A world map showing the continent of Africa. (See Politics section for a clickable map of individual countries.) Africa is the world's second-largest and second most-populous continent, after Asia. At about 30,221,532 km² (11,668,545 sq mi) including adjacent islands, it covers 6% of the Earth's total surface area, and 20.4% of the total land area.[1] With more than 900,000,000 people (as of 2005)[2] in 61 territories, it accounts for about 14% of the world's human population. The continent is surrounded by the Mediterranean Sea to the north, the Suez Canal and the Red Sea to the northeast, the Indian Ocean to the southeast, and the Atlantic Ocean to the west. There are 46 countries including Madagascar, and 53 including all the island groups. Africa, particularly central eastern Africa, is widely regarded within the scientific community to be the origin of humans and the Hominidae tree, as evidenced by the discovery of the earliest hominids, as well as later ones that have been dated to around 7 million years ago – including Sahelanthropus tchadensis, Australopithecus africanus and Homo erectus – with the earliest humans being dated to ca. 200,000 years ago, according to this view. Africa straddles the equator and encompasses numerous climate areas; it is the only continent to stretch from the northern temperate to southern temperate zones. Because of the lack of natural regular precipitation and irrigation as well as glaciers or mountain aquifer systems, there is no natural moderating effect on the climate except near the coasts.