2001 LECTURE SERIES

Why Did Episodic Memory Evolve?

Dr. Endel Tulving
Rotman Research Institute
University of Toronto
January 31, 2001

Dr. Tulving holds the Tannenbaum Chair in cognitive neuroscience at the Rottman Institute in Toronto. For anyone acquainted with research on human memory over the last several decades, no introduction is really required and no introduction can truly reflect his enormous, insightful, and sustained contributions to the field. Dr. Tulving has, through his research and writing, told us much of what we now know about how we retrieve our memories, especially memories for events, and he's called this episodic memory. We'll learn much more about that form of memory this evening.

Dr. Tulving is clearly one of our most distinguished neuroscientists. He's a member of the U.S. National Academy of Sciences and a fellow of the Royal Society of London, the Royal Swedish Academy of Sciences, and the Royal Society of Canada. He's a William James fellow of the American Psychological Society, and he's received many honorary doctorates and a large number of distinguished awards, including the Warren Medal from the Society for Experimental Psychologists and the McGovern Award of the American Association for the Advancement of Science.

I came to Canada when I was 17, and I wanted to tell you about it so that you will not be spending the first 15 minutes of my talk trying to figure out what kind of an accent I have. I have done research in memory for most of my professional life, and most of the time when I come to tell people about it, I know what I'm talking about. Today, I know half of what I'm talking about. The rest, the latter part of my talk is "ify," questionable. I wanted to tell you, because you are not quite familiar with our field and you don't know what it is that people like myself who come here to talk about the work really have in mind in terms of the seriousness of the topic. I will tell you about a memory that is called episodic memory, and when you find out what episodic memory is, you say, well, that's memory. Why do you need to say it's episodic memory? And if you then follow my talk, you will realize that many people think of episodic memory as memory -- William James certainly did so in 1890 when he wrote his classic volume that everybody knows about, Principles of Psychology. But things have changed since that time, and now we have many different kinds of memory and one has to somehow specify them by different names.

I have worked on episodic memory for a long time, and one problem that had bothered me for as long as I have been working on it -- I first wrote about it in 1972 -- is a question of what is it good for? Why do we have to have it? And I'm talking now about the kind of memory that you think is memory, nothing else. And when I tell you what I think it is good for, why did it evolve, as my title says, I hope, this is where speculation comes in. So don't take it very seriously. Remember, this is just an idea. You may like it, you may not like it, but you're free to make your own decision, too. So in that sense, we're perhaps equal, on equal terms.

I will tell you essentially what episodic memory is, how it differs, what some of the ideas are that we have about episodic memory, and then I will come to the question and the possible answer to it. One thing that I recently found out, even at my age, is one can find out interesting things when one reads books and publications by people who know more about things than we do, it essentially blew my mind when I figured it out. Apparently scientists have figured out that the probability that you are here, right now, we all are here today, in this room, at this point of time, my speaking, you listening, the probability calculated very precisely is zero. There is just no chance of that, and ever since I read that, I said, I would like to give up memory research and start concentrating on this question of how is it possible that we are. I am mentioning it because the answer that I am going to give to my question that was said before is, has to do with evolution, and evolution comes into it. There is cosmic evolution, that's what the picture here shows. There is geologic evolution. Then there's biological evolution and there are different kinds of biological evolution, too. And every one of these evolutions contains happenings or events, highly improbable, which, if they had not taken place, the world would be different and we wouldn't be here today. And my story, of course, is going to be that part of the reason why we are here today, in this kind of a situation, is because of episodic memory. Now that's a very long leap from episodic memory or what you know as memory to our being here today. But I could have actually entitled my talk Why Are We Here Tonight?

As you know, the earth is about four and a half billion years old, according to the best estimate. About four billion years ago, that earth acquired the moon, and because of the earth/moon system that we are familiar with, our cycle is 24 hours. We have a day/night, 24-hour cycle. Before the earth acquired the moon, very clever people have figured out, earth rotated at the rate of about six hours. So night would have been three hours, day, three hours, and so on. And whatever life there was, if there had been any life on this kind of an earth, would have been very different from what we know now.

