Africa is the world's second-largest and second-most populous continent. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area and 20% of its land area, accounting for about a fifth of the world's land. With 1.3 billion people as of 2018, it accounts for about 16% of the world's human population. It is surrounded by large areas of water. There are 54 fully recognized and independent countries in Africa, and 14.7% (1.216 billion) of the world's population lives there. It is thought to be the continent where the first humans evolved.