Over the past century, the average IQ in industrialised countries has risen to keep pace with the complexity of modern life. IQ researcher James Flynn notes down three main things that have caused these changes.
1. Formal schooling which contributed to the huge gains in vocabulary and general information available to modern people. People today on average know enough vocabulary to mimic the speech of only the cultural elite of 1900.
2. Scientific habits of mind. If you asked a question "What do dogs and rabbits have in common?" In 1900, a person would say, "You use dogs to hunt rabbits." Today you say, "They're both mammals." In the past, people's minds were utilitarian. They weren't interested in hypotheticals or in classifying things together. But today people have scientific habits of mind.
3. Wealth of visual images in the modern world. This might be responsible for improvements in mapping skills and in looking at three-dimensional figures and how they rotate.
This doesn't mean that modern people have better genetically engineered brains. But it does mean that we've gained in intelligence. The average person can do creative work today that they couldn't do in 1900. Also, people today are mentally adapted to a far more complicated world.
Source: American Psychological Association, March 2013. Read the full article.