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So there's this wonderful guy called Carrie Risler. He did a study that basically left the neuroscience community reeling. The grandparents had somehow transmitted this new experience across two generations to impact the behavior of the grandps. Hello and welcome to Instant Genius. I'm Jason Goodger, commissioning editor at BBC Science Focus. In this episode, we're joined by Dr. for Hannah Kritlo, a neuroscientist and author based at the University of Cambridge and recipient of the 2026 Humanist Society's Rosalind Franklin Medal. We talk about everything neuroscience can tell us about the nature of free will. So, Dr. Hannah Critow, thank you so much for joining us.
Thanks for the invitation, Jason. You're welcome. So, today we're talking about free will, the notion of free will. So a huge question to start with but a very important one. Do we have a broad description of what we actually mean by free will you know is there a strictish definition of what we're talking about? So really the primary study in this area came in around 1985 by a neuroscientist called Benjamin Libbe and he was based uh at the University of California in San Francisco. Now what he did was really quite a simple uh investigation. He took some volunteers in a laboratory setting and he attached an EEG machine to their skulls. So he had little electrodes and he was
measuring the electrical activity on the motor cortex which is a band of the brain which basically runs around here uh and instructs movement within the body. So for example, there's an area on this side of the motor cortex which instructs movement in the wrist. And he would ask his volunteers um have a look at a clock that's just there in front of you and instruct your wrist to move uh and notice the time when you're instructing your wrist to move. And what he found was that generally speaking for his volunteers, the electrical burst of activity in the motor cortex that was directing that movement actually came 350 milliseconds before they were consciously aware that they were instructing that movement and then the actual movement came 200
milliseconds after that. So it seemed to be the sequence of event that within the brain the direction of the movement occurred before the conscious awareness that you were instructing movement with your in your body. So the initiation of how you were going to interact with the world actually beca came before your conscious awareness. And from this he summized that uh perhaps we don't have any free will which I think is quite a broad interpretation of the results. uh and there's been, you know, quite a lot of discussion about really the meaning of these findings since then. Perhaps it's just that people are kind of they're having a delay with how they're actually monitoring the time that it's
it's taken for their conscious awareness to register. Um, but you know, despite the different interpretations of these studies, what we do know is that going back across different cultures, across our history as a species, we've always been fascinated with this concept of um, destiny or fate if you like. Um, and this idea that perhaps our life trajectories might be pre-programmed into us. Maybe we're born to be destined to be great. Maybe we're, you know, we have this reason for life that is written into us when we're born and there's no shaking that we've got this story, this journey that we've got to go on throughout our life and that this is written into our biology. Um, and it's an idea that has been very much
investigated through storytelling and more recently through scientific investigation and the results are fascinating, I find. Yeah. So let's dig into some of those then. So I think the first thing that will come to most people's minds when they hear this idea and they want to frame it scientifically would be well our genes are passed on throughout generations. So are our genes playing a role in this idea at all? Yeah. So really um in the last few decades we've been able to peer into the brain as never before and watch as a conscious moving mammal navigates this space interacts with others and makes
decisions in its environment and decides how to interact. And the results are showing us how intricate and sophisticated our brains are. Um, and then at the same time as being able to watch decisions being made in the mind, we've been able to live during this great era of a genomics revolution. So, we're now able to sequence the DNA that we've been given from our mom and dad. And just to put some kind of concept of numbers on this, it's 3.2 billion base pairs of nucleotides that we've been given from our mom and dad in the genes. And so there's something in the region of 20 25,000 genes that we've been given. Um and they're expressed and basically dictate how our bodies are going to be put together um including
our brains. So how our brains are going to be put together. And recently we've been able to start to sequence these um nucleotides, this DNA, this individual blueprints that we've been given from our mom and from our dad that creates how our bodies are put together. But we've also been able to watch as we are created in the womb. So we can start to see how this embryo takes shape, how the brain of the baby is kind of um creating the foundation for thought. We can start to see how 86 billion nerve cells uh that live in our brain and we're actually born with that number of brain um brain cells when we emerge from the womb. we can start to see how those nerve cells are being put together in
that second trimester of pregnancy to create the foundation for thoughts for that baby. And then we can start to bring together those results with the genetic results as well. And what you can start to see is that there's this genetic um signature that goes to shape the neural circuitry signature that you were born with as a baby. when you emerge into this life. And so there's these wonderful patterns of genetic predispositions that you've been given from that DNA code from the M and dad that then plays out in how your neural circuitry is put together for that initial circuitry of thought when you're a baby, very young child. And then obviously your early life experiences will go on to shape and
