Podcast: Dating an ancient hominid skull, and an ancient Antarctic rainforest

Host: Nick Howe

Welcome back to the Nature Podcast. This week, we’re diving into the ancient past and finding out about the almost century-long quest to date an ancient skull.

Host: Shamini Bundell

And we’re learning about an Antarctic rainforest from the Cretaceous. I’m Shamini Bundell.

Host: Nick Howe

And I’m Nick Howe.

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Host: Nick Howe

So, as regular listeners may be aware, we’re all working from home at the moment due to the ongoing pandemic so things will probably sound a bit different for the foreseeable future. Shamini, you’re on the phone to me now. How are you doing this week?

Host: Shamini Bundell

I’m alright. I’m enjoying being on the phone to you, Nick. I’m here at home. I’m buried under three blankets, a shawl and a duvet for maximum soundproofing.

Host: Nick Howe

Well, that sounds like very good soundproofing. Last time you sounded almost like you were in a studio, so I think you’ve got the soundproofing nailed. But on with the show, and first up, we have some breaking news – an ancient hominid skull in fantastic condition has been dug up… just 99 years ago. Okay, so, maybe this fossil hominid head isn’t a brand-new discovery, but researchers are still trying to unravel the secrets of the Broken Hill skull, in spite of having had a century to study it since it was dug up in a metal ore mine in what is now Zambia.

Interviewee: Chris Stringer

It was a complete chance discovery. The site had been mined for many years, and the miners regularly reported finding bones.

Host: Nick Howe

This is Chris Stringer, a researcher of human origins at the Natural History Museum in London. Chris and his teammates have been trying to shed light on one of the key questions about this relic – where it fits into human history. Does the skull signify a member of the line that led to Homo sapiens? Or is this more of a long-lost cousin? Reporter Adam Levy got in touch and kicked off by asking what’s so special about this century-old fossil?

Interviewee: Chris Stringer

It’s a beautifully prepared fossil. It’s one of the best-preserved of all human fossils. It was sent to the Natural History Museum in 1921 and was published soon afterwards in the journal Nature and named as a new human species, Homo rhodesiensis.

Interviewer: Adam Levy

And what was understood to be the significance of this skull and the species that it represented?

Interviewee: Chris Stringer

Well, when it was discovered, of course, it was the first important fossil human to be found in Africa, so that was of great significance, and in recent years, the species that it’s generally assigned to - Homo heidelbergensis – occupies a really central place in human evolution as a possible ancestor for our species and the Neanderthals.

Interviewer: Adam Levy

This is a fossil that was dug up almost 100 years ago now, but understanding actually when the human who it belonged to was walking the Earth, that’s proved quite difficult, right?

Interviewee: Chris Stringer

Yes, because of the circumstances of discovery, the fact that this was a metal ore mine so the discovery was completely uncontrolled. There was no systematic excavation at the time, so that’s been one of the problems, and estimates of its age have ranged from as young as 50,000 years to as old as 1 million years.

Interviewer: Adam Levy

Now, of course, that’s not the end of the story because otherwise I wouldn’t be phoning you up right now. What was the experience actually like of trying to pin down a date on this skull?

Interviewee: Chris Stringer

Well, of course, it’s been, in many ways, a frustrating experience trying to date the Broken Hill skull because we’ve been working on this project with colleagues for about 20 years, and the more we did, the more we came to realise that the skull must have been deposited and fossilised in a different part of the cave system than everything else that we tried to measure, so it was very frustrating. It meant that we couldn’t get a good proxy by dating something else. In the end, we had to try and date the skull itself because the associated materials were different ages and were uncertainly associated.

Interviewer: Adam Levy

So, yeah, you’ve got all these kind of associated materials which don’t show the age of the skull. How do you now investigate the skull itself?

Interviewee: Chris Stringer

Right, yes, well, we applied direct uranium-series dating to the skull itself. Many years ago, you’d have to take a large chunk of a fossil to do this kind of dating. Whereas now, the method is miniaturised and you can use laser ablation, so tiny pinpoint holes are made, and the best age estimate we can come up with is that the skull is around 299,000 years because that age of 300,000 not only being quite young, it also suggests that Broken Hill was living in Africa alongside other human lineages, other human species. Because we’ve got sapiens-like fossils in places like Morocco and Kenya at about 250-300,000 years ago. It’s a much more complex picture of different human lineages co-existing, and our line of evolution is only one of these, if you like, experiments in human evolution that’s going on across the Old World.