Well, anyhow, so we started with earth a long time ago and it evolved peacefully, nicely. Here's a current scene of the kind you would have witnessed on the earth even if it hadn't been for human intervention and so on. Now humans have come, appeared on the scene, and they have added something to the earth, and these people who do these things are smart people like this fellow, whom you know and have heard about, and other people, less well known. And that takes me then to the fact that many things that we do on earth, including changing it, in ways such as Einstein did and many other ways too, is because of learning and memory. There's a [inaudible] that says you are what you know, and usually everybody knows that what we know, being human beings, we have not inherited through our gene structure, but we have mostly acquired it through learning. We learn something, we remember it, we use our memory, and then we use it. What many people do not realize is that there are many different kinds of learning and memory. Once you point it out to everyone, then they understand. But it's difficult to imagine on one.

There are these kinds of titles, sensitization, habitration, perceptual priming, perceptual motor skills that you know, learning how to ride a bicycle or type on a keyboard, classical conditioning that Pavlov made famous with his talks, imitation -- people are very good at imitation. Little children, six-month old babies you go to them and do like this and they look at it and do like this and you wonder how is it possible for them to do that. Well, it's a learning by imitation. It's controversial as to whether other animals can do that. Some people say yes, animals can imitate too in a way, and others say no. Imitation happens to be a uniquely human ability.

Language acquisition. We don't think that we have learned the language that we speak, not only to speak it and to listen and understand and comprehend, but also more importantly for our civilization and culture, learn it to read and write and so on, but it's all a matter of learning, different kinds of learning.

Instrumental conditioning. This is a type of learning that Skinner made very famous with his rats and pigeons, including pigeons who were playing Ping Pong and so on. And somebody, when I set up this system here says that Murphy is here tonight, and I said not after we tried this system out so thoroughly, and now, he was right. Murphy is here. We are without power. I think next time, next thing, the lights go out. I was worried about this talk because everybody out East, where I come from, knows that California is in darkness, energy crisis and so on. And they didn't tell me that energy crisis begins with my computer. I think that there's a timing mechanism here. It's somebody tells me that I have to start speaking faster.

Well, Semantic memory is a funny name for something that we think of as knowledge of the world. Everything that you and I and all other human beings and all other creatures that we think of as higher animals, certainly all your pets and animals that you see in the zoos and so on, birds and so on, have this kind of memory. "Semantic" sounds like it's something to do with language, but it is not. It's really knowledge of the world. It's a bad term. Scientist end up with bad terms, inappropriate terms, for many things that they doÉbut this is essentially the world as it exists, including some of the things about yourself and so on Ð semantic memory. And I'm mentioning it because we want to distinguish it from the main topic of tonight's talk, which is episodic memory. And this is now a memory system that allows individuals to mentally travel in subjective time, into the past, remembering past experiences, and this is what usually people think that memory is.

