According to scientists from the University of Utah, the entire human population of Earth was less than 26,000 for about a million years. Even fewer, about 18,500, were capable of breeding. This means that 1.2 million years ago, humans were an endangered species. Endangered species are species at risk of becoming extinct.
Scientists arrived at these estimates based on studies of genetic variation in ancient humans. Although the exact causes of such low numbers are not known, experts believe it may be due to various events that killed many people. One such suspected event is a nuclear winter, a period of very cold temperatures, caused by an eruption of a super volcano in Indonesia 70,000 years ago. Less than 15,000 people survived the disaster.
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