further sculpt that neural circuitry as you experience different things in life. So that affects your perception and your sense of reality. But nonetheless, we can see that genetic code that you've been given goes on to dictate or uh kind of help shape that basic neural circuitry which creates the foundations for thought. So let's rewind a little bit then and um look at what's going on our brains when we have a thought. You know what do we know about that? You know what even is a thought? So each one of those 86 billion nerve cells that we're born with are actually connected up with something in the region of 10,000 other nerve cells. So we have this incredibly intricate
sophisticated circuit board of around 86 trillion connections within our mind. So, it's incredibly complex and each one of those nerve cells is this really beautiful structure. It's kind of got this star- shaped cell body uh which spreads out with dendrites and um it's called dendritic arbers and it looks a little bit like a tree if you like. So, you've got the arborization all the branches from the tree reaching out. Uh and each one of those dendritic arbers basically has lots of other little sticks on it and leaves on it if you like, but they're actually called sinapses. and they connect up to neighboring nerve cells. And then the tree trunk of that nerve cell structure is called an axon. And that's studded
with pores. And those pores basically pump sodium and potassium and ions in and out of that cell membrane. And that pumping of um charged ions basically creates an electric current because it's a movement of charge. And that electric current zips across that nerve cell to the next nerve cell in the circuit because there's also connections if you like in the root system of the nerve cell as well as the leaf system. Um, and so there's this really complicated, very intricate circuit board with these 86 trillion connections, um, basically passing these electric currents from one nerve cell in the circuit to the next nerve cell in the circuit. Uh, at speeds of around 120 mph, these electric currents, so they're
zipping around the brain really, really, really quickly. Uh, and that is thought. So that's how an idea takes shape. through this movement of uh charged ions and the passage of electrical currents. And now the really interesting thing is that when your brain is being created when you're in the womb, uh that initial circuitry those that basic way that those nerve cells are going to start connecting up to allow that information to be processed, right? To create the root ways in your mind. That's all happening under the instruction of the genes being expressed and those genes are basically handed down from your mom and from your dad and that creates that neural circuitry which is why I'm saying it's the foundation for thought.
Yeah. So having said that do we all think largely in the same way or is there sort of subtle variations from one person to the next due to this? Yeah. So uh there subtle variations. So each one of us and when I was you know I was really emphasizing those numbers there and that's because of the sheer power of this these numbers. So I was talking about 3.2 billion base pairs of nucleotides, 86 billion nerve cells in each one of our brain, 86 trillion connections, right? So if you think about it, the number of permutations, the number of different differences that we can have within each one of us,
there's a huge scope for diversity there. Not just in the way that our nucleotides are put together to create our genes, but also in the way that trickles down to impact our neural circuitry. Um, so if we compared your brain to my brain, there would be huge differences. Uh, I mean there'd be similarities in where like the basic structures are. Shouldn't do that. But there'd be like there'd be lots of differences in terms of um the nuances of those that circuitry. And it's that circuitry that basically informs how we perceive the world, how we create our sense of reality, what information we pay attention to, what information we filter out. Um, and then also when we bring together lots of information from the outside world
through all of the different senses and integrate it, which bits do we place more waiting on, which bits do we really, you know, concentrate and focus in on? There'll be big differences between your brain and my brain and the circuitry that we have because of the genes that we've been given from our mom and dad. And that will help us create different versions of reality, different perceptions of the world. And it will also create different habits in our thinking and different habits in the way that we make decisions and behave and focus. Uh and then this is where it gets to the really beautiful thing. So there's been some lovely studies by um Kristen Utar Frith who are neuroscientists that are based at
University College London and they found that when groups of people get together and freely discuss how they view the world, how they uh create their sense of reality, if they can communicate with each other freely, um then they're much more likely, each one of them, to balance out any biases and then start to see the world in a much more accurate way. So when groups of diverse brains get together, you start to create a much more accurate representation of reality. So in essence, we have very unique individual DNA that plays out in our brain circuitry. It also plays out in the way that we look. So we've got different eye color, different hair color, different heights, different weights. Um but we also have different neural circuitry
