The human brain is seven times larger than it should be for our body size and uses a quarter of our daily energy intake. by your own count, it contains 86 billion neurons and displays the most amazing cognitive abilities. however, you still say that the human brain is not special and that we should not think of it as being at the pinnacle of evolution or at the top of an evolutionary tree. can you explain why?
yeah, I mean it’s not extraordinary, it’s literally out of the ordinary. to be extraordinary, it would have to be built not according to the rules that apply to any other brain, which would be really strange, since we know that there is a basic biological background from which life doesn’t really deviate too much, because the rules are inherited. still, when I became interested in this field of what we call comparative neuroanatomy, there seemed to be a consensus that the human brain was an outlier in many, many ways: its size was proportional to body size and its genetic makeup. and their metabolism, maybe in the genes that built their synapses, and what I realized learning about this (I guess maybe it helped that I had no experience in the field, so I really had to start from step one) was you don’t really understand the basics.
You are reading: Best books on the brain
We didn’t know how many neurons or cells made up different brains, much less the human brain, so we couldn’t really compare the human brain to other brains. that was the work I started doing. and it led to this realization that the human brain is not special, in the sense that it is not an outlier compared to other primate brains. It happens that, being primates, we manage to put many neurons inside this relatively small brain, and through a technological trick that our ancestors devised, processing food before taking it to our mouths, that is, cooking, with or without fire, we manage to gather the largest number of neurons in the cerebral cortex of any species. our brain only appears to be larger than it “should” be when compared to other great apes. It turns out that for a generic primate, it is the great apes that have a brain that is too small for their bodies, and for energetic reasons. they can’t afford both. our brain is as large as expected for a generic primate that is not a great ape. so we’re not special in the sense of being outliers, but we’re still remarkable in our number of neurons in the cerebral cortex, the largest in existence, and which no other species can afford.
The first book on his list is connectome by sebastian seung, which talks about one of the hottest topics in neuroscience, the idea that we might one day create a complete wiring diagram or map of the connections in the brain . tell us what we can learn from this.
One of the things people say about the human brain is that it is the most complex system in the universe, essentially because the number of synapses [connections between neurons] in the cerebral cortex is supposedly the largest. we have yet to figure out exactly how synapse numbers compare between species, but even so, their synaptic connectivity requires an impressive amount of information to describe or configure, and not that much information can be found in the genome itself. there are not enough genes, even by a combinatorial code, to specify all the possible connections between neurons in the cerebral cortex. so connectivity in the brain is initially set up with the basic biological instructions in its genome, but once it’s done, it changes through a self-organizing process. how you use your brain directly specifies what your brain looks like.
“You become more and more of yourself as life goes on.”
that’s the idea behind the connectome as sebastián describes it: this highly personalized set of connections, this pattern that defines who you are. over time, it becomes more and more personalized. you become more and more yourself as life goes on. as your brain moves, it is modified by its own activity. Which more or less answers the question, or resolves the paradox, of how it is possible to get this tremendous amount of complexity in the organization of the human brain with only a handful of genes to configure it. this self-organization of the brain defines its own pattern of connectivity and, in fact, defines the system. your brain contains all the information it has ever lived.
connectome is beautifully written and very accessible to the general public. but no discussion of the remarkable nature of the human brain would be complete without a discussion of consciousness. you have chosen the feeling of what happens of antonio damasio to deal with this topic. what do you like about this book?
What makes Damasio that I find so outstanding is that he goes to the trouble of finding a useful definition of what consciousness is. something that people before him used to be very coy about, because everybody knows, everybody has a conscience, so we all know what we’re talking about, so why bother? I think damasio is correct that the first important step in science is to define what exactly is the question at hand. If you want to talk about consciousness, you first have to define what consciousness is. Damasio actually offers definitions to what he proposes is a nested series of levels of consciousness. It starts with what I think he calls proto-awareness, which is the most basic representation of your own body, through to self-awareness, which he refers to as the ability to represent your brain activity as it represents the body.
As your brain maps not only the body, but also its own body mapping process, he proposes that you gain self-awareness, which is the basis of what we call perception. eventually it comes to autobiographical memory, which is essentially your self-awareness over time, allowing you to get a sense of where you’ve been, how you’ve felt, and where you expect to be over time, and then eventually to self-awareness. moral or social conscience, which is where you fit into the larger system of other people’s conscience as well.
