonic times, maybe through Napoleonic times but the death--the violence in Napoleonic times was enormous. If you look at women, consider this just a graph for women. Of 1,000 women born, 400 are still alive at the beginning of their reproductive period and about 200 are still alive at the end of their reproductive period. If you average that out something like--it would be the same as if something 300 women lived throughout their reproductive period.



Well, if that society is going to keep going, what is needed to happen that these more or less 300 women have to reproduce 1,000 women, right? If they reproduce 1,000 women they also have to reproduce 1,000 boys. So 300 women have to give rise to 2,000 children and if they don't do that then there's fewer and fewer people in each generation and rapidly you don't see this population anymore. How many children is that that each woman has to have? Three hundred women making 2,000 children-- 6 2/3, almost 7, so that means that in--when you have a mortality curve like this, which again is most of human recorded history, most of human history not counting hunter gatherers who did live longer apparently, the absolute minimum that a society could cope with is women have basically an average of seven children.



Wait a minute, I've made this a better case, that's of the--all that this graph shows is women that are alive in this period. What fraction go infertile? What fraction have infertile husbands? What fraction never get married? What fraction are too sick to have children? What fraction of women are worn out after two or three children and can't bear many? That's also a very large number which depends on the population, so if you subtract those--let's call them infertile women for a variety of reasons in which they or their husbands, or their health they're infertile, then there's even fewer people alive and so this curve goes--if you didn't graph just women alive but women that are alive and in childbearing condition, the curve gets much lower, so the number of children that women--the women that were physically capable of it had to have in these pre-modern times was more than seven, and probably eight or nine, or you have to do the calculation and people don't know how to evaluate the--what fraction of Roman women were fertile or infertile? You can't calculate that.



We have a huge problem that somehow there must be cul--there must be mechanisms to insure that no women are wasted, that any woman that can reproduce does reproduce, and when they reproduce they go at it. They just keep going and going, and of course men have an equal part--well they don't do the amount of work but they have a part in it. As I said, this level of mortality continues into quite modern times, it's quite striking.



Europe got out of it a little bit earlier, I say somewhere in 1700s, but for instance in 1912 in Australia--we have an Australian T.A. is she here today? Went to the--she got a ticket to the inauguration--1912 Australian census shows that 60% of all children born died unmarried. That's this number, we have them--well it was about the same number as this, this shows that only 40% are left and this says in Australia 60% are dead, so that's the same number. Sixty percent of children born died unmarried, and among the married one-ninth of marriages were sterile, and just 11% of the men and 14% of the women produced half of the children.



That means those that could reproduce and were married and had to really have very, very high birthrates, as late as 1912. China, as late as 1930, had a nearly aboriginal birth and death rate. The total fertility level was at these levels of six, seven, eight children per woman, yet the population was not increasing, which means the death rate was just as high and they were in this kind of a situation for reproduction. We're going to talk a lot about China later of course.



At that death rate, and this is data for China, in order to have a 50% certainty--so as you know many cultures, and Chinese included in traditional times, for sure wanted at least one child to survive. They do a calculation at this death rate how many children is the minimum you have to have to give yourself a 50% chance of having one son survive; five children. If you're not thinking of reproducing the population, but just reproducing your own family which is the way individual families think, and they have to have a son and you have this mortality rate, at five children you have a 50% chance. If you want to have an 80% chance of something you're back up to eight, nine, ten children which explains the desire--not necessarily--they don't necessarily keep this birth rate but the desire for these very, very high birth rates.



The result is that in most pre-modern societies, women spend their whole post-pubertal lives either pregnant or lactating. There's basically never a time when they're free of the biological aspects of childbearing, not counting the children that are now not breastfeeding anymore that Bonnie was talking about. For instance, in Bangladesh in the 1990s, we're coming up very--75% of the women in the age group of 20 to 39 were either pregnant or lactating. That means four out of every five women were, at that moment, any moment that you look, they're either pregnant or breastfeeding, and there's a small period in which they rest and then it starts over again.



We're not talking--in the need for these very high birth rates, we're not just talking about primitive tribes by any means, we're talking about the period in which all the world's great civilizations developed. Civilization--one of the things that civilizations had to do was insure a birth rate like this. In the period in which cultures were learning to write and producing a classic literature, and developing the great world religions, all of these if you read through them are calculated in some sense to keep fertility high. All of these things glorify high fertility. The religious doctrines push it; there's community sanctions; the cultures just developed in a way that--in order to increase fertility and any culture that doesn't do that and doesn't increase it successfully, they're just not here anymore. Of course most cultures that you read about are not here anymore, and they were not successful.



