Final answer:
Genetic variation is greater within human populations than between them, with most genetic diversity found within individual populations. The greater genetic diversity in Africa is due to its older genetic lineage, confirmed by the Out of Africa model and the longer time for mutations to accumulate.
Step-by-step explanation:
The question of genetic variation within or between human populations can be answered in the context of human evolutionary history and genetics. Studies, such as the one conducted by Rosenberg et al. in 2002, have shown that within any given human population, there is considerable genetic diversity. This intrapopulation diversity is primarily due to differences in individual DNA bases within alleles. However, when comparing human populations, it has been found that the level of genetic variation is greater within populations than between them. Specifically, the majority of human genetic variation, about 85-90%, exists within populations, while only about 10-15% exists between different populations.
Moreover, regarding the wider genetic variation in the human population in Africa compared to the rest of the world, it is attributed to the older genetic lineage in Africa. This is supported by the Out of Africa model which posits that modern humans originated from Africa and then dispersed to other parts of the world. Consequently, African populations have had more time for mutations to accumulate, leading to a greater genetic diversity. Factors such as natural selection, allelic diversity, and environmental influences also continue to contribute to human genetic variation today.