that creates different types of behaviors as well. So we've got different idiosyncrasies and different flaws and different strengths in our behavior. But when we get groups of very different brains together, then you start to see the world in a much more accurate way. And then you can start to problem solve much more effectively because you've got a greater breadth of cognitive power with which to play from. So you mentioned there habits and behavior. So this is really interesting. So [snorts] I mean this presumably would help us to predict how somebody's going to respond to a certain stimuli or a certain event. Um you know what can we say about that? Can we learn from studying somebody's brain patterns what
their sort of typical habits of thought are? Is that possible? Um so what you can do is you can now very quickly take uh a DNA sample from someone. So take a quick swab inside the cheek, analyze the DNA um from the saliva and the cells there. Uh and um I think it takes you know less than 30 minutes now to do that DNA sequencing and it's very cheap and what that information tells you um can give you some idea of the genetic predisposition that they might have. So we know from huge studies including you know many people that there is a heritability which means a genetic element a genetic predisposition that accounts for the variance across a population that might be attributable to
their genes that they've been given from their mom and dad and we know that for example as I was saying hair color and eye color and height and weight might have a heritability of around 70 to 90% Today when we look at more complex behaviors like our belief system, uh whether we're going to be extrovert or introvert, for example, whether we might be more likely to be leftwing or right-wing in our ideological kind of beliefs, um whether we might be resistant to mental ill health issues, even how long we might live, there is some information that's held within that genetic sequence that we've been given from our mom and had things like how impulsive we might be, how risk averse we might be. So some quite complex
behaviors there that you can kind of use this genetic and this pre brain profiling data and bring it together to predict with some sensitivity what that person's behavior will be like and what their habits in interacting with the world would be like. Yeah. Yeah, I mean that's really interesting because often um discussions like this the whole nature of um well the whole topic of nature versus nurture comes up but in a way an individual human being doesn't have any saying in either to be honest you know I couldn't choose my parents I couldn't choose my genes I couldn't choose the way I was raised even I couldn't choose the environment I grew up in so you know where does the nature of our own personal free will come into that
yeah as a young child you don't really have much choice, do you in your upbringing? Um, and again, so it's reinforcing the genes that you've been that have been passed down. Uh, so your parents have their there and they've basically given you your biological predispositions from the genetic material, but they're also very much shaping the environments that you're in. They've made the choices for which area of the world they're going to be living in, which school you're probably going to be going to, where you're going to be playing. Um so again that's probably reinforcing their preferences and their ways of thinking and their ways of seeing the world. What we do know is that we all of us learn from our
environments uh to a really high degree and this is what I did my PhD research on. So I was looking at how these connections within the brain uh occur as we learn and respond to our environments. So there's um this beautiful process by which we learn. So as we soak up new information uh a little filipodia reaches out from one nerve cell and um makes a connection with a neighboring nerve cell and that filipodia is like this wormlike structure in the brain. is minuscule, you know, it's um nanometers small. And um as that connection is consolidated from a learned thing into a memory, it becomes much more of a stable uh dendritic spine it's called. And now it's mushroom shaped. Uh and it's got these lovely receptors there that help
to um transfer that electric signal that I was talking about earlier with high integrity uh and high responsiveness. And then that mushroom-shaped dendritic spine can actually mature and change and grow into a heart-shaped dendritic spine and then split into two new connections within the brain. So it can amplify the way that signal is being sent um from one nerve cell to another. So this is a dynamic process that is happening in our brains all the time. So every day we're able to create new connections via this very dynamic, flexible approach within our brain to create new roots by which those electric circuits, those electric currents can zip around our brain to create our sense of reality and instruct how we're going
to react to the world. Now, when we're a very young child, we have a huge amount of plasticity. If you zoomed into a little baby's brain, then you would see that there's huge amounts of connectivity changes that occurring. We've got lots and lots of those lovely Filipodia kind of rooting around trying to make new connections. And we know that babies sleep as well for quite a high proportion of the day and um of the and the night hopefully. And um and that sleep process really helps to consolidate what they've learned during the day into those nice stable uh connections, those memory spines. As we get older, we're still able to have that plasticity, that flexibility, that ability to learn from
our environment, but our scope for that, our potential for that is slightly diminished. Um, so there's more uh learning from the environment that occurs within those young baby brains. But as you say, how much control does a baby have over its environment? So again really um the genes that we've been given from our families if we're being brought up by our parents that have been given us that genetic code is really amplifying some of those personality traits um via the choices that the parents are making in terms of how that child is being brought up. Yeah. So I've heard of a concept called transgenerational memory. So that sounds almost like science fiction. Is there really is there much we can say about that?
