human evolution or more specifically human brain evolution began hundreds of millions of years ago in creatures with simple nervous systems the brain may have originally been needed for coordinating and governing the organs of the body our brain's evolutionary history can be seen in the heads of species ranging from fish to primates some of the most distinctive functions of the human brain are found in the cerebral cortex but certainly in other brain areas as well the behavioral differences between men and women are partly a result of the fact that male and female brains evolve slightly differently and even mental illnesses like anxiety and depression may have their roots in evolution by natural selection now in this video we'll explore human evolution by focusing on the evolution of the human brain if you are new to this channel i'm andrew cooper sansone and this is sense of mind this channel is dedicated to making neuroscience and psychology simple and clear make sure to subscribe and consider joining our weekly video newsletter by going to senseofmindshow.com newsletter to sign up for free now without further ado the evolution of the human brain [Music] like all things biological the brain has been shaped through evolution by natural selection over eons in the history of life in considering the evolutionary origins of the brain remember that there were bodies before there were brains the neuroscientist antonio damasio argues in his book the strange order of things that the brain and nervous system evolved as servants to the rest of the body in order to help the organism stay in conditions that allow it to flourish that is instead of the body being a slave to the brain it may have originally been the other way around demacio notes that the nervous system of the digestive organs the enteric nervous system also sometimes called the second brain appears to function somewhat independently from the head brain since regulating and coordinating digestion is complex yet also fundamental to survival it's not hard to see how a species that evolved this type of coordination system would have a survival advantage this gut brain may have actually been the first type of brain to evolve not the second some evidence in support of this view is that the cnidarians the taxa that includes jellyfish and which are some of the evolutionarily oldest animal species on the planet have no head brain but instead a nerve net that looks a lot like our nervous system in our guts this simple nervous system allows them to move and coordinate a simple form of digestion which is basically just contracting the muscles that allow food into their simple bodies taylor guthrie a neuroscience phd student at the university of oregon argues that the nervous system evolved as a kind of cellular republic which is also the name of his youtube channel as he explains in this clip of an interview he did with me over the course of our evolution not just as humans but organisms in general i think that the nervous system itself is kind of this biological government in a way as species evolved it kind of followed in a way this kind of like maslow's hierarchy of the brain first needed to accomplish physiological needs it needed to make sure that all of these different communities of cells all had what they need to survive right homeostasis was maintained and that food was coming in and water was coming in and then and then from there there was this need to be able to protect itself to achieve these kind of safety needs that the organisms had in general and so you see these these brain mechanisms start to come online and when you look at kind of the the older regions of the brain they tend to be more involved in physiological structures or physiological type stuff and then you start to see things like the locus aurelius and midbrain and these other regions that are really involved in like orienting type actions for for like looking for danger and things like that once brains evolved and had been around for a while evidence indicates that humans descended from an ancestor similar to chimpanzees which descended from other animals namely mammals which descended from reptiles which descended from fish with this sketch of our history we can look at the brains of some major groups of animals fish reptiles and mammals and humans and see how they compare this image from a 2016 paper by dennis and oleg guffrov shows a brain from each of these types of animals the hand-written numbers indicate the following brain structures one cerebral cortex two cerebellum three brainstorm four rhine encephalon now the biggest thing to notice is that by volume the fish brain is mostly brain stem and the human brain is mostly cerebral cortex as a very rough approximation we can take the lead of the neuroscientist jeff hawkins and divide the brain into two functional units the cortex or more specifically a division called the neocortex or new brain which allows for complex thought perception and action comprises the vast majority of the human cerebral cortex and these subcortical brain regions including the brain stem or old brain which allow for bodily regulation the execution of movements and the production of raw emotions and feelings the neocortex has a special cellular architecture that allows it to be highly flexible in what it does it's like a quilt with a pattern made by repeating the same unit spaced equidistant in all directions the unit is known as the cortical column it's composed of about 100 neurons arranged into a column that spans the distance from the top of the neocortex to its underside hawkins argues that each cortical column models a small aspect of the external or internal world and that the whole quilt essentially models reality as it is known to the individual person hawkins believes that this is the neurological origin of intelligence and that a given species average intelligence is determined largely by the number of cortical columns in the neocortex thus as you move from the fish brain to the human brain the neocortex explodes in size and likely with it the intelligence of the organism our cortex is so big that it needs to be folded and crumpled to fit into the skull especially highly developed in the humans is the prefrontal cortex or pfc which is the area right at the front of the cortex that's significant because it's primarily the pfc that allows us to inhibit or alter our basic impulses such as for food sex and other forms of instant gratification in general the pfc and its associated networks allow us to engage in cognitive control which as defined by neuroscientist david better it's a function of first actually a bunch of different mechanisms that the brain has to take our goals take our plans uh our intentions and translate them into actions it sort of bridges this gap between knowledge and action so why did cognitive control also known as executive function evolve in the first place there are a couple things to say about this i guess one is is i i think is a question of what is it that cognitive control is doing functionally what is it that it does right and i think one of the key aspects that control offers us is this is generative behavior and flexible behavior the ability to do tasks we've never done before based on an abstract concept of what that is we have to there has to be a way to do that that's because the way we that means we have to be able to structure our tasks in ways that are compositional that means we can break them down into into pieces and then we can reassemble those pieces into new tasks as we need to and that we need a way of doing that um being it being able to generalize that right so then you'd be able to specify something or we can re we can um reassemble it and um that and that's something that for instance i think is unique about human cognition that's one thing we need and