In our Western culture, the most famous of these things is the First Commandment in the Bible: be fruitful and multiply. Well that fits us, if you didn't do that then the Hebrews would be gone, and we wouldn't have any of what we currently have in terms of religion; any kind of the monotheistic religions. There's all kinds--you look at the culture--the religious tradition of any culture, you'll find all kinds of laws about regulating sexuality.



Now, Yale students don't know much about the Bible--how many of you know--you know masturbation is supposed to a bad thing, do you know what the Bible is supposed to prohibit that?



Student: Story of Onan spilling his seed.



Professor Robert Wyman: Yes, so it's the story Onan spilling his seed, and do you know why he was spilling his seed or what the situation is?



Student: There's different versions, one is that he was having sex with his brother's wife and didn't want to impregnate her.



Professor Robert Wyman: Why was he having--so she said he was having sex with his brother's wife and didn't want to impregnate her; that's correct.



Student: Well he was doing it because his brother had passed away, and according to the Levirate marriage tradition, he was then supposed to do it, in order to have a kid that would--have his brother's kid, but he didn't want to have a kid that would count as the brother's kid, he wanted his kid to count as his kid, so he would always pull out and spill his seed on the ground, and God said that's immoral and struck him dead.



Professor Robert Wyman: Right, exactly correct. I have to repeat this for the camera. The situation--it's a very short passage, a very interesting passage, and it's giving out various moral--it's in a section giving out moral laws, and it says, 'someone had sons and one of them was Ur, and Ur was married, and Ur died.' It doesn't say much about Ur except that he died. Onan was the next brother. Repeated in the Old Testament many times is that if a man's brother dies he has the moral obligation to inseminate the sister--the sister-in-law--in order to secure an heir for the dead brother. That if he fathers a child with his sister-in-law then that is not considered his child, it is considered the dead brother's child, and that's one of these important things of carrying on the family lines which is one of the ways of course insures a high population birthrate.



This is a way of keeping women, whether they're married or not, whether their husband is dead or not, you've got to keep them reproducing or the culture disappears. Why doesn't Ur want to do--why doesn't Onan want to do this? Well he may or may--it's not his kid so it was born--there's none of this sort of power and authority, and macho stature to come with having a lot of kids because it's the brother's kid, in the culture it was the brother's kid, but on top of that he would have to support this kid. Economically he would have to support not only the wife but the kid, and he didn't want to have to support kids that weren't his, so he engaged in the sex act because that was the fun part of it and--but at the last minute he pulls out and spills his seed upon the ground.



Then the Bible passage is very curt, it doesn't say more--and then God killed him. There's not a lot of explanation for this. It's repeated, this particular law called the levirate laws, as a student said is repeated in several places in the Bible and it's very, very clear that people didn't do this. People did not insem--did not want to inseminate their brother's wives because of these reasons and so whenever you see a law sort of demanding something over and over again you know people weren't doing it and that's why the law is demanding it.



That's just one example of how religion gets involved in enforcing fertility, and in this particular example, it's one of the mechanisms for keeping every woman pregnant as much of the time as possible, independent of her state of marriage.



The--anybody know why the Muslims took to polygamy? Why Mohammed allowed four wives; no Muslims in the class?



Student: To free women from slavery.



Professor Robert Wyman: What?



Student: To free women from slavery. Married women--that's the version that I remember.



Professor Robert Wyman: No. The standard version is they were going through a lot of wars. The Muslims were conquering the whole world, they were constantly at war, the men were getting killed. There weren't enough men, so what do you do with the other women? They--I mean many reasons but one of--they need support and so it's a beneficial thing, but their society needed more men, more children, so let them get married multiply. You just--whatever religion you want to look at you'll find similar kinds of examples.



When we get to family planning issues later on, how people controlled their reproduction, one of the major beliefs that the early--we don't really know again, but in the West was that the mechanism people used was coitus interruptus, because it was the only thing they knew about. It's in the Bible, it tells you what you do, it tells you the result of it, and so that Onan passage is currently interpreted to say that masturbation and contraception, all kinds of things are bad, when in fact the passage has nothing to do with that. That's not what that passage is about but that's what it's used for today, but it's been used absolutely for the opposite. People use this, oh that's how I can avoid having children and so it's--culture twists itself about and has unexpected consequences.