Interviewer: Adam Levy

What does that actually tell us, I suppose, to know that there were all these different humans walking about at the same time as each other? Does that change our picture of our history, of our ancestors’ history?

Interviewee: Chris Stringer

Well, certainly, it changes it in several ways because, of course, it means that we aren’t, in that sense, special. If you could have travelled back in time 300,000 or 500,000 years ago, you may not have picked the Homo sapiens line as the one that was going to survive and take over from all the others.

Interviewer: Adam Levy

Another thing I noticed in the paper which really would seem to turn some ideas on their head was this idea that a lot of the stone tools we’re finding maybe can’t be credited to our ancestors.

Interviewee: Chris Stringer

Yes, these Middle Stone Age tools have been found at Broken Hill, so Broken Hill, the Broken Hill people may have been making Middle Stone Age tools, so it means that that industry was not the unique product of Homo sapiens. When we find it somewhere, we can’t automatically assume that Homo sapiens was the maker of those stone tools.

Interviewer: Adam Levy

Now, it’s already 100 years since this skull was dug up. Do you think at this point that’s the end of the story or do you think there are more secrets to come from the Broken Hill skull?

Interviewee: Chris Stringer

Oh, I’m sure it’s not the end of the story because, of course, dating methods are improving and changing all the time. There could be completely new dating methods in the future that could be applied to the skull. It’s possible that we could get proteomic evidence. So, proteins can survive where DNA doesn’t survive, so for Broken Hill, if we can get fossil proteins out of the Broken Hill specimen, we can actually start to relate it directly to some of these other species, and test our ideas of evolutionary relationships.

Host: Nick Howe

That was Chris Stringer of the Natural History Museum in London here in the UK talking with reporter Adam Levy. To find out more about the Broken Hill skull, head over to nature.com, or we’ll put a link to the paper in the show notes.

Host: Shamini Bundell

Later on, we’ll be taking another trip to the ancient past to learn about a rainforest near the South Pole. Right now, though, it’s time for the Research Highlights, read to you this week by Noah Baker.

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Noah Baker

A new type of blood test can help detect early signs of up to 50 types of cancer. Researchers collected blood samples from more than 2,000 people with cancer and a similar number from healthy individuals. Then they scoured the samples for DNA that had entered the bloodstream and probed it for chemical indicators of cancer. The authors then developed an algorithm to predict the presence of cancer on the basis of these chemical fingerprints. For some of the deadliest cancers, like pancreatic cancer, the algorithm could detect tumour signatures in 39% of people at early stages and 92% in those with advanced cancer. The test could also predict which tissue the cancer had originated in in 96% of cases. The authors say that this simple way to detect multiple types of cancer and identify a tumour’s location in the body could make successful treatment more likely. Detect that research in the journal Annals of Oncology.

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Noah Baker

Your brain is soft and squishy. I don’t mean that as insult – everyone’s is – but it does mean that hard brain implants can damage it. But now, researchers from MIT have developed soft implants for our soft brains. Implants can ease the symptoms of brain disorders, but typically they cause inflammation or the build-up of scar tissue. By combining nanowires with a special solvent, researchers have made a gel-like, electrically conductive substance that could be used instead. This new material was used to successfully monitor a mouse’s brain activity, and could even be 3D-printed. The researchers hope that this proof of concept will allow others to rapidly develop their own implants to help treat neurological disorders. Implant that research directly into your soft brain in Nature Communications.

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Host: Shamini Bundell

Next up on the show, we’re travelling south… far south to latitudes near to the South Pole. It’s a pretty cold and icy place right now, but it wasn’t always that way. This week in Nature, a team of researchers have been finding out about the very different climate and ecology that was there in the Cretaceous period about 90 million years ago. Reporter Dan Fox called up Johann Klages, who led the research, and started by asking him exactly where this research was done?

Interviewee: Johann Klages

Where we work is currently the most rapidly changing part of the Antarctic Ice Sheet. The glaciers are retreating at an accelerating pace. We took a drilling device, a seafloor drilling device, that allowed us to drill deeper and to also, at the same time, go deeper in time and see into time frames of Antarctica that looked completely different than what we see today.

Interviewer: Dan Fox

And what did you find when you dug deeper?

Interviewee: Johann Klages

We drilled into completely different stuff which was full of fossil roots, of very fine material bearing diverse taxa of pollen and spores, and we knew we had something very special.

Interviewer: Dan Fox

So, what do these pollen and spores reveal about the environment during this period?

