Everything Everywhere Daily: History, Science, Geography & More - Out of Africa

Starting point is 00:00:00 Several hundred thousand years ago, human beings walked out of Africa. What's been a subject of debate amongst anthropologists is why it happened, how it happened, and how many times it happened. The process by which Homo sapiens left their land of origin to populate the rest of the world has been one of the fundamental questions in anthropology. Learn more about the out-of-Africa hypothesis and the origins of humanity on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong?

Starting point is 00:00:41 throughline is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed. It effectively turned day into night and how it shaped the world now. Time travel with us every week on the Thurline podcast from NPR. The Out of Africa Hypothesis is perhaps more accurately called the Out of Africa hypotheses, as there are several different theories. What all the various theories are in agreement on is that humans originated in Africa. To understand the theories, it's helpful to understand the origin of our understanding of early humans. In the 19th century, after Darwin wrote the origin of species, we didn't have a lot of evidence for anything about early humans one way or another. Outside of modern humans, the only fossil

Starting point is 00:01:33 evidence we had was from Neanderthal or Homo erectus skeletons. That and comparative anatomy with other animals like chimpanzees and gorillas was it. Initially, it was assumed that all the early hominids that were discovered were not related to humans at all. As you'll see, the reason why theories of early humans have changed over time is that more and more evidence has been collected, primarily in the discovery of fossils, but also with improved techniques. In the 20th century, more and more hominid fossils were discovered. In particular, Australopithecus fossils were discovered in the 20s and 30s and homo-hydelbergenta skulls in the 1950s. Slowly, anthropologists began to put pieces together and assumed that these different species were in some way related. The theory which

Starting point is 00:02:19 came out of this in the 20th century became known as the multi-regional hypothesis of human evolution, also known as MRE. It was proposed in 1984 by Milford Walpaw of the University of Michigan. The multi-regional hypothesis, in hindsight, seems sort of silly. but it was the working explanation for the rise of modern humans for several decades. It held that different hominid groups left Africa several hundred thousand years ago and evolved separately. The similarities with other groups which became human were due to the sharing of genes between groups that bordered each other and migrations. Under this theory, modern homo sapiens didn't evolve in Africa per se, but it was a process that was undergone all over the Afro-Eurasian landmass.

Starting point is 00:03:04 The problem with this theory is severalfold. For starters, the odds that the same species would arise in different places and would be so similar is highly improbable. And it also assumed that most of the hominid fossils that were found in one way or another were ancestors of humans. The MRE theory wasn't the only one at the time. Another theory known as the recent African origin model was proposed in 1974. This theory held that modern Homo sapiens developed from one group in East Africa, and then spread out of Africa rather recently in the last 100,000 years or so. The thing which eventually resolved the debate to the satisfaction of most anthropologists was the new science of genetics. The advent of genetic testing allowed for a level of insight

Starting point is 00:03:50 that was previously impossible by just looking at old bones. If the multi-regional hypothesis was true, then humans should show signs of different ancient genes in different populations. If the recent African origin model were true, then we should only see a single set of older genes, and we should see genetic mutations timed as groups spread away from Africa. Here I should note that it is possible to approximately determine dates for genetic mutations over large populations due to a molecular clock that works inside of DNA. Mutations accumulate over time, and as techniques get better and better, it's possible to determine when genetic changes occurred.

Starting point is 00:04:28 There have been tens of thousands of human genome sequences of mitochondrial DNA which have been conducted on people all over the planet. These genomes all conclusively point to the exact same thing. All humans came from a similar group that originated in Africa about 200,000 years ago, and all non-African populations split apart within the last 50 to 60,000 years. If you remember back to my episode on mitochondrial Eve, this is approximately around the time when she would have existed, about 155,000 years ago. The genetic evidence was so overwhelming that the multi-regional hypothesis is, for the most part, dead. What it also did was put to rest the idea that all of the early hominid fossils which have been discovered were ancestors of humans.