Okay, so I've been stressing for you that culture pushes up fertility and up to this high limit. What is the limit of human fertility? We have to evaluate that. There's a very famous calculation of this and it's set by the number of years a woman is fertile, which is generally 15 to 45 more or less, it can be a little bit younger, occasionally a little bit older, but they usually consider 30 or so years of fertility. At that--well if she gets pregnant, she's pregnant for nine months. Ovulation rarely starts again before at least three months, if she's lactating and therefore going through--not ovulating again, there's going to be more months.



If a woman has sexual intercourse it takes an average of five cycles to get pregnant. When we talk about abortion we'll talk about why that is, but if a woman's having normal sex trying to get pregnant, the average is five months before she actually does get pregnant and we'll see where that comes from. If the child dies, fetal mortality introduces a month there--anyway you add all of this up and you get 18 months that--pretty much the maximum that human females can do is 18 months or one and a half years. Dividing--what they usually do is choose 20--any particular woman will probably be fertile for 25 years, divide that by 18 months, and you get a theoretical possibility of 16.7 children. Now how many of you know somebody's who has had more than that? What's the maximum number of children you know about?



Student: I know someone with 18 children.



Professor Robert Wyman: Eighteen; I'm bid 18. Only one in the class?



Student: I think the world record for a woman is somewhere--it's really high, much higher than 18. I thought it was like in the 60s.



Professor Robert Wyman: Oh, no not 60. That's really crazy unless there's some crazy multiple birth. Now with modern drugs sometimes there's multiple, but not 60. This is an unusual class, but as time goes on, families get smaller and people don't remember. The maximum I got out of this class was 24 children. I think it was a Chinese student, I don't totally remember, and that 24 was only two sets of twins, so there were 22 separate successful pregnancies, two of which produce twins, 24 children, one woman.



Even--forget this--independent of this calculation which I've just sort of sketched for you at the--even before the calculation was done and the person who did the calculation knew about it--this is not--here is the--Norway in an earlier set of women which is this set, and a later set of women, and this is the number of children that the women have, and the percentage--the per 1,000 of women that have that number. In the late 1880s the most common number from Norway--again we're talking Norway 1890, we're not talking about anything very primitive, is 10 children. The mode for Norway was 10 children and it goes out to 18, which was the record that someone here knew. There were--of course if you had a bigger assembly you get an occasional of something more.



Student: The world's record it's 69 children.



Professor Robert Wyman: What does it say? Good for him--what--that's something special; does it say anything about it?



Student: She has--



Student: Sixteen sets of twins, seven sets of triplets, and four sets of quadruplets.



Professor Robert Wyman: Okay so it was--what was the total number of--yeah so--okay I was wrong. Send me--both of you send me the reference for that because next year I'll use it.



Now, just as long as I've got this slide up there, look what changes. We go from 40 years later, not a huge fraction of time; we're going to talk about this later in the class. It goes from the mode being 10 children to the mode being 2 children. Something drastic happens in between these two in 40 years, and this is common over Europe. This is just one data set and we're going to talk about that a since it's up here. In this period of time that we're talking about women had this very un--in the mode there's a very large number of children and they far exceeded what's calculated as the maximum.



Let's see okay, the answer is that the biological limit is very high. I'll say 24, you say 69, and we have to read that stuff. In a human population, and continuing for any length of time, the highest well-documented fertility is that of the Hutterites in the 1920s. Anybody hear of Hutterites? It's a Christian religious sect that are an--what's called an anabaptist sect that originated in Europe, migrates here, they're in the upper mid-West in North Dakota and going on over into Canada, and they're very successful in both economic ways and in population ways. They marry fairly early, not extremely early but fairly early. They have a good diet, they're farmers and very productive farmers, and they have good medical care. They engage in sex regularly; they're supposed too, and their religion forbids contraception or abortion. Not only do they have--they obey these rules. Many people have those rules in the books but this is a very religious group and they obey the rules.