but the second component that i think is important is our ability to engage in episodic future thought that we can we can also conceive of futures that we've never experienced before we can we can understand you know through language as well right we can understand what um what we need to do and we can imagine these tasks and then we can structure here so those two things together are are the critical um functions other mammals and especially our closest living cousins the great apes the chimps bonibos gorillas and orangutans have pfcs but they're less cellularly complex in the case of the great apes and in the case of other mammals they're also comparatively smaller thus it appears that our new brain our neocortex accounts for much of what makes us human keep in mind though that all brain regions changed over the roughly 370 million years from when our fish ancestors evolved into land dwelling creatures and eventually into modern humans also the dividing line between the new and old brain is blurry that is there are regions that don't fit neatly into one category or the other including the hippocampus which allows for memories of people places and things and events but it is also involved in emotion and the cerebellum which coordinates smooth movements but is also thought to be involved in many higher cognitions as well as the computational neuroscientist mark humphries pointed out in an interview with me but there's a whole classic series of studies from the from the 80s and early 90s where for me in washington where they uh aspirated so vacuumed off yeah the cortex entirely from the outside of various rats brains and observed them for months on end and all they could note that they weren't very good at was social interactions because they no longer had a prefrontal cortex to suppress some other more sort of basic urges um and uh they couldn't trim their toenails there's a tendency to obscene to view then cortex as this seat of all the higher functions and the rest of the brain is doing some kind of plumbing work right yeah difficult stuff but really there is no there is no sort of separation yet sure in humans the cortex is is quite elaborated but so is so a huge chunks the rest of the brain it's really best to think of the brain as a whole when a break as a holistic thing um and there isn't and there's yes so this misconception this is kind of cortex that separates from the rest it's a strong one particularly people who still cling to this idea that uh simpler animals don't have cortex so there's kind of like a three level brain thing there's a like a brain like a reptilian brainstem thing and then it's like a simple mammal midbrain thing and then there's a like advanced creature cortex thing there is no vertebra that doesn't have something that looks like cortex even the lamprey which is like a tube of teeth basically um which diverts from us about 350 million years ago it has a little tiny neural crest thing sitting on top of its midbrain which has got you know few cortex-like cells it's not layers but it's a thing that's there it's best really best to think about offer not the cortex of some kind of seat of highest higher function but it obviously integrates with the rest of the brain to produce whatever it produces evolutionary influences on the brain's form are intriguing but we are ultimately interested in how the brain works its function and this too has been deeply influenced by natural selection in other words evolution shaped human psychology just as it did for our neurology an example is in the realm of sex and the differences between men and women the most fundamental of these may be the fact that on average men are more likely to want more sexual partners and women fewer throughout their life that makes sense if you think about the evolution of our species not as the survival of the fittest but as the tendency of genes to make more copies of themselves so they can make it into the next generation if you're a gene trying to get yourself copied as many times as possible your strategy for doing so will be different in the body of a male compared to a female now why is that well for a man to reproduce all he has to do is fertilize a female's egg and there is no limit to how many eggs can be fertilized that is a man can have an unlimited number of offspring thus in evolutionary terms and all else being equal it is in the best interest of the man's genes to influence that man to have many sexual partners throughout life that will give his genes the best chances of being copied many times continuing into the next generation and repeating the cycle for women the only way to reproduce is to fertilize one egg at a time nurture it to develop into a baby birth that baby and take care of it for years until it can live on its own there's a lot of room for disastrous errors in that long sequence of events including death from malnutrition at all developmental stages therefore a woman is more likely to be concerned with ensuring that her precious few offspring are well fed and taken care of that provides her genes the best chances of being copied into the next generation okay this discussion can get controversial so let's just issue a few caveats as you can probably tell the idea that men want more sexual partners and women fewer is not an ironclad rule that is always true similarly the evolutionary strategies are not quite as simple as i've made them out to be for example it is also in the man's genes interest to ensure that his offspring survive and reproduce so simply abandoning his pregnant partner to go find another is not always going to be optimal finally when i say it's in the best interest of the genes i do not mean that this is therefore somehow morally justified nor that it is in the best interest of the individual person so our sexual behaviors can be partly explained by our evolutionary history what else does evolution influence mental illness may not just be miswired neural circuitry but perhaps also an unfortunate result of evolutionary adaptations as the science writer brett stetka writes in his 2021 book a history of the human brain quote some psychiatric conditions might be pathologic exaggerations of beneficial traits a little anxiety has clear evolutionary advantages but a little too much is crippling end quote the advantages he speaks of are that you're more alert more concerned about what could go wrong in the future and therefore more likely to avoid bad outcomes but if you inherit too many genes that predispose you to anxiety it may be difficult for your brain to cope with stress in a healthy way each of the symptoms that contribute to major depression like low mood withdrawal from social life and others may have as argued by researchers paul andrews and zachary duresco in a chapter of the oxford handbook of mood disorders they may have evolved for general purposes of coordinating quote the re-allocation of limited energy resources in response to persistent threats end quo these are interesting ideas about how the deep past affects our brains today however the evolution of the human brain and the psychological consequences are still not yet fully understood so this video is barely a sketch of our evolutionary history of our species and it's certainly not a comprehensive account instead it's meant to give you an idea of where our brains came from in a coarse grain view of the history of life so thank you so much for watching this video please make sure to like and subscribe and let me know what you think in the comments also please consider signing up for sense of mind's weekly video newsletter which you can find at senseofmindshow.com as always this channel is brought to you by the diamond mind foundation this video was written and produced by me andrew cooper sansone thank you so much for watching i'll catch you next time [Music] you