Chapter Introduction

Intelligence

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  • How Can Intelligence Be Measured?
    • The Intelligence Quotient
    • The Intelligence Test

    • THE REAL WORLD Look Smart

  • What Is Intelligence?
    • A Hierarchy of Abilities
    • The Middle-Level Abilities
  • Where Does Intelligence Come From?
    • Genetic Influences on Intelligence
    • Environmental Influences on Intelligence

    • HOT SCIENCE Dumb and Dumber?

    • Genes and Environments
  • Who Is Most Intelligent?
    • Individual Differences in Intelligence
    • Group Differences in Intelligence
    • Improving Intelligence

    • OTHER VOICES How Science Can Build a Better You

WHEN ANNE MCGARRAH DIED at the age of 57, she had lived more years than she could count. That’s because Anne couldn’t count at all. Like most people with Williams syndrome, she couldn’t add 3 and 7, couldn’t make change for a dollar, and couldn’t distinguish right from left. Her disability was so severe that she was unable to care for herself or hold a full-time job. So what did she do with her time?

I love to read. Biographies, fiction, novels, different articles in newspapers, articles in magazines, just about anything. I just read a book about a young girl–she was born in Scotland–and her family who lived on a farm…. I love listening to music. I like a little bit of Beethoven, but I specifically like Mozart and Chopin and Bach. I like the way they develop their music–it’s very light, it’s very airy, and it’s very cheerful music. I find Beethoven depressing. (Finn, 1991, p. 54]

Although people with Williams syndrome are often unable to tie their own shoes or make their own beds, they typically have gifts for music and language. Williams syndrome is caused by the absence of 20 genes on chromosome 7. No one knows why this tiny genetic glitch so profoundly impairs people’s general cognitive abilities, yet leaves them with a few special talents.

People with Williams syndrome have a distinct “elfin” facial appearance and diminished cognitive abilities, but they often have unusual gifts for music and language.
BONNIE WELLER/PHILADELPHIA INQUIRER/NEWSCOM

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WAS ANNE MCGARRAH INTELLIGENT? IT SEEMS ODD TO SAY that someone is intelligent when she can’t do simple addition. But it seems equally odd to say that someone is unintelligent when she can articulate the difference between baroque counterpoint and 19th-century romanticism. In a world of Albert Einsteins and Homer Simpsons, we’d have no trouble distinguishing the geniuses from the dullards. But ours is a world of people like Anne McGarrah and people like us: people who are sometimes brilliant, often bright, usually competent, and occasionally dimmer than broccoli. Which forces us to ask the hard question: What exactly is intelligence? About 20 years ago, 52 scientific experts came together to answer this very question, and they concluded that intelligence is the ability to direct one’s thinking, adapt to one’s circumstances, and learn from one’s experiences (Gottfredson, 1997). As you will see, that definition captures much of what scientists and laypeople mean when they use that term.

For more than a century, psychologists have been asking four questions about intelligence: How can it be measured? What exactly is it? Where does it come from? Who has it and who doesn’t? As you’ll see, intelligence is a set of abilities that can be measured quite accurately, it is the product of both genes and experience, and it is something that some people and some groups have more of than others.