I just want to take a minute to point out another interesting property of beavers and their dams, ecological inheritance. Baby beavers inherit their various physical and behavioral adaptations from their parents through their genes. But they also inherit their environment, the lodge and dam their parents have built, and the flooded land behind it. Some beaver dams are absolutely massive and they can last for decades, way more than the life of an individual beaver. This, therefore, constitutes a type of nongenetic inheritance sometimes called ecological inheritance. As well as giving you their genes, your parents can pass on other stuff to you. If you're a beaver, this includes a dam. Ecological inheritance is rife in humans, of course. Think of all the aspects of your environment that your parents shaped for you, starting with the house that you grew up in. But we also inherit knowledge and behaviors directly from our parents and other people, not via our genes but via social learning. The ability to learn, to modify your behavior in response to your environment is very widespread in nature. Basically, every organism can do this. Social learning, is learning from the behavior of others, is also pretty common. So apes and other primates do it, but other mammals do it too like rats and birds do it, and even some fish do it. But humans are definitely the premier social learners. Think of all the things you know and the skills you have that you were taught by another person, or you copied from someone else, or, that you read in a book, or saw in a video on YouTube. On top of ecological inheritance, social learning forms an important non-genetic mechanism for the transmission of knowledge and behaviors in human populations, and I think understanding social learning is crucial to understanding human evolution. Humans have large repertoires of behaviors which are transmitted by social learning, and the collective term for these is culture. So, culture informally, is often used to refer to highbrow activities like going to the ballet or attending a piano recital. But its technical usage just refers to any system of knowledge and behavior which is transmitted by teaching, imitation, or other forms of social learning. So culture in humans includes things like the clothes you wear, the kind of house you live in, the food you eat, and the language you speak. And other animals have culture too, because they do social learning. So for instance different chimpanzee populations have different repertoires of behavior. So you find that some chimpanzee populations crack nuts using a simple hammer and anvil, and other chimpanzee populations, which are otherwise very similar, don't. And this is a cultural difference, rather than, for instance, a genetic difference. Animal cultures are very simple. It look as if a single individual invents a new behaviour and then it spreads through the population as that animal is copied by others. So the reason that some chimpanzee populations use a hammer and anvil to crack nuts and others don't is just because in the populations where nobody does it, no individual has discovered that behaviour yet. Since different innovations occur in different populations, over time separate populations accumulate their own idiosyncratic inventory of these certain behaviors. Human culture doesn't work like this. Rather than being a collection of simple behaviors and artifacts, human cultures and the products of human culture are enormously complex. So think of how complex a bicycle is, or a car, or a computer, or even your clothes with all the different fabrics and fasteners, or think of how complex the political and legal institutions are in your country and how they got to be that way. These complex objects and behaviors weren't invented by a single individual who everyone else copied. Rather, it represents the gradual accumulation of modifications over hundreds or thousands of years. You inherit a behavior and then you modify it and improve its design. And then you pass on that modified version. And this process where one generation builds on knowledge inherited from previous generations is called cumulative culture. And the objects it produces are enormously complex and well-designed. So at least some interesting human behaviors and artifacts are parts of cumulative culture rather than being biological adaptations. Remember the beavers and their dams. An instinctive behavior carried out by the beavers which changed their environment, increasing some selective pressures and reducing others. Humans do exactly the same kind of sculpting and shaping of their environment on a massive scale. Unlike beavers, the things we do to shape our environment, things like wearing clothes, building shelters, growing crops and keeping animal for food. Living in large complex social groups, are not instinctive behaviors but socially learned. They're part of culture and you learn how to do these things from the people around you. Nonetheless, just like beavers and their dams, all these modifications we make to our environment massively change the selective pressures acting on us. Our ability to insulate ourselves from hostile environments with clothing and housing has allowed us to spread right across the planet and inhabit hostile environments, like the high plains of the Andes, or the Arctic Circle, which would otherwise be uninhabitable. As well as insulating us from some selection pressures, our cultural practices have set up new selection pressures acting on human populations. One of the most famous examples is the evolution of lactase persistence. So most mammals lose the ability to process lactose, that's the main carbohydrate in milk. After weaning, there's essentially no need to carry on producing lactase, That's the enzyme that the body uses to break down lactose, after you stop drinking your mother's milk. But in a minority of the world's human population, adults exhibit what's known as lactase persistence. They carry on producing lactase after the point of weaning, and this enables them to break down lactose, and therefore, benefit from drinking animal milk. This is a very handy ability to have cause milk's a great food source. It's rich in protein and fat. Around a third of the world's adult population exhibit lactase persistence, mainly in northern Europe and