For example, Culex mosquitoes, which transmit West Nile and other life-threatening illnesses, are able to detect even minute concentrations of nonanal, a chemical substance given off by humans. Repellency effect of forty-one essential oils against Aedes, Anopheles, and Culex mosquitoes.
There were not many humans at this time, and they were spread out, rather than living close together. Experts think there were no more than one million humans living during any time of the Paleolithic Era. That might sound like a lot of people, but today there are about seven billion people, 7,000 times more people than in the Paleolithic Era. Archaeological evidence points to humans beginning in the continent of Africa, and later migrating to other continents.
6. How long ago did humans become human? The oldest known hominid, or humanlike species, has been dated at 4.4 million years old. Another species, which is yet to be confirmed as a hominid, has been dated at 6 million years old. Scientists estimate that the hominid lineage diverged from the ape lineage 5 to 8 million years ago. Homo sapiens, the species to which we belong, has existed for about 100,000 years.