Leaving Our Greatest Grandma’s Home (125 thousand years ago)
New species, subspecies, and races can form when a population become isolated from the rest of its species. They can also form when closely related species, subspecies, and races mix. The Ice Age cycles proved to be an species generator for humans. Populations would become isolated in north due to giant glaciers cutting off populations. In Africa, during ice ages, much of the continent became dry and barren. Since these deserts were difficult to cross, they also served to cut off populations from one another. While these conditions persisted, the populations “trapped” by deserts, glaciers, and coasts can mix over centuries and form new kinds of humans with different dominant traits. What we know as modern humans likely came into being after previously isolated populations in Africa, each holding one key modern human characteristic, came into contact with each other after an ice age ended as the deserts separating them disappeared, and mixed. The oldest Anatomically Modern Human that we know about lived 300 thousand years ago in Morocco. Modern humans were likely found throughout Africa at this time, although evidence is scarce. But then came another Ice Age age (the Penultimate Ice Age, the one right before the most recent one we’ve had, about 194 thousand years ago), and humans became separated from one another again, and new races of modern humans were created.
One enclave of humanity that existed was centered on the remains of the largest lake Africa ever knew, in the south central part of it, in modern day Botswana. Lake Makgadikgadi was a behemoth in its heyday, but then it started to drain slowly. The area it once covered became a network of interconnected small lakes and basically one huge wetland area. While much of Africa was a desert, the modern humans who were living here prospered. They could not leave this area though, because there was little vegetation beyond it. Of particular note, Mitochondrial Eve is thought to have been born in this area 200,000 years ago. She is basically all of our mother’s mother’s mother’s etc. mother. Everyone who is alive today can trace their maternal ancestry to her. Her mother had no other daughter whose maternal line survives to this day. There were many other women who lived at the same time as she did, but none of their maternal lines have survived to this day either. They may very well have descendants alive today, but only through at least one male descendant. The mitochondrial dna of every person alive today (which is only passed on from mother to child) is a copy (with possible mutations) of the mitochondrial dna of Mitochondrial Eve’s. It appears that the DNA of Mitochondrial Eve and the rest of the people living in this wetland enclave is similar to the San people. You may have seen the movie “The Gods Must be Crazy”? The hunter gatherers in that mockumentary are the San, and that movie happened to take place in about the same area that Mitochondrial Eve lived. So, it appears that we all are descended maternally from San people from 200,000 years ago.
Around 130,000 years ago, the Penultimum Ice Age came to a close, and the world entered the Eemian Interglacial, a time where the climate was much like it is today. Precipitation patterns started to change, and Africa began to become interconnected again. A “green corridor” of vegetation was formed to the northwest of the enclave. This allowed the people there to explore new lands in southern Africa. The Eemian ended and a new ice age began about 115 thousand years ago, but 5 thousand years later, a second green corridor opened up to the South West and the people of the wetlands headed to the coast of South Africa, where they likely encountered other modern humans who had survived the previous ice age desert conditions by exploiting marine resources. They then proceeded to survive much of the new ice age the same way. They also left footprints along the beaches and developed some advanced stone tool making techniques.
The people from the wetlands pretty much kept to Southern Africa until 70,000 years ago. During that period, other modern humans spread along the southern Indian Ocean coasts of Asia. Neandethals dominated in Europe, Denisovans in parts of Asia and the descendants of Homo Erectus in south east asia. At 70,000 years ago, a group of the people of the wetlands entered East Africa. From there, some left Africa 60,000 years ago and went into Europe, Asia, and Australia. Everywhere they went they encountered other modern humans and closely related human species. They mixed with the people they found and displaced them. The mitochondrial dna eventually replaced all the human mitochondrial dna found anywhere else in the world. This is a natural process that can happen when a larger population mixes with a smaller population over many generations. Some of these other populations still have descendants today, and we got some parts of our dna from them, but their mitochondrial dna has gone extinct. It’s quite a fascinating puzzle how one people came to dominate the whole Earth in this way though. Was there a biological advantage? A technological one? A cultural one? A lifestyle one? Were “we” just opportunistic and the other populations were in decline for some reason, such as the Mount Toba eruption, disease, or climate change? I guess the archaeologists will have to try to figure out that one.
Sources:
News stories -
Mitochondrial Eve 200ka (Sep 2010) https://www.sciencedaily.com/releases/2010/08/100817122405.htm
Isolated African Populations Coming Together (Aug 2018) https://www.sciencedirect.com/science/article/pii/S0169534718301174
Homeland (Oct 2019) https://www.sciencedaily.com/releases/2019/10/191028175138.htm
https://www.ancient-origins.net/news-history-archaeology/ancestral-homeland-0012784
https://www.insidescience.org/news/experts-skeptical-new-study-pinpointing-birthplace-humanity
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