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What’s really cool is that he not only proposed all these different levels of consciousness and types of consciousness, but he also reviewed the anatomical evidence that maps each of these different levels to a nested system of structures in the brain. and so, in the end, what he had was something that actually made sense and was not only supported by evidence, but offered testable hypotheses about the different types of consciousness: what parts of the brain are required or necessary or give rise to the different types of consciousness. levels of consciousness. ; how things should fail when there are problems or interruptions at different levels of the system. I think his book was really groundbreaking and a real turning point for neuroscience.
Does this support your description that the human brain is remarkable but not necessarily unique, in the sense that these ingredients or levels of consciousness and the structures that produce them could be found in other animals?
yes, absolutely. I think he helps organize ideas about how we compare to other species because essentially what he’s saying is that if you have these brain structures, you’ll have at least some level of functioning of these different types of consciousness. and of course the higher the processing power, so the more neurons there are in these different structures, the more complex their cognitive functions or function at that level of consciousness should be. Because we know that the structures in our brain are very similar to the structures found in any mammalian brain, it really leads us to the idea that we’re not talking about quality issues, but quantitative differences between brains. once again, we are not special. we are remarkable, yes, in the level of complexity that we can achieve in all these different levels of consciousness. but we are not outliers.
The next book on her list has a cover review by Nigella Lawson, and is about the Kitchen: Catching Fire by Richard Wrangham. What does cooking have to do with the human brain?
Basically, what Richard is proposing in his book is that the turning point in the history of human evolution was the invention of the kitchen. To my knowledge, he was the first person to propose that something seemingly so simple, so prosaic, could have played such an important role in our evolutionary history. we’ve added to your story, because according to our calculations of how much energy bodies of a certain size with brains of a certain number of neurons cost, then we wouldn’t be here if it hadn’t been for a drastic change in calorie counts by our ancestors. they could get. I think he’s quite insistent that the main change was cooking with fire, hence the title of his book, On Fire.
“If you don’t eat enough calories, your body will start to break down to feed the brain first.”
I think today we have more information that of course once you modify food with fire the change is tremendous but even before using fire to modify food became a habit you just use tools to break down or modify food: crushing, cutting, turning into mush, as our ancestors did with stone tools, also helps enormously to get more calories in less time. I use ‘cooking’ in the much broader definition of any food processing before eating, and in that sense, I propose that cooking was the technological revolution that enabled the rapid expansion of the human brain. a human brain needs about 500 calories in a day. And that’s a very strict requirement, in the sense that if you don’t eat enough calories, your body will start breaking down to feed your brain first.
Do mentally demanding activities consume more calories?
well, that’s the thing: surprisingly, no. that’s about 500 calories no matter what. whether you’re just lazing around all day or solving hard problems all day, as far as we know, you’re using the same total amount of energy: as the brain increases activity in some places, it increases it below in others. but that is really the most intensive use of energy in your entire body. those 500 calories represent 25 percent of your total energy requirement for the day. which is another thing that people used to think was special about the human brain. no other brain that we know of costs relatively as much energy compared to the body. but actually it turns out that it’s just what you’d expect because of how many neurons we have, and because we’re primates, with more neurons in the brain relative to the body than any other mammal we know of so far. so that really means that our brain consumes as much energy as expected for its number of neurons: it’s not special in that sense either.
“There is a very clear metabolic barrier to how big a primate can be. With 8 hours of food a day, that wall is around 180 kilos of body mass.”
We did some math on the trade-off between how many more calories the body needs as it grows and how many more calories it can actually take in as it grows, and it turns out there’s a very clear metabolic wall for how big a primate can get. at 8 hours of eating per day, that wall is about 400 pounds of body mass, and that also limits how many neurons you can afford in your brain. by our calculations, gorillas and orangutans are right next to that metabolic wall, living on the edge of what they can afford, so they couldn’t possibly have a brain with more neurons than they already have. in reality, it is their brains that are too small for their bodies, which makes ours seem too big, when in fact it is not. According to those calculations, if our ancestors ate like other primates do to this day, an unmodified raw diet, an ancestor with a composition similar to that of modern humans, with, say, a 60 to 70 kg body and a brain with 86 billion neurons. I would have had to spend almost nine and a half hours a day eating. which is not feasible. we would not be viable.
