Final answer:
Human populations are not genetically isolated due to evidence from mtDNA, coevolution with other species like lice, the presence of Neanderthal DNA in modern humans, and the influence of cultural factors on gene flow and genetic variation.
Step-by-step explanation:
Evidence to show that human populations are not genetically isolated from each other includes genetic studies and fossil records which indicate gene flow and human migration throughout history. For example, mitochondrial DNA (mtDNA) studies suggest all humans share common ancestors from Africa 200,000 years ago. Additionally, the coevolution with organisms such as lice contributes to understanding the human story, as does the presence of Neanderthal DNA in modern populations, indicating interbreeding. Moreover, genetic variation is widespread within populations but comparably minor between different populations, challenging the biological significance of race. The rapid adaptation of genes in populations like Tibetans in just 8,000 years shows the dynamism of human genetics. Cultural factors, including migration and sexual selection practices, greatly influence gene flow and genetic variation within human populations. Together, these points underscore the extensive genetic connectivity among human populations globally.