ABSTRACT
How did humans appear upon the Earth? For that matter, how did any living thing get here? For most of the Earth’s 4.5-billion-years history, nothing larger than one-celled animals existed. In the last 500 million years, multi-celled animals came into being and left fossils behind. The animals existing today have descended from those early ancestors. In this chapter, we will discuss how science has unraveled that story.