North Africa. And the rest of the human population don't exhibit lactase persistence. They're just like normal mammals, losing the ability to process lactose after weaning. So why do some of the world's population exhibit lactase persistence? It's clearly a genetic trait, and what's more, it's probably an adaptation, since it's such a handy ability to have. It's thought that lactase persistence evolved really recently, in the last 10,000 years, in response to the cultural practice of dairying, keeping animals, and drinking their milk. Lactase persistence is really common in populations with a long history of dairying, and it's scarce in populations with no dairying tradition. So the idea is that the cultural practice of dairying set up new selection pressures acting on dairying populations, rewarding individuals who were able to drink milk for longer in life and reap the rewards of milk drinking. The genes of these dairying populations responded to this new selection pressure. and evolved this capacity for lactase persistence. And this biological adaptation probably fed back into the cultural practice, further promoting the exploitation of dairy products and setting off a mutually reinforcing spiral of gene culture coevolution. Lactase persistence is probably the most famous case of human genes responding to selection pressures set up by human culture. But it's almost certainly not the only one. Recent estimates based on sophisticated techniques for identifying the hallmarks of selection in human genetic databases suggest that thousands of genes have been under recent selection in the past 40,000 years. Probably as a result of selection pressures set up by human cultural practices. So you might think that the human capacity to insulate ourselves from our environment means that natural selection is effectively over for humans or you might agree with the evolutionary psychologists that we have stone age minds and modern skulls. But in fact, this research suggests that the rate of human evolution has actually increased in the last 40,000 years, as our genes respond to the new environments we create for ourselves via culture. So I spent a little bit of time applying these ideas to a problem that I work on, the evolution of language. The human language is a uniquely powerful, flexible communication system that has no parallel in the natural world. Basically every species communicates. Flowers signal the availability of nectar to bees, and bees communicate with other bees about the location of flower patches. And male birds sing for female birds to advertise their availability and quality. And lots and lots of species have alarm calling systems. They have specific calls that communicate to group members about the presence of specific predators. These are all fascinating communication systems. But compared to human language, they're incredibly rigid and inflexible. An alarm calling monkey can't use its alarm calling system to reminisce about a predator they saw yesterday or to plan what they should do next time they see a predator. In contrast, human language is incredibly flexible and powerful. Basically, anything I can think, I can communicate to you using language. Provided you'll be able to figure out my accent. Language has a bunch of structural devices which enable it to achieve this open ended expressive power. At the most fundamental level, the expressive power of language comes from the fact that it has rules. Speakers of a language know the meaning of a bunch of words and they importantly know the rules of that language that govern how those words are combined. And this means that as long as you know the meanings of the words and the rules of the language, then you can understand any sentence that follows those rules. So all the things that Suilin and I have said in this lecture today have been completely novel and one off sentences of English that have never been spoken before and will never be spoken again. And nonetheless, because you implicitly know the rules of English, you've been able to understand what we mean. Within this basic framework, language provides devices for conveying all kinds of useful information. You can encode who did what to who. In a language like English, you convey this information using the order of words in a sentence. In a language like Hungarian, you do the same job by attaching markers to the ends of words. This allows you to distinguish between, for example, the news that the dog chased the cat or the cat chased the dog. You can see when an event happened in time, allowing you to convey whether something already happened, or will happen in the future, or is happening right now. You can convey that an event might happen, or will happen, or might not happen, or won't happen, and you can explain why. You can ask questions that require a simple yes/no answers or request more complex information. How have humans ended up with such a fantastically rich, complex communication system? One possibility is that language and all these grammatical devices for communicating complex information are an adaptation. This argument was made by Stephen Pinker and Paul Bloom in a well-known 1990 article called Natural Language and Natural Selection. In their paper, they argued that language is a complex biological trait that appears to be designed for communication. The only way to explain such traits it to appeal to natural selection. Humans live in complex social groups. As Suilin already said, this means we spend lots of time thinking about social events, like who is cheating on who. But it also means we rely heavily on communicating with other people. Sometimes we want to exchange information about current social events or immediate survival relevant situations. But we also want to pass on the complex set of knowledge, skills, and beliefs that are needed to survive in the world. Language is obviously well-designed for doing all these things. And therefore, so the argument goes, the ability to learn a language must be an adaptation. So, it could be that the complexity and communicative power of language are the product of an evolved language instinct. A mini-computer, or a series of mini-computers that have specialized for language learning and language processing. And, there's clearly something uniquely human involved in language. No other