Here on Eons, we often get asked to speculate   about how changes to the past  could’ve affected our present.

Like, what if the asteroid impact that ended  the reign of the dinosaurs just never happened?

Or, what would the world be like if bugs still   grew as big as they did back  in the Carboniferous period?

Nope, that's a big nope for me.

Or even, what would we be like if some of the   steps on our evolutionary journey  had gone a little differently?

We mostly don’t like to answer these questions,  because it’s usually impossible to know, and there   are plenty of wild things that actually did happen  in deep time that we’d rather tell you about.

Except for that last question - the one about  human evolution - we do kinda have an answer.

Because there was a group of hominins, those  creatures more closely related to us than to   chimpanzees, that did take a different,  parallel journey from our ancestors.

Our paths ran beside each other - and potentially   even crossed at times - but while ours  led us here, theirs led to extinction.

Our first introduction to this branch of the  family tree came in 1938 in South Africa,   when a teenage boy named Gert Terblanche  found some strange teeth and bits of a skull.

Word of this discovery reached  paleontologist Robert Broom,   who tracked down Gert at school and traded  him five chocolate bars for the teeth.

Like what?

Was he out of, magic beans, that day?

[laughs] He also convinced him to lead the way to the  site of the find, a place called Kromdraai.

There, Broom was able to piece together  practically the whole of the left side   of the lower half of the skull, along with  much of the jaw and nearly a perfect palate.

The skull Gert had found had wide  cheekbones and massive back teeth.

And while the skull was close in overall  size to that of a female gorilla,   some of its features pointed to a  much closer relationship with us.

Like, Broom could tell from the angle  of the skull’s connection point to the   spine that it would have walked more  upright than any chimp or gorilla.

He proposed that this was not  just a new hominin species,   but a whole new genus, one that he named  Paranthropus, meaning ‘beside human.’ And based on the bizarrely wide,  heavily-built proportions of the face,   the molars, and the jaw, he gave  it the species name robustus.

In the following years, many more fossils  of Paranthropus robustus have turned up at   nearby sites in this region of South Africa,  dating from around 1 to 2 million years ago.

But while robustus was the first  member of this genus to be discovered,   it wasn’t the last, or even the most  robust, Paranthropus to be found.

In 1959, paleoanthropologist Mary Leakey  found another species with similar,   but even more exaggerated traits,  this time in eastern Africa.

While excavating in Tanzania, she unearthed  and pieced together a nearly complete skull   with a massive jaw and huge molar  teeth twice the width of our own.

Plus, running along the top of its head was  a prominent line of bone called a sagittal   crest - a site where chewing muscles attach,  a feature that modern gorillas also have.

These traits initially suggested that  it would have been a champion chomper,   with massive enough molars and jaw  muscles to eat extremely hard foods.

The press termed it ‘Nutcracker man’  in their coverage of the discovery,   a nickname that has stuck ever since.

Scientifically though, it ended  up as Paranthropus boisei.

And based on the layer Mary  Leakey found the skull in,   it seemed to have lived beside our Homo  ancestors around 1.8 million years ago.

Even more recently, a third  Paranthropus species has also   been added to the group: Paranthropus aethiopicus.

First described in 1968 from eastern Africa, it’s  dated to a little over 2.5 million years ago.

This makes it the oldest of the three species,   and it’s considered to be a  possible ancestor of boisei.

Collectively, these three species are also  sometimes called “robust australopithecines.” But what was this side branch of the  hominin family tree actually doing?

They all share adaptations for powerful chewing  -- like wide-cheeked and heavily-built skulls   with prominent attachment sites for  jaw muscles and huge back teeth.

So, for a long time, a leading idea  was that, while this genus overlapped   in time and space with our early  Homo ancestors and close relatives,   they evolved a totally different strategy  for exploiting the same environments.

After our lineage diverged from  theirs some 3 to 4 million years ago,   our genus went in the direction of being  ecologically flexible generalists with   small teeth, big brains, and  complex tools and behaviors.

But our Paranthropus cousins went  in a completely different direction… Their brains stayed relatively  small - less than half the   size of a modern human’s - but their  molar teeth and jaws became massive.

Such big teeth and jaws allowed them to specialize   on hard and tough foods that other  hominins couldn't feed on as easily.

This is called niche partitioning,  and it allows different species   to coexist that might otherwise  compete for the same resources.

But what we’ve learned more recently is that  this picture is actually a lot more complicated.

For one, it now seems unlikely that these  robust hominins were all doing the same thing.

In 2019, for example, a study looking  at the patterns of microwear on the   teeth of robustus in South Africa and boisei in   eastern Africa found evidence that the  two species had very different diets.