Yeah. So, we've been talking really just about the parents, haven't we? Shaping the baby's brain and shaping the baby's trajectory and a little bit of how the environment can then later go on to impact the decision-m of that baby as it grows up. But more recently there's this been this wonderful area of neuroscience um or wonderful area of biology really called epigenetics which has looked at how memories can be transmitted across generations not through any changes in the DNA sequence but via a different mode. Now the initial study in this came uh actually fairly recently in 2014. So there's this wonderful guy called Carrie Risler who works in America. Uh and he did a study that basically left the neuroscience
community reeling. They were really shocked by the findings for this because it's quite profound. Um what he did was he knew that mice love the sweet smell of cherries. So when the sweet smell of cherries kind of uh hits their nose, they [snorts] go, "Oh, that smells lovely." And there's an electric signal which basically zips across from the nose all the way to this region of the brain called the nucleus cumbent which is buried deep in the mouse's brain. And we've got one of those regions as well, the nucleus cumbent. It's involved in our feelings of reward and pleasure and motivation. And so this area sparks to life with electrical activity in the mouse because it smelt this sweet smell
of cherry and it starts feeling very motivated to scurry around and look for this lovely little sweet treat to nibble on. Um and what Carrie did was he went against all that all those evolutionary ingrained cues and signals that have been developed in the neural circuitry of the mouse and he actually paired that sweet smell with an electric shock. So the poor mice got a waft of cherry and then they got a mild electric shock in their environment. And they very quickly after a few iterations of this learned to pair the sweet smell of cherries with a electric shock. And so they started to whenever they smelt cherries tense up in anticipation of a shock coming. So preparing their bodies,
preparing their muscles for this mild electric shock. Um so it's kind of the opposite of Pavlov's dog. It's very like mean experiment, a mean version of that. And what um Carrie did after the mice learned this new way of responding to the cherries um was to just leave the mice be. So at this point they didn't get any electric shocks and they didn't get any sweet smell of cherries. And they settled down and they had a family and the pups also had a lovely life. So no electric shocks but no sweet smell of cherries. And they had a family as well. So now we're talking about the grand pups of the original mice in the study. And at this point, Kerry uh wafted in the sweet smell of cherries. And what he
discovered was that somehow the mice had learned to freeze in anticipation and to exhibit more anxious kind of stressed behavior when they smelt the cherries. So it was almost as though the grandparents had somehow transmitted this new experience down the line across two generations to impact the behavior of the grandpups. Now Kerry was interested in how exactly this had happened. He thought perhaps they had been telling the story of this new association and warning the pups and the grandpups. So he did some neat experiments using IVF and fostering out the pups and he found that storytelling certainly wasn't the mode. So they weren't learning through any communication. So then what he did was he started to analyze the sperm of the
original grandfather. And what he found was that there was a epigenetic change. So there was a change not in the DNA in the sperm, not in the sequence um but in the shape of the sperm um the sperm DNA. So DNA is usually this beautiful spiral staircase kind of structure. Uh and um and then it's tightly packaged because you've got to get I mean for humans it's 3.2 billion base pairs like really tightly packaged into all of your chromosomes. So they really compact it up uh in every one of your um basically almost every one of your cells in your body. There's really tightly packaged DNA. Um, and the way that it is shaped actually affects how enzymes can access it to express those genes. And what Carrie found out was that the
