Final answer:
The closest common ancestors of all humans lived in Africa until about 500,000 years ago, supported by genetic evidence showing all humans share common ancestors from Africa approximately 200,000 years ago. The 'out of Africa' model of migration is the most widely accepted, due to strong ties in human genomes to those in Africa.
Step-by-step explanation:
The common ancestors of all humans alive today lived in Africa until about B) 500,000 years ago. Genetic evidence from mitochondrial DNA (mtDNA) indicates that all humans share common ancestors who lived in Africa approximately 200,000 years ago. Early Homo sapiens first left Africa about 40,000 years ago and spread throughout Europe, Asia, and Australia, eventually reaching the Americas.
According to the 'out of Africa' model, modern humans emerged first in Africa and then expanded out of Africa, replacing all other human species. This model is supported by the fact that human genomes outside of Africa have close ties to African genomes and that there is a genetic variance found in Africa which is not found elsewhere in the world.
It is important to note that the 'multiregional evolution model' proposed that Homo sapiens evolved from Homo erectus in several places around the world at the same time, but this model relies more on fossil and archaeological records rather than on genetic data. The genetic data supports the 'out of Africa' model as the most likely explanation for human origins.