See, different foods leave different  patterns of wear on the teeth,   with harder foods leaving more complex pitted  textures, and softer foods leaving long scratches.

And despite having similar anatomy, the tooth  wear indicated that while robustus was eating some   hard and brittle foods, boisei - the so-called  nutcracker man - actually had a much softer diet.

And a chemical analysis of boisei’s  tooth enamel has also suggested that   it was mostly eating what are called ‘C4  plants,’ like tropical grasses and sedges,   rather than nuts from trees and  shrubs which are ‘C3 plants.’ C3 and C4 plants use different photosynthetic  pathways to incorporate carbon into their tissues.

And for the record, C4 plants  do not actually explode.

'Cause I know it's gonna be  in the comments, you know?

And when an animal eats those plants, those  different carbon signatures can remain locked   in their tooth enamel for millions of years,  acting as a record of their ancient diets.

These carbon isotope records  show a clear difference - with   robustus eating mostly C3 plant  foods, and boisei mostly C4.

And in addition to there being more  diversity within the Paranthropus   genus than we once thought, it now also seems like   the differences between their genus and  ours might not be so clear cut either.

Stone tools, for example, are often thought  of as a hallmark of our genus, Homo.

But at a number of sites, stone tools and  Paranthropus remains have been found close   together, leading some researchers to argue that  they might have been making and using them, too.

And this may have allowed  Paranthropus to expand their diet,   and maybe even incorporate meat occasionally.

But the odds of tool-users fossilizing  while gripping their tools are…pretty low.

And thanks to the overlap between  Paranthropus and Homo at many sites,   we can’t tell who the stone tools belonged  to, and we may never know for sure.

So there are still a lot of open questions  about the diets, lifestyles, and behaviors   of Paranthropus, and we have relatively few  fossils of them that aren’t skulls or teeth.

And there’s nothing really like them around today.

They probably carved out a primate niche  that has been empty since their extinction,   leaving us without any similar  species to easily compare them to.

Which brings us to the inevitable question… Why did they go extinct and not us?

Well, one study published in 2023 actually tested  the idea that Paranthropus boisei was pickier   about its environment than early Homo that lived  at the same time, in the same general location.

The researchers used fossil bovids,  including various kinds of antelopes,   from the Koobi Fora formation in Kenya  to reconstruct the paleoenvironments   where Paranthropus boisei  and early Homo were found.

See, living bovid species  are often quite particular   about the kinds of environments they hang out in.

So when we find them in the fossil record,   they’re a useful indicator of what  the area was like at the time.

And based on these environmental  reconstructions, the researchers   concluded that early Homo showed up in more  different kinds of environments than boisei did.

This supports the idea that our ancient  ancestors were habitat generalists,   while our robust cousins were specialists.

And while we’re still trying to figure out what  their specialized niches actually looked like,   we know from modern conservation  studies and from the fossil record   that specialists are more likely  to go extinct than generalists.

They're less resilient to environmental shifts  that alter the availability of resources, and we   know that when they went extinct, the environment  was in the midst of this kind of shift.

Fossils of both boisei in eastern  Africa and robustus in South Africa   stop showing up around 1 million years ago.

And this was right in the middle of a period of   change in the Earth’s glacial cycles  called the Mid-Pleistocene Transition.

And there’s evidence to suggest  that eastern Africa saw its C4   grasslands shrink during this time.

This might’ve brought boisei into  more intense direct competition with   other herbivores and potentially even early Homo,   who could’ve exploited their  resources, too, when times were tough.

And in South Africa, evidence suggests  this Transition triggered the C3 woodland   habitats of robustus to shrink as well,  possibly driving them to extinction, too.

But, ultimately, we can’t say for  sure what happened to Paranthropus.

Which is a bit unsettling,  when you think about it.

Like,   in a lot of ways, our ancestors  weren’t so different from them.

They lived in the same places, at the same  times, and maybe even eating some of the same things.

They potentially encountered one another and may  have shared the same cutting-edge technology.

I see what you did there, 'cutting edge  technology', you and your stone tools...

They may also have given us genital herpes,  although that's a whole other story... buy me a drink and I'll tell you all about it.

The point is, we are still here…and they aren’t.

When we think about our evolutionary  past and the story of how we got here,   it’s often tempting to look at it  through a lens of inevitability.

Like, humans were simply ‘meant’ to  take the evolutionary path that we did,   evolve our unique combination of  traits, and survive into modern times.

But the parallel journeys of Homo and Paranthropus   show us that things could  have happened differently.