species has a communication system that works like language. And attempts to teach human language to non-human animals have met with only limited success. But in my work, I explore an alternative possibility, the idea that some of the interesting structural properties of language are a product of culture rather than biology. And in particular, I explore the idea that these interesting features of human language are a product of cumulative culture, the gradual accumulation of modifications that I talked about earlier on. So we know for a fact that languages are socially learned. The reason I sound the way I do is that I grew up around a whole group of people who sound like this. And I learned my particular version of English from listening to the way those people talked, and they in turn learned their language in the same way. So your parents were influenced linguistically by their parents and peers who were in turn influenced by their parents and peers, and so on. In a process of transmission that stretches back tens of thousands or maybe even hundreds of thousands of years. And we also know that language has changed as a result of this transmission process because we can see it in the written record. So, the English of today is very different from the English spoken in Shakespeare's time. And the English spoken 1,000 years ago would be incomprehensible to a modern speaker of English, because the language has changed so much. Our historical record for languages doesn't actually stretch back very far. Writing was only invented 5,000 years ago. And as far as we can tell, the first languages to be written down work in basically the same way as modern languages in having rules and structure of the sort that I mentioned before. But languages must have been around a lot longer than 5000 years. They must have been around as long as there were humans on the planet, and maybe even longer. So, that means that languages have a fantastically long period of time to evolve by cumulative culture. And it could be that the complexity and communicative power of language arose as a result of cumulative cultural evolution over this timeframe. In order to survive, languages have to be highly learnable. They have to make it into the minds of language learners. Language learners simplify, and regularize, and generally tidy up languages as they learn them. As a result, languages evolve to have rules and patterns and regularities, that language learners can identify and exploit, because those patterns make language more learnable. At the same time, people consciously or unconsciously modify the way they use their language in order to make the distinctions they care about and meet their communicative needs. So for instance, you might choose the most concise or clear or funny or inventive or colloquial way you can think of to express yourself. So people modify their language to meet their communicative needs, in much the same way they modify tools and other cultural products to improve their function. The only difference might be that the modifications we make to language are more subtle and perhaps less intentional. But over hundreds of thousands of years, these changes in conjunction with the simplifying and systematizing consequences of language learning might conspire to produce complex, expressive, rule governed languages. This is just a hypothesis of course. But I think its a good one. And its one we can test. We can't study the early origins of language directly, but we can study how languages are learned in the present and how they change over historical time. And we can simulate these same processes of learning and change either in a computer or using real people in the experiment lab. If this theory is correct, it means that some of the most important structural features of language which makes language such a wonderfully powerful and expressive communication system, may be a product of culture rather than a biological adaptation. >> We started with the premise that our brains are a product of natural selection. We then looked at two different ways that we could develop this claim. The first, evolutionary psychology says that our brains evolved during the environment of evolutionary adaptation about 2.4 million years ago. The brains that we have today are a series of mini computers, each of which involve to solve a specific problem that faced our ancestors during the environment of evolutionary adaptation. >> The second account suggests that the human brain's undergone significant evolution in the last 10,000 years, as a result of our capacity for a cumulative culture which has enabled us to shape our environment to better suit our needs. Culturally transmitted niche construction behavior like dairy farming have set up new selection pressures and have driven rapid evolution in our genes. Evolution psychology paints a relatively passive view of evolution, with an organism responding to challenges imposed by the environment. Niche constructing accounts emphasize how organisms alter their environments, set up new selective pressures. This is of course a caricature of the two positions, but it highlights one of the key differences between them. Humans are unique in our capacity for high fidelity social learning, the sheer amount of social learning we do, and the cumulative culture that this produces. Language clearly plays a pivotal role in setting up these systems of social learning. But again, we see differences in the two accounts in how they explain the evolution of language. Evolution psychologists will look for a series of language modules in the brain, specialized mini computers which enable us to learn and process language. Researchers persuaded by the cultural account will instead focus on how languages change and evolve in order to be easier to learn and more expressive to use. >> We've only been able to give a short overview of the two main position in this MOOC. But if you're interested, we've put some further reading on the handout for you to look at. Researchers are really interested in the interaction between evolution and culture and it remains one of the fiercest and most stimulating debates in cognitive science at present. The mind may not be a blank slate but we still have a long way to go before we fully understand the nature of knowledge that it contains.