experience of pairing the electric shock with the sweet smell of cherry had actually changed the shape, the packaging of that DNA in the grandfather's sperm. So now the enzymes accessed it in a different way and that affected how the neural circuitry was being put together in the baby's brain when it was in the womb and also in the grandp's brain when it was in the womb and before it was born. So now what was happening was um the uh the root that was going from the cherry being kind of triggering a response in the nose was basically now being rrooted because the neural circuitry had basically the genes had been expressed to change the neural circuitry. So it was now going to the amygdala which is an area of the brain
that's involved in the fear response. So it' been rrooted from the nucleus cumbent to go to the amydala which created that fear and that kind of anxious response in the mice. So basically the memory had been transmitted across in this case over two generations and it had changed the way that it was responding to this trigger of this nice sweet smell of cherries. So, I find that this sort of thing really interesting because personally speaking, I'm really terrified of snakes, but I've never lived anywhere really where there are snakes in the wild. I've rarely seen them other than on television, but they're just absolutely like the mice make me freeze and just, oh no, I just can't deal with them. I couldn't, for example, I can, you know, when people put them
around their necks. There's absolutely no way I could do that. And I was wondering, is that a similar thing? What Carrie and researchers since then have found out is that in sea elegance uh which is you know the little kind of earthworms. Yeah. You actually uh you can transmit these types of signals these traumatic memories these concerns over something in the region of 12 to 14 generations. And there seems to be a similar mechanism. Again, it's this change in the way that the DNA is packaged um via these epigenetic modifications that affect the gene expression which affects then how the neural circuitry is wired together. So there's similar mechanisms that exist in humans. So it might be that uh experiences can be transmitted for
humans in much the same way. I mean there is no scientific consensus within the neuroscience community about this yet. is a very new area of scientific study. As I said, the original kind of study and this just came out 11 years ago. So, um we're kind of acrewing more and more data. But it does seem to be the case that uh memories can be transmitted in humans as well using this similar type of epigenetic modification to affect the neural circuitry. Now when we look at your fear of snakes or for example a lot of people are frightened of spiders um what we know is that for example uh for spiders there's something in the region of 38,000 species of spiders across the world um of which only 0.2% of these spiders
actually kind of uh are any danger to humans. So that's quite a low probability that you should be frightened of spiders, but it's something that a lot of us are. And similarly for snakes, there's something in the region of I think in America they found out that there was 16,000 cases of um humans being like hurt by snakes every single year. But only six people per year die from a snake related injury, which I mean is still fairly high, isn't it? if you consider that from an English perspective, but statistically speaking, snakes and spiders aren't really that terrifying to us. So, is it that maybe going back in our evolutionary history, uh there's some ingrained response that helps to
protect us similarly to this sweet smell of cherries that Kerry was kind of giving. Maybe there's some evolutionary ingrained response to make us more wary of snakes and spiders. Well, first of all, when you look at uh children across different cultures, the way that they focus their gaze on uh snakes, for example, then you can see that they do seem to have a hyper vigilance to them. So, they seem to from a very young age, before we've learned anything through storytelling or from observing other people's reactions, we seem to focus our gaze on snake like objects when there's lots going on in the environment.
