Picture the Sahara.

Endless sand dunes, the sun beating down, and no  ice cold beverages in sight. But it didn’t always look that way.

Thousands of years ago, it was lush, green, and basically unrecognizable. And this paradise was also  home to human populations, but they’ve been really hard to study. Researchers have wondered who  they were, where they came from, and how they connected to the  other human societies at the time.

These are big questions, so you’d think that we would need lots of data to answer them. But it turns out that the key to  unraveling all of those mysteries was hiding in a cave, buried  in the DNA of just two people. [♪INTRO] It may sound odd to hear the  Saraha was once unrecognizable. After all, it’s the most iconic  desert in the world, filling nearly all of Northern Africa.  But it wasn’t always a desert.

Between 11,000 and 5,000 years  ago, it had trees, lakes, and significant rainfall. We call  that lost biome the Green Sahara. This time period is known  as the African Humid Period, part of a larger cycle of wet  and dry periods in the region that stretches back more than 5 million years.

These climatic changes are related  to the earth’s tilt and orbit, which shift slowly over long periods of time. Those tiny shifts caused feedback  loops between the climate and vegetation, and once those get going, the transition between wet and  dry periods happened really fast. At the start of a wet period,  the Earth is tilted in a way where the Northern Hemisphere gets more sun.

That increases surface temperatures, causing more evaporation and leading to heavier monsoons. More monsoons mean more water,  which leads to more vegetation. That vegetation absorbs more solar radiation, which raises the surface temperatures  and increases evaporation, leading to more monsoons, and so on.

Evidence from pollen and leaf  wax molecules suggests that this happened around 5000 years  ago, ending the African Humid period and creating the  Sahara Desert as we know it. But before then, you had lush grasslands with shade and plenty of permanent water sources. And when you have grasslands with shade and water, you have people.

Humans began settling in Egypt a little over 10,000 years ago, and continued to inhabit the Sahara until the rains  stopped 5,500 years ago. Archaeological evidence indicates  that the earliest of these societies were made up of hunter-gatherers  who may have domesticated some animals and even created  Africa’s earliest ceramics. Then over the next several thousand years, the people of the Sahara started  living with sheep, goats, and cows.

Those domesticated goats and  sheep were likely brought to the continent from Asia, when  people migrated in from Sinai and the Red Sea, later spreading  out over northern Africa. The hypothesis has been that  people from Northern Africa moved into the Saharan region when it  started going green, and later mixed with populations from the  Mediterranean and sub-Sarahan Africa. But this isn’t the easiest hypothesis  to test, because while some archaeological evidence exists,  the genomic data that would allow us to see how people are  related is in much shorter supply.

The dry, sandy, windy conditions  of the modern Sahara are absolutely terrible for preserving  DNA. So when human remains have been found, they typically  can’t be genetically profiled. To fill in the gaps in our  understanding, all archaeologists needed to find was one individual with  enough preserved DNA to sequence.

And in this case, they managed to find two. But before we get to that story, all research needs funding, including ours. So here’s a quick ad break!

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In 2003, archaeologists discovered a rock shelter in southwestern Libya called Takarkori. The site contained traces of  settlements spanning between 4,000 and 10,000 years ago, and was  a treasure trove for learning more about the people who lived  in this part of the Green Sahara. They found pottery shards  at the site that had traces of milk fat in them, which is  the oldest clear evidence of people in Africa milking  livestock for dairy products.

And way in the back of the  cave, there were human remains from 15 burials, dating from  between 8900 and 4800 years ago. Two of these were women in  their 40s, who both died about 7,000 years ago, during  that Green Sahara period. And as the Sahara dried out, so did their remains.

They essentially became natural  mummies, and the slow and controlled drying process meant  their DNA was preserved too. In 2025, researchers published  the results of a genomic analysis that revealed who  these women, and presumably the other inhabitants of the Green Sahara, were. It turns out that the hypothesis  about Northern Africa, Mediterranean, and sub-Saharan Africa mixing in  the region is most likely wrong.

The women had the most in  common, genetically speaking, with a group of people who lived in what’s now Morocco about 15,000 years ago. Even though Morocco would be part  of the Green Sahara eventually, this was millennia before the  African Humid Period began, so these Moroccan people  weren’t surrounded by greenery. So the fact that they were related  to the Takarkori population from 8,000 years later suggests that  the same lineage of people had been populating the region even before  it became a lush grassland.

Like their Moroccan relatives,  the Takarkori individuals share very little genetic material with  the people of sub-Sarahan Africa. So while we’ve known that the  Sahara Desert is a barrier to human migration today,  this suggests that it was a barrier even when crossing  it was far less dangerous. The two groups aren’t 100% similar though.

For starters, the Takarkori  women had less Neanderthal DNA. Neanderthal DNA is primarily  found outside of Africa, so the more of it that you find  in African peoples’ genetics, the more likely it is that that group mixed with non-African human populations at some point. The Moroccan population had about half as much as populations found around the Mediterranean, and the Takarkori individuals  had one tenth as much!

So the residents of the Green  Sahara were actually more genetically separated from  people from the Mediterranean than they had previously been, so they probably weren’t mixing with Mediterraneans, either. Which raises a whole new question, because their Moroccan ancestors hadn’t domesticated livestock. So where did the Takarkori people  get their dairy herds from?

Either the people of the Green Sahara managed to figure that out all on  their own, or they had contact with people outside of the region,  but in a totally platonic way. And because the pottery at  Takarkori resembles pottery found elsewhere in Northern Africa, these  researchers think it was the latter. So this DNA told us that despite  evidence of interaction and cultural exchange between  populations during the Green Sahara period, there wasn’t much in  the way of genetic exchange.

The area seems to be more of a melting pot of ideas, but not of populations. These two people helped us learn  about trade, agriculture, migration patterns, and the economies of  people living 7,000 years ago. So if you don’t feel like you can  make a big difference in life, there’s always the chance you will from beyond the cave.

I mean grave. [♪OUTRO]