“The Accidental Mind: How Brain Evolution Has Given Us Love, Memory, Dreams, and God.”
An interview of author David J. Linden, professor of neuroscience at John Hopkins University, conducted by Pat Morrison on KPCC’s Morning Edition
Pat Morrison: Over centuries the brain has been regarded as many things not only the seat of reason but the very size of the brain was supposed to be an indicator of how smart or how stupid people were. In the 19th century a pseudo-science called phrenology said that it could predict your personality and your character by the bumps on your head. We know more now.
Pat Morrison: What was it that made you decide to write this book? We hear so much about how beautiful the design of the brain is, an elegant instrument of human nature, however, you are throwing all that out the window.
David Linden: I am indeed. I started out with this book with the intention of writing a field guide to the brain, a guided tour book, if you will. However, as I started writing it, I realized that what I wanted people to realize, however, was that in terms of human evolution, the things in human experience that people hold most central—love, memory, dreams, religious feelings—are not the latest design elements of an impeccably
engineered brain but rather come about through the poor evolutionary design of the brain as has been accrued over millions of years.
PM: The that way you describe how the brain came into being as the way we know it now, reminds one of the car that they drove in “The Beverly Hillbillies.” It seems like little bits and pieces were added on as necessary to make it function.
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DL: Absolutely! A genius inventor didn’t design our brain on a blank sheet of paper.
Our brain is the lizard brain, with some more stuff thrown on top to make the rat brain, with some more stuff thrown on top to make the human brain.
PM: Now Carl Sagan used to talk about the ancient brain, the limbic system, the one that you refer to as the reptile brain. It helps us breath, makes our eyes blink, all those basic functions. Over time, what was added and it what order? Again, to use the metaphor of the car, another California icon, it is like ordering parts to make it run.
DL: The metaphor I like to use is that of the ice cream cone. So basically if you have a cone with one scoop on the bottom, that scoop has the things we have in common with for example, lizards, in other words, the ability to control our heart rate and respiration and take in a limited degree of sensory information. And the second scoop of the brain that includes the limbic system and the emotional centers brings us up to what we share with a lower mammal like a rat. And then what has been elaborated for humans are a set of cognitive abilities that anatomically, we would call the top scoop. This analogy is a spatial one as well as merely a metaphor because it turns out the most recently evolved parts of our brain are literally those at the top of our brain and that is the neo-cortex.
PM: What is it the relationship between what we needed the brain to do and how it physically came into place?
DL: As human we are not particularly strong or quick and our hominid ancestors lived in social groups so basically we had to survive by being clever. To do this we had to have the ability to communicate with each other. We had to have what the ability of what is called the “theory of mind”, that is, to have a sense of what others might be thinking based on events that have occurred. If I can take this to the level of molecules and cells, here is the challenge. The building blocks of brains are nerve cells or neurons and they connect with each other at specialized locations called synapses. Each individual neuron is a very limited processor. It is slow, it is inefficient, and it doesn’t work the same way every time. So if you want to build a very sophisticated computer to do the things that humans need to do, the way the brain has evolved to do this—because it can’t redesign from scratch, it has taken these very simple processors and made our brains extremely
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large by having a large number of these, about 100 billion, massively interconnected.
There are about 500 trillion connections in our brain. Therefore, our cognitive power derives not from having powerful individual processors but having stupid individual processors wired up in a very complex way.
PM: Is it to our advantage that they are stupid?
DL: I don’t necessarily think it is to our advantage that they are stupid. As a game we could imagine engineers building a brain differently with smart processor rather than with stupid ones. However, so much of what shapes us is history. It is what happened during evolution. Neurons first emerged about 600 million years ago in coral and jellyfish-like ancestors and they have persisted since but the design of a jellyfish neuron and a human neuron is not that different. To make ourselves cleverer than a jellyfish we’ve had to take a lot of stupid neurons and wire them together. What has come out of that has been very, very interesting. What I have argued in this book is that love, memory, dreams, and god have all come from this particular evolutionary constraint.
PM: The field of evolutionary biology has been an enormous one over the past twenty years and politically contentious as well. However, things don’t develop in the brain or elsewhere in the organism unless there is a need for them. So what, for example, let’s start with memory, is the need for memory? Why would a brain cultivate that kind of skill or ability?
DL: I like to say memory does for the individual what the genetic code does for the species. Species have their genome encoded in their DNA and through many, many generations they can adapt to their environment slowly through the process natural selection, but that does no good for you as an individual. However, when you have a brain and you have memory for example, and you can improve your behavior based upon your past experience, that allows you as an individual to do what the species could only do very slowly through its genome. So the brain is very adaptive. Obviously, we’ve gotten learning out of this. One of the things that I argue is that learning has come about indirectly from having crummy brain design, so we have to have this big interconnected
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brain in order to have enough processing power then you have the problem, do you have enough information in your DNA to determine the wiring diagram from point to point for all that incredibly complicated set of connections. The answer is no. There is not enough information in the genome to do that. What happens in the brain is that the rough design is laid down in the genome but the fine details of how it is wired up depend on crafting the physical structure of the brain as a result of experience immediately before and
continuing after we are born. Those processes, the ability to change subtly the structure of our brain as a result of experience, initially came about to wire up this complex brain but then they got retained to give us memory. Now if you have the ability to have experience change your brain that is what you need to store memories as well.
PM: So it became integrated. Or circular.
DL: Absolutely.
PM: Is the same thing true of dreams? Is there an evolutionary function for dreams that the brain responded to that caused it to build a “dream response”? Many people have observed their pets moving in their sleep and assume that they are dreaming.