My suggestion is that it's a kind of memory system that evolved recently, in phylogenetic evolution, the Darwinian evolution that we know about. It is probably unique to humans. It develops late in children, and it is especially vulnerable to brain damage. There are a number of people in the audience who violently disagree with my idea, that it is something that is only unique to humans. They would like to have many other animals have episodic memory, too, and we'll come to that in a minute. Many people do not know that young children, I mean, I'm talking about one, two, three year old children, who are virtual learning machines, who by the time they get to be three or four year olds, know very many things about the world, do not have episodic memory. They do not remember things the way you and I do. And again, if I had more time, I would give you examples of it, or if some of you are thinking of kinds of embarrassing questions to ask at the end of my lecture from this lecturer there will tell us all these tall stories, well, ask me about why I think that young children don't have it. And especially vulnerable to brain damage, any kind of a brain damage, not just attributable to disease or injury, but also something that happens to older people, degenerative dementia, Alzheimer's Disease. People with Alzheimer's do not have a problem with remembering where they put their car keys or glasses or so on. We all have those problems. They do not remember what they did last night, and that's episodic memory. So episodic memory is distinguished from non-episodic memory now in the sense that in the case of non-episodic memory, we start at some time, something happens, and then I find, too, we benefit from that earlier experience that we had at time one. And we now behave differently than we would have done in the absence of the experience. So, for all kinds of non-episodic memory, and that was my whole list there, time works linearly. That's the way it works in physical world, too. From one point to another, to a third, and so on. What happens at one point in time has consequences for a subsequent point of time in the physical world. There is never any reversal. But episodic memory has that property. And episodic memory, I say, is the only form of memory that does it. No other form of memory has that property. That at time two, we're going to take a mental time travel back into the past. And we can do that over many stretches of time. I will not have much time to talk about different kinds of time today, but I just want you to remember that it is possible to distinguish between different kinds of time. Time is time in the sense that water is water, perhaps, but once you start analyzing it more deeply, you say, well, yes, there is a common theme to it, but really the way time is thought about, used, the role it plays in our thinking and in human affairs, if you wish, it is quite different.

So I'm going to be interested in something called subjective time. Conscious awareness of time. The fact that you and I and other healthy, normal, adult human beings have kind of an ability to think time. In order to be able to talk about it in a specific sense, I have made up this term "chronathesia," sense of time, but it is conscious awareness of time. Aphasia is the same derivation from Greek as we have terms such as anesthesia, no sense, no feeling, somasthesia, bodily sense, bodily feeling, and so on. Chronathesia, sense of time. Conscious awareness of time.

This is another one of my wife's paintings; my wife is an artist. I show that because it gives me a chance to sum up what I've said so far. What I've done so far is to suggest that, contrary to popular opinion, which is that memory has to do with time, most forms of memory do not have anything more to do with time than any other kind of a physical or biological process that we know, such as when you get vaccinated against some disease which is in your immune system and it's effective later on. You're less likely to catch that flu or what not, and whether or not you remember anything about the injection or not makes no difference for the affect. It works linearly from Time 1, cause here, to time two, affectation. You have a meal right now and a drink or two, as some of you, I watched you with my own eyes there in the other room, I did, and so on, even if you forget about that experience, you don't need that experience to have the benefits of having had that. That's the way nature works. And what I'm suggesting that when it comes to episodic memory, things are different, that we actually do have to go back in time to make use of this capability that we have called episodic memory. So, time is one element that distinguishes between episodic memory and all other forms of memory, including our knowledge of the world, what I called Semantic memory, and everything else, different forms of conditioning, classical, instrumental, imitation, and all that. And in none of those cases is remembering the past necessary. Sometimes you may do that, but it's not necessary.

Well, let me mention then the one part of the story or theory or hypothesis or speculation, this is a picture of the branch of evolutionary tree in which we, human beings, are present. It only shows part of it, of course, and it starts with these prosimians and then new world monkeys and old world monkeys, and then the higher apes, gibbons, orangutans, gorillas, chimpanzees, our closest relatives. Here are we, the humans. We last shared a common ancestor with our closest living relative, chimpanzees, some five million years ago, and we have had a long and arduous journey over that time. Now according to the theory that I'm sharing with you tonight, chimpanzees and no other animal here have episodic memory, or not quite the episodic memory that humans do. They cannot remember what happened to them, let's say, last night. But they are very knowledgeable about their environment. They know all about it. Your pet dogs and pet cats know a great deal about the environment. They know that snow is wet and cold and then predict to be avoided and so on. Your goldfish may not know about it, but the pets, the mammals, are very familiar with it. So, I'm not saying that they have no memory, no learning, very important to remember that. They are very capable in learning a great deal about the world. But I suggest that somewhere along this journey, and my idea, suspicion is rather recently human acquired this one additional embellishment on memory systems, episodic memory.

