Anthropological explanation that compares and contrasts the multi-regional and replacement models for the spread of Homo sapiens. And, provide are testable implications for each?

Question

This question demonstrates the students' understanding of the two theories provide scientific explanation of how Homo sapiens migrated. First, within Africa and the around the world.

Answer 1

Hello! Good question!

First, what are these hypotheses hypothesizing about? All hypotheses serve as guesses as to how/why a natural phenomenon is occurring. Both the multi-regional and replacement hypotheses are guesses about how early humans evolved, how they managed to disperse across the Old World, and why there are no other extant (alive today) human species.

The multi-regional dispersal hypothesis proposes that early Homo species (such as Homo erectus) migrated throughout the Old World (Africa, Europe, Asia, and Australia), where they interbred and shared genetic material with local hominids. This interbreeding led to a combination of the migrants and the locals to form Homo sapiens. The differences we see in genetic material between different geographical populations of the world are thus due to ancestral populations interbreeding with different hominid populations.

The replacement hypothesis proposes that Homo sapiens evolved in Africa, and then dispersed to the rest of the Old Word, outcompeting and replacing existing local hominid populations. This hypothesis allows that some interbreeding may have occurred between migrant and local populations, but not to the degree proposed by the multi-regional hypothesis.

These two hypotheses lead to two different testable predictions regarding genetic variability of human populations. The multi-regional hypothesis proposes that genetic variation between modern human populations is due to different interbreeding of ancestral populations. If that is true, we would predict that all human populations would be equally varied from each other, as all human populations would have interbred with equally different hominid populations. The replacement hypothesis proposes that genetic variation arose from independent evolution of different human populations once they migrated to new areas and became isolated, and that all human populations outside of Africa are descendants of the same original migrant population. If this is true, non-African populations should be more closely related to each other, genetically, than they are to African populations.

To test this, we can compare genetic sequences of individuals from many global populations. If we see equal variation between all populations, we have support for the multi-regional hypothesis. If we see a closer relationship between non-African populations, we have support for the replacement hypothesis.

Hope this helps! Let me know if you have any further questions.

Rebecca S.

Evolutionary Anthropology, Duke University