The world's 7-billionth person will be born Oct. 31 in India, according to a projection by researchers working with data from the United Nations. Medical advances, more effective vaccines, antibiotics and improvements in public-health conditions have boosted life expectancy in developing countries, where most of the population growth is taking place, according to the U.N. data reported in the journal Science. The number of people globally reached 1 billion in 1800, then 2 billion in 1925, the report said. Within the last half-century, the population boomed from 3 billion to just under 7 billion. By 2050, the population will reach 9.3 billion, and 97 percent of the growth will be in less-developed regions, said Harvard economist David Bloom, who wrote the report.