DL: The evidence that supports the idea that animals dreams is very good, however, obviously we cannot ask them. Evidence suggests that animals as low as fruit flies may even dream. The issue of dreaming is extremely contentious in brain research. Some people believe that dreaming has very particular functions that allow you to work out psychological problems or gain insight through the experience of dreaming. Other people believe that dreaming is the smoke rather than the fire so to speak. What is really going on during dreaming is taking our memories during the day and integrating them and indexing them with emotions and with our past experiences. What floats to the surface during that process gets stitched together in our brain to form dreams. While dreams are interesting, and they are related to those things we care about, perhaps they are the smoke rather than the fire.
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PM: You have also mentioned God and I suppose that this is the trickiest part of your proposition. The book some years ago by Francis Crick, “The Scientific Search for the Soul”, expresses the idea a kind of unified field theory that brings together in a physical form, in this case the brain, the distinct things that make us human, in the case of god, the idea of faith. Where does the physical function of the brain intersect with that?
DL: Where does the physical function of the brain intersect with that? Well, that is the million dollar question. The short answer is that we don’t know. The more interesting speculative answer is this: it appears as if our brains have I would call a narrative
constructing function. When we look at information from our senses, we can’t help—it is subconscious—but try to make a coherent story of that. We take fragments of our
experience and we try to make sense of them. It happens in our waking life, it happens in our dreams and I think that it is this narrative constructing function, which appears to be located in the left cortex, incidentally, that is ultimately what gives rise to the cross cultural propensity for both religious thought and scientific thought. I hold that science and religion are really not the opposite of each other. Both of them start with faith. When you are testing a scientific hypothesis to start with you have to believe something that you cannot prove. Then you subject it to a certain set of tests. When you have religious ideas, you believe things that you cannot prove but you don’t expect to subject them to that process. However, science and religion are actually two branches, I believe, of the same cognitive stream.
PM: Why then since the time of Galileo have science and God been seen as opposite of each other when you say they are two branches of a similar impulse?
DL: They come from the same motivation and why they have been warring and continue to war, particularly in the United States, more so than in most other countries is this: there is a lot of fault to be spread on both sides. I think that a lot of scientists are arrogant and think that if we can disprove certain things in religious texts like the biblical 6,000 year old through geology or some other science then we have to throw out all religious ideas.
That is not warranted because science cannot prove or disprove central tenants of most religions such as an immortal soul or a supreme being, On the other hand, many religions
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have been very intolerant of science. They have said that we are going to stick to the literal reading of our sacred texts. Anything that casts doubt on those, we will attack. We do not expect this to be rational, It is the best way to demonstrate one’s faith to just say there is no way you could ever convince me.
PM: What is it about the accidental creation of the brain as we have it now that is singularly human? We have seen patterns in primates that duplicate virtually everything which humans are able to do. Are there one or two distinctions that say that this is a human brain?
DL: No. For example, if we look at a chimpanzee brain, our closest relative, and we look at a human brain, we don’t see them yet as being qualitatively different. They are very, very similar on both a structural and chemical level. And so far, because we now have these genomes in hand, this applies on a genetic level too, although this analysis
continues. There is some emergent property somewhere between chimpanzees and us that happened as a result of humans having more cortex or a slightly different mode of
processing in the highest regions of the brain, but we don’t know what that is.
PM: You talk about each brain being able to use, for example, memory, to be its own evolutionary process to improve that particular person. Do you see the brain as something that is in play to this day? Is a human brain still evolving, adding function, and accretions for the demands for whatever may come across its horizons?
DL: Well, I would say yes, and not just for the brain but for all organisms and organs evolution never stops—neither for liver, or kidneys or any part of your body. The brain is no different in that regard. Evolution is a very slow process. You might ask why are we well adapted to modern urban life. Why isn’t my brain better adapted to listen to my iPod while I am typing on my keyboard simultaneously? Well, these things happen very, very slowly. A lot of our adaptations are for things that happened many tens of thousands of years ago and don’t necessarily apply directly to our modern lives.
PM: To the individual brain, how much variation is there when you go in and look at
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neural functions? For example, looking at gay brains versus non-gay brains. How wide are the variants in the individual human brains and how are they reflected in who the human is?
DL: Well, this is very interesting and controversial question. Human brains, while they have the same general plan, do vary in some important ways. They can vary in their size over about a thirty or forty percent range in normal people. While for a long time it was thought that this had no impact on your cognitive function whatsoever. Recent evidence suggests that your so-called general intelligence as measured by an IQ test about forty percent that can be accounted for by your brain size. However, brain size is probably something that is a very crude measure. What may be more important in determining peoples different cognitive functions and cognitive styles might be something more subtle, for example, the subtle shape of neurons, the particular way in which they process electrical signals. In the end, this may tern out to be more important, but we know very little about it now.
PM: Brain chemistry is personality?
DL: I would say to some extent that brain chemistry is personality but I would say that the most important thing is that it is a two way street. In other words when people hear that neurotransmitters or hormones influence your behavior it is assumed that that is the direction of the causality. But your experience can also change your brain. So if you are treated a certain way in childhood that has the capacity to mold the physical and chemical properties of your brain in ways that are important to you in later life. Causality in the brain is a two way street. It goes from genes and chemicals to behavior and from behavior and experience back to genes and chemicals.
PM: Will people ever be satisfied with the scientific answers they find out about the brain or will they always want to have that elusive sense of human, that characteristic that cannot be define or calculated or put down in a chemical formula?
DL: I don’t think people should expect for biology to explain all the mystery of humanity.
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I think that biology can explain a subset of that. It can tell us some certain things that will illuminate things that are central to our lives, but we should not expect to entirely
understand our humanity in terms of neurotransmitters or brain size or what have you.
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