Prehistory is a term that refers to events that occurred before the development of writing. This period is divided into the Paleolithic, Mesolithic, and Neolithic time periods. During the Paleolithic time, humans developed the use of simple tools and evolved as a species. The Homo erectus evolved into the Homo sapiens sapiens, of which all humans are descendants. With the Homo erectus came speech, the development of language, and the spread of the people throughout the world. In the Mesolithic time period 12,000 to 8000 B.C.E., people started to domesticate animals and the population grew, which lead to many conflicts and wars. The final stage of Prehistory is the Neolithic. During the Neolithic time period people began to develop agriculture and cities, which lead to civilizations that had written languages. This was the end of prehistory. While there are other records that historians use, such as art and artifacts, to understand and gain knowledge about history, writing remains the most reliable and productive record.