Interviewee: Johann Klages

It must have been an environment like a swampy, temperate rainforest environment. Antarctica was much warmer than we knew before and than we expected. Today, the latitude of the drill location is about 73 degrees south, but 90 million years ago it was 82 degrees south, which means that it’s only 900 kilometres away from the South Pole. And we had a mean annual temperature of 13 degrees Celsius, which is warmer than the annual mean temperature of Germany right now, and we had summer temperatures of around of 20 degrees Celsius in the air but also in the surface water.

Interviewer: Dan Fox

So, what sort of things could have been living in this swampy rainforest?

Interviewee: Johann Klages

It was a diverse environment, full of plants and you have to assume that in this kind of environment you had, of course, dinosaurs, you had insects because we also have the pollen record of the first flowering plants that far south. So, no one knew before that flowering plants went so far south.

Interviewer: Dan Fox

And so, just to get a kind of real image of this rainforest – ignoring the dinosaurs, obviously – was there somewhere on Earth right now that would be of a similar appearance or makeup?

Interviewee: Johann Klages

I think the closest environment you would look at would be the South Island of New Zealand and on the South Island to the north-western part. There you have pretty coastal, near-temperate rainforests. But we have to emphasise this – we don’t really have a modern analogue for what we found because if you look at latitudes of 80-82 degrees north or south right now, it’s pretty icy.

Interviewer: Dan Fox

Yeah, and one other thing I know about the polar regions is that they’re dark for a lot of the year, so how do you think this kind of verdant ecology survived in those conditions?

Interviewee: Johann Klages

One of the main drivers is CO2, and CO2 not in concentrations we see right now from just about, let’s say, what do we have right now, 400-410 ppm. No, you need something around 1,200-1,700 ppm CO2 in the atmosphere to get something like that.

Interviewer: Dan Fox

And my last question is with global warming, are we likely to see this sort of vegetation at the South Pole again any time soon?

Interviewee: Johann Klages

We have to keep in mind that the plate tectonic or configuration at the time was completely different than it is today, but at the same time, we do also everything to emit a lot of CO2 in the atmosphere, and what we showed is that excessive amounts of CO2 can be very powerful. I could imagine that we get close to CO2 levels where things will get pretty interesting, but to get a similar environment close to the South Pole like we reconstructed now, I think this is pretty unlikely. But at the same time, it shows us this already happened on the planet. We had that already. This is not fiction. This happened. It makes us aware of how fragile and flexible our planet is, and of what can happen when things go out of control.

Host: Shamini Bundell

That was Johann Klages of the Alfred-Wegener-Institut in Bremerhaven, Germany. You can find Johann’s paper over at nature.com or there will be a link in the show notes. And if you’re interested to see some of what Johann found deep under Antarctica, then we’ve also made a video for you. Check that out over at our YouTube channel –youtube.com/NatureVideoChannel.

Host: Nick Howe

Finally on the show, it would be time for the News Chat, but as I’m sure you know, everything is a bit coronavirus-focused at the moment. Fear not though, we’ve got a new show, Coronapod, which will update you on everything coronavirus, and that’s coming out on Friday.

Host: Shamini Bundell

For now, though, Noah Baker is out in a field in rural England doing his permitted daily hour of socially-distanced exercise, and while he’s at it, he’s got another Research Highlight for you.

Noah Baker

I’ve opted for a gentle walk in the countryside for my exercise today because new research suggests that the more steps I take, the lower my risk of dying of heart problems, cancer and other diseases, regardless of how intensively I walk. The new study focuses on a diverse group of almost 5,000 adults who wore accelerometers for three years to measure their physical activity. The researchers then used death certificates to determine which of the participants had died over the following eight years. People who took more steps each day had a significantly lower risk of death than those who walked for less. But it seems that steps per minute didn’t influence mortality at all. The team do say, however, that their results don’t provide conclusive evidence that more daily steps cuts the risk of death because they only observed habits rather than intervening to control them. Oh, well, maybe that’s enough for this walk then. You can find that study over at the Journal of the American Medical Association.

Host: Nick Howe

That’s it for this week. You can keep in touch with us on Twitter – we’re @NaturePodcast – or you can send us an email to podcast@nature.com. We’ve been posting pictures on Twitter of our home-work setups, so feel free to send us some of your own, or send us any tips for quarantine that we can share.

Host: Shamini Bundell

And don’t forget, if you want to see the roots of that ancient Antarctic rainforest for yourself, I’ve got a video for you over at youtube.com/NatureVideoChannel. I’m Shamini Bundell.

Host: Nick Howe

And I’m Nick Howe. See you next time.