Now, hypothesis is in effect, the hypothesis, tentative idea, you want to argue with me about it and we will have an argument, I will not insist that I am right. I'm willing to listen to you and so on. But the argument is that non-human animals do not have the kind of episodic memory and chronathesia, time sense, that humans do. But at the same time, the absolutely, incontrovertible fact is that they have learning mechanisms in the brain and processes and many other features that are very much the same as those of human beings. So the important thing to remember when you listen to me is that animals and humans have memory and learning capabilities that are both similar and different. You do, we all know we do share a very large proportion of genes with them. Some estimates differ, but it's somewhere between 98 to 99% with chimpanzees. And therefore the idea that episodic memory is one of the distinctly human features is apart from that. I am not denying anything else.

It's very difficult to believe that this human being here doesn't have any episodic memory or somebody who looks so much like a human being. Very thoughtful, it's very easy to imagine that he's trying to think about what to do tomorrow, or how is he going to do in this alpha male who is on the other side of the hill there and doing things that he would much rather do himself. And I don't know whether you can see it, well, I see it very well on my screen, if this fellow is not in deep thought about abstract problems of the world, then I don't know who else could it be. He certainly looks very much more thoughtful than Rodan's Thinker.

Now this is a scrub jay -- Nicki Clayton, who studies them, has made them famous. The Scrub Jay broke into the headlines in science news at least when it turned out that Scrub Jays have something that is almost like episodic memory. Nicki Clayton, at that time, was working at U.C. Davis. Now she is at Cambridge. So, one credit that that scrub jay can take is he helped Nicki Clayton to get a job at Cambridge. The other one is that this scrub jay and others helped Nicki Clayton to do something that had not been done in any kind of animal research before. Namely, prove that these scrub jays not only remember what and where something that had been done over and over in animal research, what happens where but also when did it happen. It's a very clever design, ingenious design, having to do with the fact that scrub jays' preferred food, wax worms, and less preferred food, peanuts, and so whenever scrub jays have a chance, they go for the wax worms. Scrub jays are food catching birds. Whenever they have excess food that they cannot eat, that they want to take it home and cache it in some hiding site somewhere, watching, making sure that other scrub jays don't watch them and so on. And then later on, they have excellent memory -- easily thought of as episodic memory, according to my theory, not just Semantic memory -- and then they go and recovery the cache and eat, use it, consume it when there's no other food available.

And Nicki Clayton and Anthony Dickenson wrote this paper, showing how scrub jays remember not only what was where, what food was in what hiding place, caching place, but also when they had cached it there. If it was only recently, like 24 hours ago, they would go for the worms, because the worms are still fresh. If the caching took place five days earlier, then given the choice, the birds go for the nuts, because they are smart enough to know that nuts are still edible whereas worms, by that time, are yucky. So I was at Davis at that time and I talk about these problems with Nicki and we had lots of discussions about what was episodic memory and whether she had demonstrated it, and in, to her credit, she accepted my argument that they were almost, her scrub jays were almost like human beings in terms of remembering what, where, and when. But they did lack the human component of episodic memory which is what I call autonomic consciousness and also subjective time, chronathesia, and she complained and said, yes, they do have, we can't talk to them, I'm learning scrub jay right now, but making not much progress and so on. It's difficult and therefore, perhaps, we'll never find out whether they really do remember. And that's one of the big stumbling blocks in comparative memory research, when we compare humans and animals. In humans, it is very easy to ask someone, all right, you know where your glasses are that you're looking for because you remember putting them there. Usually, you put them in a particular place. Yesterday, you were just going to this place and the telephone rang and you remember. So that's why you do remember. It's so easy to attribute the same kind of thinking, the same kind of memory to other human beings. But it's very difficult to really find out. When you see a dog carrying a bone today, and then the next day, the dog makes a beeline to the place where it is buried and digs it up, it is almost impossible to resist the idea that the dog remembers what he did yesterday and that's why he is acting the way he is today, because that's the way you and I would do that. My claim here is that the dog does not remember the incident or episode of burying that bone in a particular place. But the dog does not know that the world is the kind of a place where there's a bone buried in a particular place, and that's why he goes there.

