Evolution and human culture

- [Voiceover] When sociologists talk about culture, they are referring to customs, knowledge, and behaviors that are learned and socially transmitted. It includes the ideas, values and even objects that are meaningful to a group of people. And because culture is typically learned through observation and interactions with those around us, it might surprise you that there is actually a biological component to culture as well, and that it has actually been shaped through evolution. Remember that the Theory of Evolution was put forth by Charles Darwin, and he noticed that small variations in species, we'll use the beaks of finches as an example, he noticed that they varied over different locations. So these finches would have short beaks on one island and long beaks on another. And he theorized that this occurred because of interactions between the organisms and their environments. That the animals who are best suited for living in certain environments would have the greatest likelihood of both surviving in that environment as well as passing on their genes. So let's imagine that we have an island full of finches, and let's say that because of a drought the only plants that now thrive are ones that happen to have seeds at the bottom of flowers with very long petals. And there's natural variation in beak size within our finch population, exactly how there's a natural variation in height in the human population. And before the drought, that didn't matter at all because seeds were available on all types of flowers so it didn't really matter what kind of beak you had, you could always get them. But because this type of flower happened to thrive after the drought, now suddenly the birds with long, thin beaks are much better adapted to their environment than the birds with thick, short beaks. And because our long-beaked birds are the ones that can reach the seeds and eat, they are more likely to survive and, importantly, they're able to survive to an age where they can reproduce. And so over time, if these same environmental conditions continue, the population will eventually trend towards long, thin-beaked birds. And what Darwin realized was that if the environment could select for small, individual traits, then slowly, over hundreds and thousands of generations, nature could shape an entire species. And as always, when we're talking about evolution, we're talking about the whole population, not about individuals or even smaller groups within that population. So let's take this and think about social behavior. So before we said that some kind of physical attribute might be selected for if it helps the animal fit in with its environment. Well here we're talking about the same thing, but we're talking about behavior. So we're saying that certain behaviors can also be selected for if they contribute to the fitness of the species. And at this point you might be saying to yourself, "There are lots of different human behaviors. "How would we know if one is being selected for?" And the answer is to think about this in terms of cultural universals. And these are common practices and beliefs that are shared by all human cultures. Think about this in terms of medicine. Cultures might have very different ways of dealing with illness, but what they have in common is that they all have systems or rituals or actions in place for how to deal with illness within their community. Another example would be partnership ceremonies like marriage and also funeral ceremonies or some ritual associated with death. Or think about language and the ability to communicate with others in your group. The fact that these aspects of culture seem to exist in all human cultures, even if they're expressed very differently, it indicates that they might have been selected for as the human species evolved. So these are examples of how evolution can shape culture, but we can also think about how culture might shape human evolution. So think about the transitions from humans as a hunter-gatherer society to one in which crops are planted and raised and animals are domesticated about 10,000 years ago. Because these groups didn't move around so much, because they stayed in one place, populations began to grow. And because of this, people became more exposed to outbreaks of disease within these populations. And since the only people who survived and reproduced were those who weren't killed off by the diseases, our culture, these communities, have helped to shape our immune systems. Or think about lactose intolerance, or the inability to digest milk product. During the first year of life, most humans get all of their nutrition from milk. But the genes that allow us to digest this milk are typically switched off soon after children are weaned. But it turns out that northern Europeans who are descendants of cattle-rearing cultures that existed in the region about 6,000 years ago, they don't show this effect. Their genes that code for the enzymes that break down lactose in milk, they don't turn off. And so think about what might have happened if there was a particularly hard winter. The individuals who are able to digest milk proteins, the ones who are able to get the extra nutrition, they were more likely to survive and reproduce. And consequently they left more surviving offspring that could also digest milk. So while the rest of us tend to get stomach aches if we have too much dairy, these individuals are able to eat all of the ice cream they want because of how their ancestors' culture directed their evolution.