Final answer:
Genetic data, including mitochondrial DNA and the Y chromosome, indicate that all humans have common ancestors from Africa, supporting the Out of Africa theory of human expansion. This, along with genetic diversity and indirect evidence from human parasites, helps reconstruct how modern humans migrated out of Africa and spread across the world.
Step-by-step explanation:
Genetic data allows us to reconstruct the expansion of modern humans out of Africa through the analysis of genetic variances and the common ancestry of mitochondrial DNA (mtDNA) and the Y chromosome. This genetic information suggests that all humans share a common ancestor who lived in Africa approximately 200,000 years ago. The Out of Africa theory is supported by genetic research indicating that as early humans left Africa around 100,000 years ago, they spread globally, interbreeding with other human species such as the Neanderthal. Moreover, the greater genetic diversity found in Africa points to a longer established genetic lineage there compared to other world populations.
Interestingly, our relationship with parasites such as lice also provides genetic clues to our past, informing us about when humans developed certain habits like wearing clothes. Together, both the direct genetic lineage through our own DNA and indirect evidence from coevolving species contribute to a more comprehensive understanding of human migration and evolution.