The First Exodus of Humans from Africa Wasn't Quite What We Expected
There are many twisted branches in the human family tree. It is difficult to separate the foliage in order to see the stem of our own species.
Cave paintings in Cederberg, South Africa. (dr322/Getty Images)
According to the traditional "out-of-Africa" theory, Homo sapiens descended from a unique lineage of early humans that appeared around 150,000 years ago before leaving for Europe and other continents.
But there is a different tale. Our family history may not be a single straight line tracing back through a slowly changing population, but rather a network connecting a diversity of families reaching throughout the African continent, according to a genetic study headed by academics at McGill University and the University of California-Davis.
The results are consistent with a multiregional scenario, according to which there was ongoing gene flow between at least two distinct populations before our species migrated from Africa to Europe.
According to Brenna Henn, a population geneticist at the University of California, Davis, "people who embraced the classic model of a single origin for Homo sapiens suggested that humans first emerged in either East or Southern Africa at different times."
However, it has proven challenging to reconcile these theories with the scant fossil and archaeological evidence of human occupation from places like Morocco, Ethiopia, and South Africa, which demonstrates that Homo sapiens were present on the continent at least 300,000 years ago.
The models included newly sequenced whole genomes from 44 Nama individuals who have historically lived in the region of Kuboes shown here, on the border of South Africa and Namibia. (Brenna Henn/UC Davis)
Southern Africa, Ethiopia, and Morocco are the places where the earliest fossils of our species have been discovered in Africa. Which of these areas, however, is the actual birthplace of humanity is unknown.
According to some scholars, this is a result of the incorrect assumptions we've made about our ancestry. Perhaps a patchwork of coexisting groups that have migrated and mixed has generated the stem of our species, which is actually a braid of branches.
There could be two main lineages responsible for the genomes of humans living in Africa today, according to a scenario of ongoing migration. These lineages represent various early human groups that existed in various regions of Africa circa 400,000 years ago.
The two populations may have united after evolving separately on opposite sides of the continent for a while, eventually fragmenting into subpopulations that survived from 120,000 years ago, according to models.
Researchers speculate that changes in wet and dry circumstances on the African continent between 140 and 100 ka may have encouraged these merging events across different stems.
They believe that this interwoven ancestry may have traveled from Africa to Europe 50,000 years ago.
Conceptual models of early human history in Africa. a) Recent expansion, b) Recent expansion with regional persistence, c) Archaic admixture, d) African multiregional (Ragsdale et al., Nature, 2023)
Although the genetic evidence did not quite support that. Models estimate that the first humans in Africa arrived in Europe 10,000 years later than they should have, according to comparisons with the genomes of people of European heritage.
However, recent research indicates that there may have been more than one wave of migration from Africa to Europe.
Genomic sequencing has developed into an extraordinary tool for researchers retracing the steps of our ancestors due to the limited fossil record for this period.
Genetic experts' stories and ours become more complex as more genetic data is read.