So, I remind you, this chronathesia is a big player here. What is chronathesia? Conscious awareness of subjective time, past, present and future. And then I also thought that it's cute to think of it as nature's, Mother Nature's, if you wish, own trick to do, undo one bad mistake, namely making for uni-directional time, throughout. And so Nature says, well, there has to be some way of getting out of the uni-direction of it in linearactive time. Let's endow some of the creatures on earth there with a way of switching it around so they can at the present time travel into the past, which doesn't physically exist any more, and also travel, think about it, imagine the future, which also physically doesn't exist at any given time. We live in a Newtonian, four-dimensional universe, remember. So, what I've said then in the next part of the talk so far is that one strong claim I make, and not many people, not everyone, let's say, accepts that at all, is that there are large similarities when it comes to learning and memory between human beings and other species, including our closest relatives. But that there also fundamental differences, and that the fundamental differences, on examination, turn out to be exceedingly important.

So why do I say these things? Is there any evidence of thought? Well, there is some. Not an awful lot, because this whole line of reasoning, the whole interest in chronathesia or a time sense is not very popular in science, has not been around very long. One illustrious example is provided by a young man whose name is Kent, who's a young man, this picture was taken some 15 years ago, when he was 35. Now he's still living in a suburb of Toronto, he's 50 years old, who suffered severe brain injury at the age of 30, in 1981, in a motorcycle accident, and as a result of which he became severely amnesic person. A severely amnesic person is one who does not remember ongoing experiences, has great difficulty learning any new information, but otherwise is quite intellectually intact. He has language, he can think, he can reason, he can read, he can write, he can play chess, not very well, but he does it. He spends a lot of time playing computer games right now. When you discuss matters with him, there's no problem. He's not very talkative, but he responds. He has nice social manners, polite, even has a good sense of humor and so on. What's very special about Kent is that unlike many other amnesic patients who have been studied and written about in the literature, he does not have any episodic memory. His episodic memory is totally dysfunctional. That means that he does not remember a single thing that ever happened to him in his life. He knows a great deal about the world. He has a very good knowledge of the world. He passes intelligence tests reasonable well. He knows that Sahara Desert is in Africa. He knows if you start traveling due south from Chicago that you end up in Mexico and so on. He can tell you the difference between stalagmites and stalactites and he can tell you that James Bond is really 007. He knows all these things because this is general knowledge of the world, that he shares with many other people. He even knows things about himself. He knows that at one time he had a car. He knows what the color of the car was. He knows what the make was. What he doesn't remember is anything that ever happened to him. He doesn't remember a single trip with the car. I tried very hard. I made up all kinds of stories about him, some of which were absolutely true information obtained from his friends and family, and others are totally made up. And he could not tell the difference between the two. He says he does not remember anything. None of those stories that I made up, descriptions of past happenings, made any sense to him. Here he is in front of his house. He's lived there since 1960. He has no problem with it. He knows exactly what it is. He knows where his room is. Nobody has to look after him. He's not feeble-minded. He's not retarded. He lives with his parents. Both retired. They don't have to worry about him at all. He's perfectly happy, normal. He goes for walks around the place. He never gets lost there and so on. Here he is in front of the building where we tested him for several years. He would come in from time to time. And he's pointing at that building because I asked him to do that. Kent, point to the building. But if you ask him, as I did at that time, what is this building, he has no idea because that building came into his life after his accident and he cannot learn anything new.

Now what happened to Kent was that among other parts of the brain that were damaged in this case, is this structure here, called the hippocampus. This little sketch shows some of the important structures in memory, and these are important structures for both episodic and Semantic memory. Hippocampus, hypothalamus memorilary body and then sort of fiber attached, connecting memorilary bodies and hippocampus called the fonix, and also Jim McGaugh and his students' love object here called amictala. If you ever hear him talk about amictala, now you know where it is.

