The history of the world is the memory of the past experience of Homo sapiens sapiens around the world, as that experience has been preserved, largely in written records. By "prehistory", historians mean the recovery of knowledge of the past in an area where no written records exist, or where the writing of a culture is not understood. By studying painting, drawings, carvings, and other artifacts, some information can be recovered even in the absence of a written record. Since the 20th century, the study of prehistory is considered essential to avoid history's implicit exclusion of certain civilizations, such as those of Sub-Saharan Africa and pre-Columbian America. Historians in the West have been criticized for focusing disproportionately on the Western world.[20] In 1961, British historian E. H. Carr wrote: