“Scientists from the University of Utah in Salt Lake City in the U.S. have calculated that 1.2 million years ago, at a time when our ancestors were spreading through Africa, Europe and Asia, there were probably only around 18,500 individuals capable of breeding (and no more than 26,000). This made them an endangered species with a smaller population than today’s species such as gorillas (approximately 25,000 breeding individuals) and chimpanzees (an estimated 21,000). They remained an endangered species for around one million years. Modern humans are known to have less genetic variation than other living primates, even though our current population is many orders of magnitude greater. Researchers studying specific genetic lineages have proposed a number of explanations for this, such as recent "bottlenecks", which are events in which a significant proportion of the population is killed or prevented from reproducing.”