He that sitteth in the heavens shall laugh...
Psalm 2:4
"The recent human evolution story is a quagmire of ever-changing
speculations that vary and conflict in their dates and geographical
specifics with each new paleoanthropological or archaic DNA sequence
discovery.
The current general consensus is often termed the recent
out-of-Africa model that postulates anatomically modern humans migrated
out of Africa about 100,000 to 200,000 years ago.DNA sequencing revealed that admixture between anatomically modern
humans and Neandertals and Denisovans had taken place. This was quite
surprising because:
1) Neandertals were not supposed to be part of the
African origins, and so were not supposed to be Homo sapiens;
and
2) Denisovans were completely unknown. RAO sub-models then quickly
began emerging to account for this inconvenient data. According to
recent reviews, four main human origins models now exist and compete
with one another:
- RAO (classic): Modern humans first developed in Africa about 100,000
years ago and then migrated throughout the world. Existing archaic
human populations (i.e. Neandertal and/or Homo erectus) in
various areas of the world were then replaced by the RAO migrating
populations, with little to no hybridization between the populations.
- RAO With Hybridization: This model is similar to the classic RAO above, but includes a greater level of hybridization taking place between the migrating populations and the indigenous archaic populations being encountered and displaced.
- RAO Assimilation: This model, like the other two above, accepts a recent African origin for modern humans. Unlike the previous two models, it includes replacement and/or extensive migration of populations as the major driving factor in the emergence of modern humans. This model focuses on the importance of pervasive gene flow and population admixture in conjunction with changing environmental conditions.
- Multiregionalism: This model denies a recent African origin for modern humans, based on biogeographical data that continue to emerge from paleontology and archaeology. This model also promotes the role of broadscale genetic continuity over time and gene flow between populations. The basic premise is that modern humans arose not only in Africa, but also in Europe and Asia from their H. erectus type Pleistocene ancestors.
If this quagmire of competing models was not confusing enough, researchers are at odds concerning the origins of modern human within Africa before the alleged global dispersion(s) ever occurred.
As noted by Henn et al. in 2018, there are four of these submodels competing with each other.
The first is known as African multiregionalism, which maintains that
there were multiple points of modern human origins across Africa, with
continuing admixture between populations.
The second proposes that there
was a single point of origin, with range expansions and local
extinctions, but with one line predominating.
The third proposes that
there was a single point of origin, with range expansion and one line
predominating, but slightly lesser-evolved populations breaking off
shortly before the dispersion, and occasional admixing.
The fourth
proposes that there was one point of modern human origins, with multiple
lines of archaic humans evolving side by side with a small amount of
admixture occurring shortly before the dispersal." CMI
