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Now, it's time to talk about fire.

In the early 1980s, archaeologists working at a site in Kenya called Koobi Fora noticed

some peculiar markings in the land they were excavating: distinctive patches of reddish-orange

sediment.

This wouldn't have been all that exciting, except that those patches looked a lot like

the patches of baked earth left behind by the campfires made by modern people in the

area.

Interestingly enough, this site had also turned up the jawbone of a fossil hominin and evidence

of stone tools having been made there, about 1.6 million years ago.

So this got the researchers thinking: Was it possible that these red patches were the

signs of an ancient fire that was used by some of our distant ancestors, more than a

million and a half years ago?

Well, maybe. There are still some big questions to answer.

Like, could the hominins at this site have actually made fire? Or did they happen to

find some fire occurring naturally, like from a lightning strike, and just used it for as

long as they could?

It's likely that our ancestors started out this way, taking advantage of fire as a fleeting

natural phenomenon.

But eventually they took it one step further-- scavenging a burning twig left behind by a

wildfire, and using it to start their own fires.

The use of fire wouldn't become truly visible in the archaeological record until it became

widespread - when fire started to be used consistently, across many different sites.

This could've been the moment in our history that sparked evolutionary change, triggering

an expansion into new environments.

And when we learned how to actually make fire when we wanted, it would forever change

our relationship with the world around us.

Now, the fact is, we don't know exactly when hominins harnessed the power of fire.

And we're not totally sure what species among our ancestors was the first to master

it -- although there's one candidate that seems most likely. And it wasn't us.

Nevertheless, we do know that the ability to make and use it has fundamentally changed

the arc of our evolution. The bodies we have today were, in many ways, shaped by that time

when we first tamed fire.

The use of fire in human history is notoriously difficult to study, because fire is ephemeral.

It's more difficult to see in the archaeological record than, say, stone tools, because it's

a transient phenomenon that leaves little evidence behind. Ashes can easily blow away

in the wind or be washed away by water.

But we know that the use of fire has had enormous impacts on our bodies and our behavior.

So some experts have looked at the gradual changes in how hominins looked, and how they

lived, to hypothesize which of our ancestors may have mastered it.

The first impact that fire has had on our evolution is that it allowed us to cook food.

And it's hard to overstate how important that was.

The main advantage of cooking is that it breaks down food, making it easier to chew and digest.

You can actually think of cooking as a way of starting the process of digestion, before

you even put the food in your body. Which sounds gross when I put it like that.

It's actually delicious

But heat causes the large, complex molecules in food to break up into smaller, simpler

nutrients.

So if you heat food with an external source of energy, like fire, then you're saving

the energy that your body would have to put into chewing and digesting the food if you

had eaten it raw.

Cooking also breaks down toxins in plants and kills pathogens. And again, this saves

your body from having to invest energy in defending itself from poisons and disease.

Together, these things make cooked foods much more energetically efficient than uncooked

foods, so you end up getting more calories out of what you eat. And when you're trying

to survive, every calorie counts.

But of course, the other advantage of fire is that it like … keeps you warm. And so the

use of fire likely helped our ancestors expand their geographical range, migrating to places

with different climates and opening up a whole new world of ecological possibilities for

our species.

Now, there's one hominin, besides us, that fits both of these descriptions -- a species

that needed a lot of calories and that had to live in lots of different environments

-- and that's the earliest definitive member of our genus, Homo erectus.

Some anthropologists propose that Homo erectus might have been able to cook food, based on

its physical adaptations.

Specifically, it had smaller teeth than its predecessors, suggesting that it didn't

need to do the heavy-duty chewing that a diet of raw food would require.

But maybe more importantly, it also had many of the traits that we know require a lot

of calories -- like a larger body size, more muscle mass, and most importantly, a larger

brain.

And as for its ability to live in different environments, Homo erectus is the first hominin

known to have migrated out of Africa, eventually spreading from what's now the Republic of

Georgia all the way to Southeast Asia.

But here's the problem: Homo erectus dates back about 1.89 million years.

But the earliest possible evidence of repeated, regular cooking doesn't show up until hundreds

of thousands of years after its appearance.

Likewise, Homo erectus began its excursions out of Africa hundreds of thousands of years

before the first definitive evidence of widespread fire use.

So how could fire have helped this species develop a bigger body and brain, and help

it migrate to other places?

Well, as in many aspects of studying the distant past, there are a lot of dots to connect.

And in this case … we're just missing a lot of dots.

So let's look at what the evidence does tell us -- about the use of fire in general,

and then cooking specifically.

In the past few years, anthropologists have gone back to that red-stained site in Koobi

Fora, Kenya. And recent excavations have turned up more definitive evidence of fire use than

those red patches of earth found in the 1980s.

Archaeologists have discovered shards of rock with tell-tale signs of having been heated

to high temperatures, as well as bits of burned animal bone.

And these bits of rock and bone seem to be clustered in distinct patches. Which is important,

because it suggests that the fires were small and made intentionally, and not a natural

wildfire, which would have burned across the whole site.

