Hugh Pickens writes: "Scientific American reports that researchers from the University of Utah have calculated that 1.2 million years ago, at a time when our ancestors Homo erectus, H. ergaster and archaic H. sapiens were spreading through Africa, Europe and Asia, there were probably only only about 18,500 individuals capable of breeding making humans an endangered species with a smaller population than today’s species such as gorillas and chimpanzees. Researchers scanned two completely sequenced modern human genomes for a type of mobile element called Alu sequences then compared the nucleotides in these old regions with the overall diversity in the two genomes to estimate differences in effective population size, and thus genetic diversity between modern and early humans. Human geneticist Lynn Jorde says that the diminished genetic diversity one million years ago suggests human ancestors experienced a catastrophic event at that time as devastating as a purported Toba super-volcano in Indonesia that triggered a nuclear winter and is thought to have nearly annihilated humans 70,000 years ago. "We've gone through these cycles where we've had large population size but also where our population has been very, very small," says Jorde adding that the reason the modern effective population is so much smaller than the current number of people (nearly seven billion) is that a population explosion occurred, probably due to the development of agriculture about 10,000 years ago."
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