So far in this course, we've discussed universals what people have in common. So, we've talked about capacities like language, memory, learning, and their emotions. But, people differ from one another, and actually in our everyday lives it's the differences that matter. If I want to describe a friend of mine I wouldn't say, "Oh, she has a short-term memory and long-term memory." If I wanted to introduce you to somebody I wouldn't say, "Oh, he has emotions that have evolved through natural selection." We're really interested in our everyday life in how people differ is the differences that matter. So, there's a couple of questions we can ask as psychologist, one of which is the nature of the differences, how are different? And then the second is the explanation for the differences, why we're different? There are all sorts of differences as psychologists might look at. Some of us see ourselves as male, others as female, others in ways that don't cleanly map onto either of the two. Some people are attracted sexually, romantically to males, some to females, some to both, some to neither. Within these categories there's a lot of subcategories, sometimes you're sexually or romantically attracted to one type of person or another. It's really interesting to ask why is this so? What shapes your preferences? What's the nature of these preferences.? Some of you are happy, others are less happy. Obviously, it varies according to your circumstance, but also people are in general either they vary in the extent to which you're happy or unhappy, and this is so interesting that the very last lecture, we'll discuss this. Some people have good relationships, and good jobs, and good dealings with their community, and others don't. Some people become alcoholics and drug addicts, others don't. When this gets extreme, we call it psychopathology mental illness. But moving outside the range of mental illness, there's just a lot of variation in people. Now, we'll focus today on two dimensions that are actually related to life success, personality and intelligence. We'll first talk about what these differences are, how people differ, and then we'll turn to the question of why.