There's nothing wrong with Kent's amictala, but his hippocampus is largely atrophied. He has, roughly speaking, 30% of the hippocampus volume in relation, in comparison with a normal, age, height. So because he has other lesions, other damaged parts of the brain too, we cannot say anything about the particular role that hippocampus plays in this syndrome of his, namely very, very dense anteriograde amnesia, excellent retrograde memory for general knowledge and no remembering from any period of the past, either before the accident or after the accident. Here's an MRI image of his hippocampus. You can perhaps see if you're, a very, very small area left in comparison with an age mate here on the right. So this is one case now where there's a clear distinction between one's ability to know things that severe brain damage that he suffered did not do too much damage, some did of course. But not too much damage to his general knowledge of the world. But did actually literally wiped out or made unuseable his episodic memory.

We have done studies with him where we teach him new information and we can do that. He comes in and we teach him little nonsense sentences such as dog confronted bull dog, or rays softened asphalt, sort of meaningly descriptions of the real world. He can learn those things to the extent that when we give him the first two words of the sentence, he can complete it. He, of course, does not know how it is that he knows, because he does not remember ever having learned anything. And when we ask him what do you think of other people, let's say if we asked him complete the sentence, rays soften, what would they say? Is it asphalt? How many people would say that? A few, some, most of them, just about everybody. He says, just about everybody, because it is his repertoire, and he has no reason to believe that others do not have it. And remember, the claim is now that animals cannot do that. Okay.

The point then is, well, let me go back here. The point I want to make is one really does not need episodic memory for a great deal. Even, I mean, all those animals that I mentioned have no episodic memory, and they're very excellent survivors. Have been, generation after generation. Of course, species do go extinct and others are created or emerge. But, nevertheless, just about no species out of the million or that we have in the world, that are in existence or so, needs episodic memory to be able to exist and to survive. And even we, normal, healthy human beings, do not really rely on episodic memory very much. When you listen to me and try to make sense of what I'm saying, you do it totally in terms of your Semantic knowledge, your understanding of the language, of the concepts, and ideas and so on. You don't have to think back to any particular incident. You can do that for something that you read about or listen to or so. It may remind you of things. That means that you're switching to the episodic retrieval mode. That's all right, but it's not necessary.

And again, as long as Kent lives, he has no problem whatsoever. As long as somebody fills the refrigerator and makes sure that's no California-type energy crisis and just switch on the light and it actually comes on, as long as it's a stable world, he doesn't need episodic memory. He's lived there 20 years. As a matter of fact, he's not quite aware, he's not usually aware of his deficit to begin with. When you ask him, then he does become aware of it, and then he's concerned about it. He frowns and worries about it. Then you distract him for a few seconds and life goes on. If you ask him about his life, I have done so in front of the T.V. cameras, and as a matter of fact, it's been recorded, I say, well, tell me what do you feel about life? Is it, how would you rate it on a five-point scale. One is very bad and five is very good. And since he's a person of understatement, he says, well, four, I guess.

