Over the past decade or two, there have been some intriguing changes in the attributes of the teenager. The psychologist Jean Twenge of San Diego State University notes that teens are growing up more slowly by many measures, compared with their 20th-Century counterparts. A typical 17-18-year-old in the US, for example, is now less likely have tried alcohol, have had sex, or acquired their driver"s licence, compared with similarly-aged teens only 20 years ago. A 13-14-year-old is less likely to have a job or to have gone on dates. Meanwhile other measures of early adulthood, such as teenage pregnancy, have reached historic lows in the US and Europe.