In this lesson, small collaborative groups of students will watch one of five video time clips from the What Are We? episode to draw conclusions about evolution and determine how humans came to be. Living organisms on Earth today, and the chemicals which work together to keep them alive, are extremely complex. Some find it difficult to accept that such complexity could have evolved through natural selection. We will probably never be absolutely certain about how life began, as no one was there to observe it. But scientists, and students, must base their theories on evidence.