The similarity between intelligence scores of fraternal twins reared together is:

Video transcript

- [Lecturer] You've probably heard of IQ, which means intelligence quotient, and you may even have taken an intelligence test, which is supposed to measure how intelligent you are, but what does intelligence mean? For a term that's used so widely we have kind of a hard time defining it. Does it mean street smarts, book smarts, creativity? Psychologists, even though they still have some disagreements, tend to define intelligence as a mental quality, allowing you to learn from experience, solve problems and use your knowledge to adapt to new situations. Intelligence tests use numerical scores to measure your aptitude for those types of tasks and compare them to how well other people do. So if intelligence is made up of different aptitudes, then is it multiple abilities or is it just one? One theory is that there's just one general intelligence. Evidence to support this theory comes from the fact that people who score really well on one type of test, such as verbal ability, also tend to score really well in other types of tests, such as math. Now, you might be better at one of these categories than the other, relative to yourself, but relative to other people you probably have about the same level of skills in both areas. The factor underlying these consistent abilities is referred to as the g factor. You can think of g for general intelligence. Although there's some good evidence for g, there's also some support for theories of multiple intelligences. A psychologist named Robert Sternberg proposed a theory of three main types of intelligence, analytical intelligence, what we might think of as academic abilities or the ability to solve well-defined problems, creative intelligence, the ability to react adaptively to new situations and to generate novel ideas, and practical intelligence, the ability to solve ill-defined problems, such as how to get that bookcase up the curvy staircase into your apartment. When someone tells you their IQ score what they're really telling you is their analytical intelligence. The scores are scaled so that an average person scores 100, so depending on where you are in relation to 100 you can tell how you compare to the population at large. You may be wondering how intelligence affects people's lives. Obviously, people with high analytical intelligence tend to do well in school, however, people who score high on any of the intelligence scales we've mentioned so far don't really tend to have better marriages, raise their kids better or achieve greater mental and physical well-being than people who score lower. For this reason, another psychologist proposed that there is another type of intelligence called emotional intelligence. This ability helps you perceive, understand, manage and use emotions in your interactions with others. Yet another way of thinking about intelligence is in terms of two major categories, fluid intelligence and crystallized intelligence. Fluid intelligence is our ability to reason quickly and abstractly, such as when we're solving novel logic problems. Crystallized intelligence, on the other hand, refers to our accumulated knowledge and verbal skills. The main difference here is that fluid intelligence tends to decrease as we move into older adulthood, whereas crystallized intelligence tends to increase or stay the same. With all this talk about different definitions of intelligence, you're probably wondering how it ever gets measured. Interestingly, the first person to develop an intelligence test actually didn't even mean for it to be an intelligence test, Alfred Binet was just trying to establish a child's mental age in order to measure children's intellectual development and predict how well they would do in school. Later on, a psychologist at Stanford University modified Binet's original test and extended it to teenagers and adults. One thing that the Stanford psychologist noticed was that Binet's original test items, which were originally designed for French children, didn't seem very predictive of California children's abilities. After he modified the test, unfortunately people forgot about that difference and started using the new version to judge how generally intelligent immigrants coming into the US were. Now, you can probably see the problem with that, even from just a language perspective. If a test is trying to measure verbal ability, then you might be able to do just fine in your native language, but it's a lot harder in a language you don't know. Since then, more pains have been taken to try to make intelligence tests more applicable to people from all different cultures, but it's an ongoing issue. One last consideration that's inherent in any question of traits or talents, but particularly popular with intelligence, is the question of nature versus nurture, that is, how much is intelligence due to your genes and how much is due to your environment and other experience? We study this question by looking at heritability, which is the proportion of variability in a trait that's due to genes. Specifically, we usually study heritability with twin and adoption studies, meaning we look at the corelation between intelligence scores in identical twins, two people with the exact same genes, who grew up in different environments. We also look at the corelation and scores between identical twins raised together, as well as the corelation and scores between fraternal twins raised together. Since we have a mix of same and different genes and environment, we compare those correlations and try to determine what proportion of the variability in those scores we can attribute to genes and what proportion is attributable to the environment. What we know from these studies is that of those three groups there's the strongest corelation and IQ scores between identical twins raised together. That alone doesn't really tell us about any differences between nature and nurture, though, so let's keep going. Identical twins raised apart still have a high corelation, but not as high, suggesting some environmental influence on intelligence. Fraternal twins raised together have an even lower corelation, though, suggesting that there is also a genetic component. So the short answer is both nature and nurture contribute to intelligence. Since we tend to have more control over the nurture aspect than the nature aspect, there's been a lot of research into what types of environments promote intelligence, especially for children. Interestingly, although we know some environmental situations that impair normal cognitive functioning, there's no recipe for structuring an environment to make a genius, when children are deprived of exposure to language or interaction with people, their intellectual development is impaired. However, there's not a direct relationship, tons and tons of language exposure helps a child, compared to no exposure, but it doesn't necessarily make that child a genius. Perhaps even more important than just intelligence score is your attitude toward intelligence. Some people have what's called a fixed mindset, they think that intelligence is biologically set and unchanging, others have what's called a growth mindset, meaning that they think intelligence is changeable if you learn more. People with a growth mindset tend to be more motivated and able to accomplish more in their careers, than people with a fixed mindset. So, whatever your IQ score is or isn't, try to keep in mind that you can always grow and always learn.

Who are likely to show the greatest similarity and strongest correlation in IQ scores?

Which of these items on an intelligence test would be most likely to be considered culturally biased?

Which statement best describes how a scientist would describe a biased intelligence test?

Which statement is the best summary of the research findings about the impact of stereotype threat?