So, if episodic memory is not really very useful, many people, many species can get along without it, why did it switch in evolution? Well, there have been speculations about this. People say, well, it provides a good basis for action. But so does every other form of memory. If you have knowledge acquired in the past that is useable at this moment, in a particular situation when you have to solve a particular task or engage in an action, you can rely on your knowledge, learned knowledge. So episodic memory is nothing else. Some people have suggested that social relationships, when groups of people became larger so that it was more than a roving band of ten or 12 or 15 or so on, one had to keep track of who was friend and who was foe, and how they acted now or recently and before. It has been argued that episodic memory helps us to update information. Semantic memory is okay to pick up information, but to change it and to learn something different from what we've known is not so easy. That's why amnesics who have problems with episodic memory, some amnesics have problems with Semantic memory too, as I said, but they usually do not know. I mean if you go into an amnesic person today and asked who's president, and he may, depending on the age, may say it's Nixon or he may say Carter or he may say Clinton, and very few of them will mention George W. Bush. So that's sort of contra interference. When I go into and say, well, if you've witnessed something in your own eyes, that increases your confidence of that information acquired is really so. It's very difficult. It's true. And you're much more difficult to disuade. But, this wasn't the case if you use your episodic memory and remember it or so. You're perhaps somewhat more likely to listen to arguments against the derived knowledge of the sort that you get in Semantic learning. And there are arguments that it facilitates learning. Semantic system can acquire information all right, but in order to really speed it up and so on, you need this additional system.

There may be something to all of these, and I think an argument can be made for any one of those to a smaller or larger extent. But my idea, and this is the thesis and just really the take home lesson, if you wish, of my talk, is that episodic memory, autonomic consciousness and chronathesia were drivers of human cultural evolution. The idea is that the kind of culture that homosapiens have created over the last 40,000 years or so can be produced only by a species who's mental resources include conscious awareness of the existence of the future in which individuals and their offsprings will continue to live and survive. You have to have an idea of tomorrow in order to deliberately act today in preparation of that in the absence of a stimulus present in the environment that would impel you to do so. And that's an argument that many animals, other non-human animals, who act as if they were preparing something for the future do because they have learned to do so and their stimulus, instigating stimulus is present right now. In human beings, this is different. You don't have to do that.

So what is culture? Culture is one of those terms that is almost difficult to define or impossible to define, as this little example tells you. Half a century ago, these anthropologists identified 164 definitions and they thought that perhaps a common trait to many of them was a culture referred to a social transmitted heritage and concrete patterns of behavior and artifact. But I'm a hard-nosed scientist. This kind of thing confuses me. I don't know what to make of 164 different definitions. I have an idea of what episodic memory is good for, why it evolved, because it helped to get the cultural evolution initiated and maintained. And therefore, I define culture very simply which is a difference between the world as it actually exists and as it would have existed if there had been no changes brought about by the creative human intervention. So I imagine that if it hadn't been for the human brain, the human mind, something to which rather recently, we would live in kind of a natural world, a product of cosmic evolution and the geological evolution, of course, and so on, and also the Darwinian phylogenetic evolution on our earth. And then cultural evolution is simply all those events that brought about the culture as just defined. So we would have lived in a world untouched by human hand. It would have been pristine, beautiful, as it is in parts of the world here now. And then it was humans who started changing it. The idea was very simple. Rather than adapting to their world as it existed, as all other species have had to do since time in memorial or else it perished, Charles Darwin told us all about it, almost 150 years ago, if you wanted to survive, you had to adapt. The world as it existed called the tune and the members of the species who wanted to survive danced to the tune. Once people started realizing that there's a tomorrow and we can do something about it, we started changing it. We started to fit the world to suit their own purposes, to facilitate this business of survival. So the world changed.

Just a few examples of, you can well imagine, I could stand here for months on end and show you pictures of it, and you can only see concrete artifacts. You have to think of human thoughts and stored knowledge about the thoughts, creativity, that lies behind it and is part of the world. Some of you know about opera and Heckles's three worlds: world one, physical artifacts, physical objectives and space, world two, and it's human mind essentially in world three, creations of the human mind. There's a great deal of world three behind these pictures, too. All started, of course, very slowly, some time ago. One can trace it back to much larger than the 40 practae that I mentioned of, which is a pure guess, of course, on my part. And so it goes on and on and on. So remember this is a thesis, my idea. This is where the speculation comes in. Totally untouched. Not peer reviewed. You're the peers now. You make up your mind. You go and find out what it is.