Their, what we call total fertility rate, which at this moment you can consider the average number of children that a woman in that society would have was 12.4 children. Nothing--that's high--you think that's high, I saw someone blanch here, as an average, but nothing like the 24 or 60 that we're talking about. This is the highest human population that we have documented, can have that, and it's nowhere near any kind of calculation for a limit.



The most usual limit, and you see a lot of cultures in at least some part of the history where the--eight is current cultures were or historical cultures where eight is kind of a maintained average. In the colonial United States, for instance, for a short time when the frontier was wide open they had a fertility rate of eight children per women, but as soon as the frontier would close in a region the fertility rate would drop. It's clearly land availability had something to do with it.



There's good data for Massachusetts, Concord Massachusetts, very good demographic data there. People had these high birth rates until the frontier closed. What did the frontier mean in 1600s in Massachusetts? It meant like Springfield, these were people living in Plymouth, and Concord, and Lexington, right near the coast and the frontier was Springfield, and as soon as--if they had a lot of children, the children would have to move out to Springfield or somewhere which is 100 miles or something like that and that was beyond the frontier. As soon as the children had to move more than a day's horse ride away the fertility rate drops, so there's something about having the support of your children, really having a group that increases the fertility. As soon as the children will have to disperse and not anymore be of some sort of support to you, or some part of your group, fertility comes back down. No society really has ever come close to the biological limit.



Before we talked about how culture pushes up the birth rate, but now we see that something is pushing down the birth rate, that we're coming to an intermediate level. What's going on is again fairly straightforward and simple. That it was this slide that I want--here is again fairly recent data. Chinese women interviewed in 1981, but referring to their pregnancies which had been sometime in the past and it says it tried to gather data on what was the birth interval of your children and how many of them survived? If the birth interval was less than two years 45% of the children died. If it was between two and three years, 34% of the children died. If it was more than three years, only 19% of the children died.



In every culture and every time and place where we have data like this it's very clear that if the birth interval is too small, the children just don't survive. What's going on with pushing down the fertility rate is that it--especially in situations of poverty where resources are not great, women are not especially healthy, there's no--any kind of medicine available, that if the child does not get a lot of resources, which a large case is milk from the mother is the primary thing--in China there's no dairy products at this time in this social class. It's largely food directly from the mother; the children are just going to die.



The reason that fertility is pushed up from below, is pushed down is not to reduce total number of children but to maximize surviving fertility. What people aim is not to just keep popping them out and having them die. What people aim at and cultures have learned to accommodate to is to maximize surviving fertility. Not total fertility, which is just being born, but maximizing the number of children that are going to stay alive to become adult reproducing members of the society.



Now people have many mechanisms for limiting the birth rate. One that is often quite conscious is breastfeeding; it's a very standard method across many cultures. You've all heard of this, lactation amenorrhea, and many, many cultures don't leave--I mean in our culture a woman can breastfeed a little bit or long, it's totally up to the individual. Many cultures are very strict rules about this. You must breastfeed for at least--and there's a certain period of time.



Among the !Kung of Southwest Africa, which these people speak this click language, they've got all these--you've heard of them. Mothers keep the infant with them at all times, they nurse all day, at intervals separated by only 15 minutes. Bonnie how would you like to have that all day long? Nurse every 15 minutes the child; they sleep next to the mother, and have access to her breast all night long and the nursing continues until the child is more than three years old. By that mechanism, primarily by the lactation amenorrhea, the birth interval among !Kung is four years which fits--is beyond this survival issue. This is the kind of--I talked about Nomads and people that have--fairly conscious--they're probably are aware that this is limiting the births and it's something that they want to do.



When the women go foraging they carry their children--again the !Kung, they carry their children with them until their four years old and while carrying the infant she walks up to 12 miles round trip to--it takes 6 miles to go out and find some food and come back; 12 miles round trip and then in addition to that she carries loads of 15 to 35 pounds. Here's a woman who--being a hunter gatherer is probably fairly healthy, she's carrying an infant on her back, walking around 12 miles, and coming back with a load of 35 pounds of food. It's quite a feat and it's clear that they can't--they're not going to have a second infant, one on the back, one of the hip, this is not a way of improving survival. That's--lactation is one mechanism.



There's many taboos on sexual relations, especially after birth. In many cultures, as I said, a prescribed period of nursing. There's also a post-partum taboo against having sexual relations, and again, another obvious mechanism for birth spacing. If you--again this gets to the degree of consciousness of these methods. If you ask a member of a society that has a taboo they report for instance that sex at that time is very dangerous, a life and death matter.