Starting point is 00:05:17 What it showed is that many of them were just evolutionary dead ends. They weren't necessarily our ancient grandparents, rather they were our ancient cousins who moved to another city and we never heard from them again. Genetic testing also unveiled several other surprising things. For starters, Neanderthals weren't necessarily our ancestors, but they also weren't that far away from Homo sapiens genetically. There is evidence of Neanderthal DNA in almost all humans. The average human has about 2% Neanderthal DNA, with some populations having as much as 3%. The Neanderthal DNA is still making itself fell today. One particular genetic risk factor of COVID-19 was traced back to a fragment of Neanderthal DNA, which was found in European and South Asian

Starting point is 00:06:02 populations, but not nearly as much in East Asian and African populations. The confirmation of the recent African origin theory didn't end the story of how modern humans spread around the world. If you look at a map, you can see one small bit of land in modern-day Egypt, which connects Africa to the Middle East. The question is, if one group could have entered this area, then why couldn't others have as well, especially considering that we're talking about a period of time over 100,000 years. The answer is that is almost certainly what happened. Debates amongst anthropologists have shifted from the multi-regional hypothesis versus the recent African origin hypothesis to trying to nail down exactly when humans left Africa, how many times humans left Africa,

Starting point is 00:06:46 and the routes they took out of Africa. It turns out that while the recent movement of humans out of Africa was the origin of modern Homo sapiens, i.e. us, it wasn't the first out of Africa moment for related hominid species. Researchers have dubbed them out of Africa 1 and out of Africa 2, Electric Bugaloo. Okay, I added the electric boogaloo part, but that's really what they should call it. Out of Africa 1 was the migration of early hominids from 500,000 to 1.8 million years ago, and this would have included groups such as Homo erectus, homo-hydrogytus, and other groups, groups which all eventually died out. Out of Africa, too, was the migration of modern Homo sapiens out of Africa, starting with their appearance about 200,000 years ago. Out of Africa, too, which is really

Starting point is 00:07:34 the subject of everything I've been talking about so far, has become far more nuanced. It appears there were multiple waves of Homo sapiens migrations out of Africa. Not all of the migrations were necessarily successful insofar as they established permanent populations. A migration around 275,000 years ago might have included a species closely related to Homo sapiens, perhaps closer to Neanderthals. Fossils found in a cave in Greece date back 210,000 years. Modern human fossils found in the Arabian Peninsula in China date back about 85,000 years. These migrations of early humans may have resulted in populations that weren't successful. The migration, which definitely was successful, occurred around 70,000 years ago.

Starting point is 00:08:20 This took place some time around the massive Mount Toba explosion in Indonesia, which will be the subject of a future episode. This migration followed what was known as the Southern Route. They spread across Arabia, South Asia, East Asia, and Southeast Asia, including Indonesia, Papua New Guinea, and eventually Australia, all of which would have been connected by land during the Ice Age. Humans probably entered Australia about 50,000 years ago. Europe and North Asia were one of the last parts of Eurasia, to be populated. This was probably due to climate. Homo sapiens were a tropical species and stuck to warmer areas until they developed the tools to survive in colder climates. Homo sapiens entered

Starting point is 00:09:01 Europe around 40,000 years ago, where they also probably encountered Neanderthals and Denisovans. Humans didn't cross the land bridge into the Americas until about 20,000 to 15,000 years ago. The current genetic evidence points to a single group that migrated from East Asia slash Siberia, from which all native peoples in the Americas are descended. The story of human evolution and human migration is one that is constantly being updated as new evidence is found. Every year it seems that there are new fossil discoveries or new genetic research,

Starting point is 00:09:35 which helps to clarify the picture of how modern humans came to be. They are constantly adding pieces to the puzzle of how humans originated and how we are all related to each other. The one thing we can be sure of is that all of us, no matter who you are or where you're listening to this, have distant ancestors who came out of Africa. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Thor Thompson and Peter Bennett.

Starting point is 00:10:05 Today's review comes from listener KR. 687 over on Apple Podcasts in the United States. They write, Great podcast. This podcast has become my favorite. I've been catching up on older episodes and will be sad when I join the Completionist Club. I love the way you cover each topic. I always learned something I didn't know. Your podcast is good for the mind.

Starting point is 00:10:25 Thank you, Gary. Well, thank you, KR. 687. Don't be sad when you join the Completionist Club. Be happy to know that you have joined one of the most elite societies in the world. And also, you can always go back and listen to everything again. And that will get you upgraded to gold membership in the Completionist Club. Remember, if you leave a review or send me a boostagram,

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Everything Everywhere Daily: History, Science, Geography & More - Out of Africa

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