The Earth has a population of 7.8 billion, with an overall population density of 50 people per km2 (129.28 per sq. mile), excluding Antarctica. Nearly two-thirds of the world's population lives in Asia, with more than 2.7 billion in the countries of China and India combined.[1][2] The world's literacy rate has increased dramatically in the last 40 years, from 66.7% in 1979 to 86.3% today.[3] Lower literacy levels are mostly attributable to poverty. Lower literacy rates are mostly found in South Asia and Sub-Saharan Africa.[4] The world's largest ethnic group is Han Chinese, with Mandarin being the world's most spoken language in terms of native speakers.