Humans share ideas because they have language. But language also allows us to talk to ourselves. That is, it allows us to think in ways that are not possible for other animals. So humans are thinking as well as talking animals. Words allow humans to think not just about the things that are right in front of us. They also allow us to think about abstract things. We can think about “the universe,” “the gods,” or “democracy.” We can ask abstract questions such as, “What is a human being?” (We have no evidence that cats ever ask themselves, “What is a cat?!”) And of course what we think affects what we do. If we believe in cooperation and sharing, we will give our time and money to help others. If we believe it is our duty to sacrifice ourselves in war, we may do that. So it really matters what ideas people have in their heads.

Some of the most powerful ideas in human history have been about techniques for living. New technological ideas from the invention of the wheel to the nuclear bomb can transform how millions of people live. Indeed, the way technological ideas have accumulated over time and the effects they have had on society is one of the main themes of world history.

Equally potent are ideas about social organization, government, the environment, morality, and spirituality. People will go to great lengths to obey the god in whom they believe. Similarly, they can take offense if others behave in ways they regard as immoral and insulting, even if those others have no sense that what they are doing is in any way unacceptable. Walking around naked in public may be no problem in some societies but intolerable in others. Complex belief systems, including religions, philosophies, and political ideologies such as Marxism, have had a profound impact on human behavior, particularly in the last few thousand years. Humans, for example, have always wrestled with ideas and beliefs regarding political authority: Who has the right to rule? When is rebellion against government justified?

According to recent research, humans may have begun at least 90,000 years ago to express ideas symbolically by painting their bodies or carving decorative marks in bone. By 10,000 years ago, humans expressed themselves and communicated with one another in sophisticated ways through painting, sculpture, music, and the decorative arts. In more recent millennia humans invented writing systems that gave birth to many forms of literature. We can learn much about the past by exploring aesthetic, that is, artistic and literary expression.

The very stories we tell about the past, from popular myths and legends to scholarly historical studies and textbooks, reveal humankind's amazing capacity to think about itself-where it has been and where it is going. In exploring ideas in history, we should keep in mind that humans continue to construct, reconstruct, and dispute the past. This curriculum itself is the product of much reflection, discussion, and argument. World History for Us All invites teachers and students to explore ideas in history critically, even the ideas on which this curriculum is based!