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That’s where richard’s idea comes in, that once you have the ability to modify the foods you eat, you can multiply the number of calories you get per unit of time. that means that having a large number of neurons is no longer a burden, something that puts your life in danger; actually, on the contrary, once energy is no longer limiting, having more neurons is likely to become an advantage. you can use those neurons to do something more interesting than just finding food, and now you have time to do it, because eating cooked food requires much less time and effort than eating raw food.
so, continuing with a theme about the importance of the body to the way our brains have developed, your fourth choice is the history of the human body. an interesting choice in a list of the top five books on the human brain?
well, dan lieberman puts the brain in the context of the body as a whole. he’s a friend of richard wrangham, but i know you disagree on what exactly was the first factor that actually enabled such a sharp increase in brain size in human evolution. richard just cooks with fire, while dan argues that it happened too late and talks a lot about broader changes in the human body that also set us on the path to becoming what we are today. that includes the changes that allowed standing. a bipedal primate uses a quarter of the energy to move than a quadrupedal primate. walking upright is slower, but it also costs less energy, so it’s more efficient, and proposes that standing was actually one of the first components that allowed our ancestors to get more food in their day, simply because they could explore ranges wider.
“A bipedal primate uses a quarter of the energy to move than a quadrupedal one.”
couple that with other anatomical changes in the body that lieberman explains in his book, such as changes in the gluteus maximus (butt), toes, neck muscles, and head position, which contribute to make human ancestors very good runners. and once you run you also get access to this new strategy for getting food which is cooperative hunting and that encourages the development of new tools and also communication between individuals which requires more processing power so supposedly that would create a positive selective pressure for more neurons in the brain. you also become able to get more energy through hunting, by running over other animals, so it brings all those things together and makes a very good case for the beginning of human evolution and the rapid increase in brain size. /p>
also gives an answer to the question of how it is that only humans cook, and not other primates, because there were all these other anatomical changes that happened only to the ancestors of our species, and it’s only when all those changes were unite. that you have a species that is not only anatomically capable of standing up, using its hands, and providing enough neurons to have the required processing power, but also has the technology developed along the way and new problems to solve with it. in the rest of the book, he goes on to talk about how, in a modern context, where we live in houses, we eat a less varied diet due to agriculture, we use cars and not feet, we have refrigerators with lots of food, how these anatomical features actually have consequences for our health. it’s a really fascinating book.
The last book on his list takes on one more thing that has traditionally been considered uniquely human, but is just beginning to be considered in other animals: culture. tell me about the secret of our success by joseph henrich.
I think what joe’s book does beautifully is build on an idea that I mentioned in the last chapter of my book, which is that a number of neurons is necessary but not sufficient to explain our abilities, because all the things that we They like to see how our main skills are transmitted culturally, they have to be learned. we are not born with all the knowledge or skills that we have as adults; we are born with abilities and we have to transform those abilities into real abilities. that’s where cultural transmission comes in.
He gives this beautiful example of hordes of elephants where the only ones who could survive a drought were those with females old enough to have survived as young a previous drought 30 years earlier, and had the memory of where they were the other waters. the holes were back then, and they pass on the knowledge to the next generation. you need to acquire that kind of knowledge through experience, but more than that, we have the ability to develop new technologies and new systems to solve problems and also pass on those new technologies through culture.
“how you use your brain is at least as transformative as the biology you were born with.”
I like to ask people how much of what they see around them they could build themselves. take my desk: I could make very crude, very rudimentary paper, but even with my Ph.D. and dozens of years of formal training, I wouldn’t be able to make a single pencil to write on that crude paper. I think that shows the difference between, firstly, our biological abilities, secondly, our abilities that we can turn those abilities into through learning, and thirdly, all the things that we can do but that require cultural transmission of technology. we as a species have that technology, that culture, but each individual person no longer has all of that. we have far passed the point where a single person could possess all the cultural knowledge of the species. I think it’s a very sobering experience to realize how much of the world we would be able to recreate individually.
That’s where culture and the cultural transmission of technology comes into our evolutionary history, which, by the way, is a very strong argument for keeping people educated about science and technology, because the day we lose this knowledge, all that we have so dear as the high achievements of the human species, that everything goes. we have become much more than the number of neurons we have. biology gives you the basics, the starting point, but how you use your brain, what you do with the brain that you have, that’s at least as transformative as the biology you were born with.
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