Our collective family tree has a mysterious new branch
Hi there, thanks for joining us once again for Plain English. This is episode 239 for Thursday, March 5, and all your episode resources can be found at PlainEnglish.com/239.
Coming up today: By analyzing the DNA of living men and women in today’s West Africa, scientists have discovered genetic traces of a new branch of humanity that hundreds of thousands of years ago. In the second half of the episode today, we’ll talk about the English phrase “for the most part.” And the video lesson on the website, for Plus+ members, is about how to use “neither” and “nor” together in a sentence. You’ve probably heard both those words, but in this video lesson, I show you how to use “neither” and “nor” together. That’s at PlainEnglish.com/239.
Human DNA hints at ‘ghost’ ancestor
Scientists have discovered a mysterious new ancestor far, far back in human history. The interesting twist is that they made this discovery not from studying fossils, but from studying the DNA of humans living in West Africa today.
Our origins—the origins of the species homo sapiens—is not a straightforward history. We have a complicated lineage, in other words. From studying fossils, it’s known that homo sapiens branched off from other hominids about 600,000 years ago. When I say “branched off,” I mean that a single species divided and took different evolutionary paths and eventually developed into multiple species. The Neanderthals, the Denisovans, and what became today’s humans all took different evolutionary paths over several hundred thousand years. The Neanderthals and Denisovans went extinct about 40,000 years ago, leaving only homo sapiens from the original branch.
Though the three were distinct species, there is evidence that they cross-mated—in other words, they occupied some of the same land area and quite commonly mated with each other. The evidence of this lives in both fossils and in our own DNA. If, like me, you have non-African ancestors, then about 1.5 to 2.1 percent of your DNA is inherited from the Neanderthal species.
Until recently, our knowledge of our lineage came primarily from the study of fossils. But with rapid advances in understanding DNA and the human genome, scientists are able to make discoveries about our lineage without physical fossil evidence. And that is how they found a “ghost lineage,” or another previously unknown species that mated with early homo sapiens. It’s called a “ghost” because scientists can see it’s there because some modern-day humans carry traces of their DNA, but there is no physical evidence that they existed.
How did they find this? The researchers performed a statistical analysis of living human DNA, Neanderthal DNA, and Denisovan DNA. They drew human DNA from hundreds of people from a variety of African regions. For the most part, what they saw fit with our current understanding of human evolution. However, some people in the study had genetic variants that were not present in other humans, Neanderthals, or Denisovans. Specifically, three populations of West African people from parts of Nigeria and Sierra Leone have between two and nineteen percent of their DNA that is not explained by our understanding of human history or the history of other similar species.
The two scientists think the new ghost species interbred with humans about 50,000 years ago—about the same time that humans and Neanderthals were also interbreeding. But it’s not yet clear where in the ancient family tree this new species falls. It may be a branch of another species, homo erectus, which branched off from early humans about a million years ago.
Fossils from the earliest humans date back 300,000 years and archaeologists are discovering new fossils in Africa that continue to fill in gaps in our knowledge of human history. However, much of the earliest human history took place in Africa—and DNA degrades quickly in tropical climates.
The next steps in this research are to sequence the genomes of more people in Africa and to perform additional testing on fossils.
It is an exciting time to be studying early humans. The earliest discovery of a Denisovan bone was in 1984, but the species wasn’t confirmed until 2010 after DNA testing showed that it was its own species. In the mid-2000s, a skull was discovered in Nigeria that is neither human nor Neanderthal. Further DNA testing on this skull will determine whether it belonged to this newly-discovered ghost lineage.
I know from Instagram that some of you have read the book “Sapiens: A Brief History of Humankind.” I don’t know why, but that must be the most Instagrammed nonfiction book out there—in English and in other languages.
Hey, life can get pretty busy at times, so you’d be forgiven for missing an episode now and then. If that ever happens to you, then you might like to get the episode emails. JR sends them out every Monday and Thursday morning and they have a summary of the episode. I think this is helpful because you can read the summary before you listen—that way, you have an idea of what the episode is going to be about, maybe think about it a little before listening in English. That’s what I would do—just read the summary ahead of time to warm up a little before listening to the episode. If you’d like to get those emails, then sign up at PlainEnglish.com/Mail.
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