It is dangerous to mix the man's blood with the woman's, and the man's blood is transmitted through semen. It's a bodily fluid and they don't totally--the biology is not very strong. Their course at Yale was terrible--we'll talk a lot about--not a lot--some, about what pre--pre-education people believe about reproduction and everything. If man's blood gets into the woman through his semen then it also gets into her milk, and then the man's blood goes back into the baby through the mother's milk and this is poison for the baby. That's their version of why they shouldn't--why they have this taboo.



We see this in the evolution of cultures, I mean just as we evolve biologically, of course evolve culturally, that cultures may--will pick up a behavioral pattern for who knows what reason, and they may have no clue what it's 'real' as we see it, it's 'real' purpose is, in this case to space births apart they have some kind of cultural story about it and it doesn't matter whether that cultural story has any degree of reality. If they've picked up a cultural norm that works, the society is still here, and that gets passed on. If that cultural practice does not work, not only reproduction, all sorts of ways, that society is gone. This post-partum abstinence is a major issue, especially in Africa now. The abstinence is up to three years which is--that's sort of the mode of this in Africa.



In addition to limit births, there's another thing which again is a population limitation issue, because we've talked about individual family limitation issues, trying to keep the kid alive. If the village is resource limited they may have mechanisms for keeping the whole population of the whole village down, and so in Africa especially, they have a thing called terminal abstinence. That means at a certain point in life the culture demands that you stop having sexual relations. Very often this is when your daughter has her first child. After that you're a grandmother, and you're not supposed to reproduce anymore. It's interesting what--to prevent--they perceive it as preventing conflicts between their duties as mother and their duties as grandmother, so a grandmother is supposed to help raise the grandchildren.



And there's a lot of biological theory about why do humans, somewhat unique among animals, why don't we just die -- females especially after their fertile period, there's no reason for you to evolutionarily stay alive, most animals they don't have a post-menopausal period. The theoretical reason is the grandmother effect, that as a grandmother you support the children of your child, and that increases their survival, and so it's evolutionarily good. Here in these tribes in Africa, are basically saying the same thing that if you're a grandmother you're going to have a conflict between taking care of your own children and taking care of your daughter's children, and that conflict is bad so you have to not engage in sexuality.



Up to the middle of the 1900s in Ireland, rural Ireland, people lived in households with many members of both sexes and several generations, big multi-family houses. The Irish believe that there should be only one sexually active procreative couple in the household, so they also practice grandmother abstinence. These cultural items are--they may seem a little outlandish to us in our modern day but they were effective. They kept that society going.



Another issue is exogamy, that just like chimpanzees, it's again in most animals, it's the males that disperse, but in chimps and humans it's the females that disperse. The females leave the community at birth, to go live with the man's family, and so she's under the control then, in many cultures basically a slave to the son's family, and the reproductive rules are then set by the son's family and she has no choice in this and we'll talk about that extra--this out marrying--remember with chimpanzees they were hostile to the neighbors around us, human societies are that same way. The professor in the lab next to me is from China, a village near Shanghai, and he describes this to me in China, and he says my village, which have all the same name as him, it's all a male bonded, the males have been there forever, they all have the same last name--they're hostile to all the villages around them so they won't marry the village around them. To get married they have to go two villages away and they're still sort of enemies.



In New Guinea where all over the world that's the same problem, you're fighting with your neighbors, and yet you have to get wives from somewhere, you have to exchange genetic material, otherwise you get inbreeding and so the Mae Enga they say in New Guinea that we marry our enemies and--this is a great story. Time is up; I will continue this story next time.



[end of transcript]

Course Index

Course Description


This survey course introduces students to the important and basic material on human fertility, population growth, the demographic transition and population policy. Topics include: the human and environmental dimensions of population pressure, demographic history, economic and cultural causes of demographic change, environmental carrying capacity and sustainability. Political, religious and ethical issues surrounding fertility are also addressed. The lectures and readings attempt to balance theoretical and demographic scale analyzes with studies of individual humans and communities. The perspective is global with both developed and developing countries included.



Course Structure:

This Yale College course, taught on campus twice per week for 75 minutes, was recorded for Open Yale Courses in Spring 2009.

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