Other ideas have been proposed to account for cultural revolution all the way from physical attributes such as bipedalism, and opposed thumbs, to some of the things that have to do with the mind. But usually people, paleoanthropologists and other people who are worried about the question or how did the human culture as we know it evolve, have stayed rather clear of the mind. They like the brain. Our brain is almost three times as big as the chimpanzees now. And so that must have something to do with it. But as you well know, the brain itself possibly cannot do anything by itself. It's the expression of the brain, the mind, thought, consciousness and the translation of all those thoughts into action that lends the brain credibility as an important part of the network.

So why do I talk about it? What's evidence? The most important piece of evidence I submit tonight, here, to you, is a thought experiment. You think what it would be like, what it could have been like, if our predecessors, ancestors, would not have this ability to think future, to travel in time. Not just into the past, to remember things, but the more important part, into the future, and put yourself in that position too. Suppose you know everything you know about the world, as it exists today. You have all the skills, all the knowledges, and you don't know that there's a future. You would live very happily as Kent does in his world, that's all. But it would be very unlikely that you would do something to improve it, change it in any way, because you don't know that this is necessary, that there are possibilities for exploring it in terms of observing child development and so on. Stanley Klein and his colleagues at University of California Santa Barbara recently studied a patient, an interesting patient, who knows all about the past and the future as long as it pertains to the world, things other than himself. He has no knowledge and awareness, or very little knowledge and awareness, of his own past and has no idea what he's going to do in the future.

Functional brain imaging is another promising technique, because the whole idea is rather new. Nobody yet has done any studies, functional neural imaging, studies of chronathesia. We're starting one now and so on and so on. But a little bit of encouraging evidence or at least idea comes from existing studies that already are available, and here's a summary of one such study. As a matter of fact, it comes from our own lab, by a team led by one of my post-docs, Martel LaFage, who is now at McGill, where we took data from some four experiments that had been done in which we had compared remembering, retrieval of previously learned information, and we're looking for regions in the brain that would show activity as we see here, such that under conditions where the brain would light up when that person is trying to think to something that happened in the past, regardless whether the experimental subject was successful in actually remembering something from the past or not.

Now these retrieval successes and retrieval failures were identically activating brain regions in certain parts of the brain. And these, we've identified six such sites. We call them retrieval mode sites. They were all in the frontal lobes. This, these are the views of the lateral side of the brain, right side of the brain. The numbers here show the distance in millimeters from the midline. So, going laterally from the midline. This is a structure called anterior cingulate, and then there are other structures down there, other paths into the left side of the brain to large regions here. These are regions that show particularly strong activity when people are essentially time traveling into the past. We don't know what the particular functions are of each of these regions. But the speculation is that if the theory that I've been talking about here is right, then some of these regions should also show up when we do a study, when we make people think future or anticipate happenings in the future rather than past. So this, just very quickly, shows that there are ways of finding out what the brain does when the mind engages in this chronathetic activity that I suggest is such a human characteristic. Is this a theory too? Who knows. It is a relatively recent idea. In science, you come up with ideas and you take your chances. So science is a self-correcting enterprise, and there are lots of critics around who will make sure the correction is much faster if you're wrong and they're right. And when it is otherwise, you know about that too. So, I have not published anything on it yet. It's really new. And we'll soon find out what the critics have to say. Since we're talking about the distant past, no absolute proof is ever going to be possible any more than it is possible, absolute proof, let's say for Darwinian Theory of evolution. We've talked about this scheme at least where there's very little contrary evidence available. Since it has not been explored very thoroughly, it is not surprising that I have not been able to think of some contrary evidence. And then final proof of if this kind of theory is uncontravergence in consistency, what sense does it make and so, it would certainly provide all kinds of guidance for future research.

So, to answer the question, why did episodic memory evolve? Episodic memory, the only memory system that allows individuals to mentally travel in subjective time, probably evolved not because it allows such time travel into the past, but because it allows mental time travel into the future. Such proscopic, forward-looking, chronathesia may have been one of the central drivers of the evolution of culture. Thank you very much.