As for who made these fires, the burned rocks and bones were all found in an area associated

with artifacts that were likely made by Homo erectus.

But there aren't any remains of those hominins to be found there. Instead, the only hominin

fossils from the site are of Paranthropus boisei, a smaller brained species.

The next earliest site with /widely-accepted/ evidence for fire is a site in South Africa

that dates back 1 million years, in a place called Wonderwerk Cave.

There, archaeologists have found burned bones and plants, as well as the larger and more

complex stone tools, like hand axes, that are known as Acheulean tools.

These tools have often been associated with Homo erectus. And some experts have speculated

that, based on the date as well, Homo erectus may be the hominin that built those fires.

Other more recent evidence of fire has been found at a site in Israel called Gesher Benot

Ya'aqov.

And there, at a site that's about 790,000 years old, burned seeds, wood, and flint have

been found clustered together into what researchers call phantom hearths - areas where fire might

have been, but without a neat campfire ring of stones.

These clusters, and the fact that they occur throughout time at the site, suggest that

the hominins who visited there were very familiar with fire and could create it any time they

wanted.

Again, no hominin fossils have been found there, but Homo heidelbergensis, a large-brained

species that might've been the last common ancestor of humans and Neanderthals, is one

candidate.

So that's what we know about when hominins used, and maybe made, fires. But things get

even more interesting when we try to figure out which of our ancestors was the first to

actually cook with it.

Those bits of burned bone found at Koobi Fora aren't necessarily proof that hominins were

regularly cooking meat 1.6 million years ago.

Instead, as with fire use in general, anthropologists are much more interested in when cooking became

widespread enough to actually influence our evolution.

And evidence for regular cooking behavior doesn't appear until very recently, at least

in geologic terms -- about 350,000 to 400,000 years ago, in the region of the Eastern Mediterranean

known as the Levant.

Here, another cave site, called Qesem, preserves a large, central hearth that was used repeatedly,

and which one group of researchers thinks was commonly used for roasting meat.

Hominin teeth found in the cave resemble those of both Homo sapiens and Neanderthals. But

whoever was cooking at Qesem, they left behind lots of butchered and burned bones.

Finally, there's still the question of when and where fire was used outside of Africa.

If fire was so helpful in fueling human migration, then can we track its use around the world,

to retrace our steps?

Well, the first species that we have fossil evidence of outside of Africa is -- you guessed

it! -- Homo erectus, at a site called Dmanisi in the Republic of Georgia, which dates back

1.8 million years.

But there's no evidence for fire at the site, even though winter temperatures likely

got just slightly above freezing.

And again, as with cooking, we only see really solid evidence for fire use in colder climates

much, much later -- at around 400,000 years ago in Europe, at two different sites.

At Beeches Pit in England, areas of burned sediment with heated stone tools and burned

bone have been interpreted as the remains of hearths. And at Schöningen in Germany,

the evidence is heated flints and charred wood.

These two sites have been suggested to be the work of Homo heidelbergensis, the same

potential fire-maker from Gesher Benot Ya'aqov.

But there are a lot of other hominin sites, both open-air and in caves, scattered across

Europe that /don't/ show evidence of fire, even though winter temperatures there couldn't

have been comfortable without it.

Those hominins must have found other ways to cope - maybe through other cultural adaptations

like clothes and shelter, or just cuddling a lot

or by migrating - being the Pleistocene equivalent of today's

snow birds.

So the origins and spread of fire in our evolutionary history remain full of paradoxes.

Like, how did Homo erectus evolve to have such a large brain and body without the bump

in energy and calories gained by cooking?

We see these changes in the anatomy of our ancestors before we see evidence of fire in

the archaeological record - though some researchers have suggested that we didn't need fire,

just good cutting tools, to start the process of breaking down meat before consuming it,

allowing us to efficiently extract more calories.

And how did this same species migrate out of Africa and into colder climates without

the warmth of a campfire? Dmanisi in the Republic of Georgia has a wealth of fossils, but no

signs of fire.

It seems pretty likely that the first fire made intentionally, by the hands of a hominin,

sparked to life somewhere in Africa, probably in an open-air site like Koobi Fora.

And maybe those hands belonged to a member of Homo erectus.

As with many other early chapters of our history, we have a lot more research to do.

But each of us lives with the legacy of that moment, captured in our own bodies. Our size,

our musculature, and our big, clever brains, are all influences from that time -- somewhere,

by someone -- when we first tamed fire.

Thanks for watching this episode of Eons, which is produced in partnership with PBS

Digital Studios and Complexly.

Complexly produces over a dozen channels, including Nature League, where host Brit Garner

explores life on Earth and questions what we think we know about the natural world.

For a taste of what you can expect, we've linked to their “Best of” playlist in

the description below.

Thanks for joining me today in the Konstantin Haase studio! And extra big thanks to our

current Eontologists, Jake Hart, Jon Ivy, John Davison Ng and STEVE!

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