Um, but also we know that we can very much learn our responses from those around us. So, for example, when I was bringing my young son up, Max, uh, we were living on a houseboat in the river cam and um, spiders were actually very useful because they used to gobble up all the midgetes. And so, and so when we were living in England on the in Cambridge, uh, Max was showed no fear of spiders. And in fact, we would spend a bit of time looking at them and finding them quite interesting in looking at spiderw webs. Um, then we moved to Australia for a little bit and he very quickly learned that actually you should be concerned about spiders and snakes and then when we returned back to England he brought that fear
with him and um there was obviously a mi mismatch in expectation because a lot of people his friends in England weren't weren't frightened of them at all. So I think it's bit of both is basically what I'm saying there. But there's different modes by which we can create our perception of the world. So we might be genetically predisposed uh to be much more risk averse of certain things from our parents from the genes that we've been given. There's also the stories that have been handed down. um the emotions that we're soaking up from other people uh and their reactions that we're imitating because we're very sociable species and so we do learn from each other. Um and then that on top of that there might be these
epigenetic responses that have been passed down across generations and all of this goes to shape our perception of the world to create a very unique way that we see the world and a very unique way that we interact with it. Yeah. So sort of in a way we're all in well in some ways predetermined to think and act in certain ways but you mentioned there the snakes thing having heard that so I know it's sort of an irrational fear I don't need to be afraid of them but what can we do to break out of these sort of predetermined patterns of behavior and thinking based on this knowledge. So actually Kerry's been uh looking into this quite a lot and with others around the world um following on from his initial studies in
the mice with the cherries and he's done some fantastic collaborations which have resulted in research that have been published in the last year where they've been looking at the power of CBT so cognitive behavioral therapy to actually epigenetically reverse any fears that might have been epigenetically put into our bi biology and into our response. So CBT for example can have a really positive impact um and can actually exert its root epigenetically as well. We pick up emotions from other people and we learn from their perception of the world. And there's some really lovely research that has again it's very recent. Um, so scientists have been analyzing not just the electrical activity that occurs within an
individual's mind to help create their sense of reality. So watching those electric signals zip across the brain across all the different regions in that very individual mind, that very individual neural circuitry that we have. So they've been doing that for over a hundred years now since the EEG was first uh developed. Um, but more recently, just over the last 10 years or so, researchers have been looking at what happens when groups of people get together and what happens to those electrical oscillations when we all start to work together. And we can start to see that those electrical signals start to become synchronized with each other. They start to become in step with each other when groups of brains are working together
well. So when we're able to learn from each other, build consensus to communicate freely without a huge amount of dominance dynamics, when we can start to really balance out those biases in our information processing that we might have um and start to create almost a kind of a hive mind where we've got this beautiful superbrain that's working in step with each other, all lovely and kind of physiologically aligned. And that's when you start to get more consensus building and more innovation as well. So ideas being able to hop from mind to mind so that we can evolve our thinking and innovate and problem solve more effectively. And you can actually use that degree of brain synchronicity
between different groups of brains to predict how well that group is performing and how well it might be problem solving. So how do we use any of the findings from these studies then to inform our own personal choices? I believe that as we start to reveal how our brains operate, how they create our decisions, how they create our sense of reality and our interactions with life, all of this can be used in a very empowering way. So although there's nothing that I can do about the genes that I've been given from my mom and dad and they're very good jeans. Thanks mom and dad, you know, and I, you know, and I can't do anything about what happened to my ancestors, you know, generations
before. What I can do is accept, well, this is the biology that I've got. This is the brain that I have. Um, and perhaps there's particular weaknesses there or flaws or idiosyncrasies, but perhaps also there's strengths. So maybe it's empowering to know the biology that predisposes me to behave in particular way and to then put into practice different ways that my life can be arranged to make the most of those strengths and also perhaps ensure that I'm surrounding myself by people that bring out the best in me and perhaps make up for some of the worst bits of me. And maybe that way of viewing individuality can be useful in raising my son as well uh and be understanding about Yeah. him.
Fascinating stuff. Dr. Hannah Cridgeau, thanks so much for joining us. Thanks, Jason. Thank you for watching this episode of Instant Genius, brought to you from the team behind BBC Science Focus. That was Dr. Hannah Critow. To discover more about the topics we've just discussed, why not check out her book, The Science of Fate, or pre-order her upcoming book, The 21st Century Brain. If you liked what you just saw, then please do consider liking and subscribing to the channel.
