The origin of modern humans is a much-debated topic, with various different suggestions on how we evolved. However, it is mostly agreed that Africa was the birthplace of modern human evolution. This idea was originally rooted in fossils but was later supported by archaeological and genetic data. Here, we will look at recent discoveries and the theories of modern-day human evolution.
The 'Out of Africa' model of evolution
The 'Out of Africa' model of evolution is the most widely accepted model for modern humans. The theory began with Charles Darwin in the 19th century and was based on the presence of chimpanzees and gorillas in Africa, as well as Huxley's investigations into anatomy, which showed that humans and apes have a common ancestor. This theory proposes that Homo sapiens evolved in Africa and then migrated across the world. Specifically, humans are thought to have evolved in East Africa and then moved across the globe around 70,000 years ago. It is believed that humans replaced, rather than interbred with, the archaic hominins that lived outside of Africa. There are discussions over the timing of the dispersal from Africa, and there is also an opposing theory called the 'multiregional model.
Over 150 years after Darwin proposed the theory, genetics using genome-wide genotyping, sequencing techniques, and archaeological evidence confirms the African origin of the first modern humans but also highlights other complexities. Researchers are now investigating when exactly the dispersal from Africa occurred and whether it happened in one wave.
The African origin of the first Homo sapiens is largely accepted, but there is debate over whether they arose from East, South, or North Africa. There is support for the emergence from East Africa in the form of fossils found in Ethiopia. However, genetic studies suggest an origin in southern Africa rather than archaeological studies. When different regions were examined genetically, it was found that Southern hunter-gatherers were one of the most genetically diverse populations, supporting the idea of a Southern African origin. North Africa was not initially a favored research area for determining where Homo sapiens arose, but after the publication of the Y chromosomal phylogenetic tree, there was more focus on the region. The phylogeny suggests that the deepest clades originated in Northwest Africa, indicating that this region could be more important than originally thought.
Another question regarding the distribution of modern humans is the route they took out of Africa. The main view is that if humans left Africa in one dispersal, they could have taken two possible routes. The northern route would have been through Egypt and Sinai, while the southern route would have been through Ethiopia, the Bab el Mandeb Strait, and then the Arabian Peninsula. Currently, there is no archaeological or genetic evidence to confirm either route.
The ’multiregional’ model of evolution
This model of evolution was suggested by Weidenreich in 1946 and spoke about a gene flow among subpopulations of Homo erectus dwelling in different parts of the world throughout the Pleistocene, meaning that modern humans can trace their ancestry back to various hominin groups living in multiple regions. This term is sometimes used interchangeably with the "candelabra" model. This model suggests that our early hominin ancestors, following their exit from Africa, independently evolved anatomically modern features. This model hypothesises that the modern human form arose autonomously at multiple times and places over the globe. Despite these terms, being used synonymously, this contrasts with the multiregional model, which does not allude to the independent parallel evolution of modern human features.
There is some fossil evidence supporting the multiregional and candelabra models. There was the discovery of the Dali Man in China. For those in favour of these hypotheses, the combination of archaic and modern features was support for a midway stage between early and modern hominins. However, these fossils are not well preserved, and it has been suggested that these anatomical features are actually shared by other Homo and were therefore not unique to Asia.
Whilst there are different suggestions as to the origins of modern humans, it is currently unclear as to our exact dispersal. There may be wisdom to take from each model of evolution, and there will certainly be lighter shed on our past with the advancement of archaeological and genetic studies.