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Oldest African burial site uncovers Stone Age relationship with death

Listen to the latest science news, with Benjamin Thompson.

Listen to our mini-series ‘Stick to the Science’: when science gets political and vote for the show in this year’s Webby Awards.

In this episode:

00:44 Human burial practices in Stone Age Africa

The discovery of the burial site of a young child in a Kenyan cave dated to around 78 thousand years ago sheds new light on how Stone Age populations treated their dead.

Research Article: Martinón-Torres et al.

News and Views: A child’s grave is the earliest known burial site in Africa

09:15 Research Highlights

How warming seas led to a record low in Northwestern Pacific typhoons, and the Arctic bird that maintains a circadian rhythm despite 24 hour sunlight.

Research Highlight: Warming seas brought an eerie calm to a stormy region

Research Highlight: The world’s northernmost bird is a clock-watcher

11:35 A metal-free rechargeable battery

Lithium-ion batteries have revolutionised portable electronics, but there are significant issues surrounding their recyclability and the mining of the metals within them. To address these problems, a team of researchers have developed a metal-free rechargeable battery that breaks down to its component parts on demand.

Research Article: Nguyen et al.

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doi: https://doi.org/10.1038/d41586-021-01221-6

Transcript

Listen to the latest science news, with Benjamin Thompson.

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, uncovering the earliest evidence of deliberate human burial in Africa, and a metal-free, amino-acid based rechargeable battery. I’m Benjamin Thompson.

[Jingle]

Host: Benjamin Thompson

First up on the show this week, the way that people commemorate and bury their dead – so-called mortuary practices – are in enshrined in culture and tradition all over the world and throughout history. And this week in Nature, a paper describes a very rare archaeological find that’s shedding light on ancient burial practices in sub-Saharan Africa. Reporter Adam Levy has been finding out more and, just to let you know, this story discusses the burial of a child.

Interviewer: Adam Levy

In 2017 in a cave in Kenya, archaeologists uncovered a find which would reveal an intimate snapshot of human behaviour tens of thousands of years ago.

Interviewee: Maria Martinón-Torres

This finding has been an amazing adventure, I would say, for those who like to investigate the past.

Interviewer: Adam Levy

This is paleoanthropologist Maria Martinón-Torres. The adventure would shed light on a subtle, deeply human part of our history – how we respond to death – and yet the scientists didn’t learn the significance of what they had found right away.

Interviewee: Maria Martinón-Torres

The archaeologists discovered an accumulation of very degraded and fragile bones that were all together in a sort of pit in the site, and those bones were so fragile and they were so brittle that it wasn’t possible to properly excavate them.

Interviewer: Adam Levy

Instead of delicately excavating each of the bones on location, the remains were transported wholesale to the lab where they could be handled much more carefully.

Interviewee: Maria Martinón-Torres

So, this was excavated at the lab for more than one year, and we were progressively witnessing a surprise that what we were having in this sediment block was the partial skeleton of a child of about 2.5 or 3 years of age in exactly the same position almost as it was laid 78,000 years ago. So, this was like the beginning of a big surprise that made us try to understand, using all of our knowledge from many different fields, we’re talking about palaeoanthropology, we’re talking about taphonomy, which is a bit like the CSI of our field in palaeontology, trying to reconstruct the sequence of events that led you to find a body in that exact position.

Interviewer: Adam Levy

The body had not moved from the position it was carefully laid in 78,000 years ago, and that suggested a deliberate act of burial, perhaps some kind of funeral behaviour. But establishing such extraordinary actions and motivations required extraordinary evidence.

Interviewee: Maria Martinón-Torres

We are talking about a type of symbolic behaviour. We are talking about thoughts, we are talking perhaps about feelings, which is a type of evidence that does not become a fossil, so we have to look for ways to try to trap that type of behaviour in our fossil archaeological record.

Interviewer: Adam Levy

Demonstrating that an act was a burial means showing three distinct actions – preparation of the site, placement of the body and covering the body up – and using a range of techniques, Maria and her collaborators were able to provide striking evidence for all three.

Interviewee: Maria Martinón-Torres

Someone really dug a cavity in the floor to place a body, and this has been covered and filled later with sediment from a different layer. This body has been placed in a very specific position that you usually find in other burials, but additionally we think that there may be some aspects that even point to a type of more careful or elaborate behaviour, which is the possibility that the upper part of the body was wrapped in a shroud and that probably the head was resting on a sort of material, something like a pillow of perishable material. So, in this case, we think that there is like an involvement beyond simply the position of a body in the treatment of this child.

Interviewer: Adam Levy

To archaeologist Louise Humphrey, who didn’t work on this study, it was clear the team went to great lengths to find evidence of this behaviour.

Interviewee: Louise Humphrey

I think certainly it was very thorough. It’s very unusual to find a burial in this time. The team were very fortunate in that respect and so undertook a very meticulous investigation.

Interviewer: Adam Levy

For Louise, the detail of the evidence – showing for example that the body decayed where it was placed and not before – makes clear that this was a deliberate funeral act.

Interviewee: Louise Humphrey

Unlike some other types of mortuary behaviour, there really is absolute indisputable evidence that there was an intention here to bury the individual.

Interviewer: Adam Levy

Now, there is evidence of burial in other parts of the world at much earlier dates, in both Homo sapiens and Neanderthals, but at 78,000 years old, this marks the earliest clear evidence of these behaviours in Africa, in an era termed the ‘Middle Stone Age’.

Interviewee: Louise Humphrey

The Middle Stone Age in Africa is associated with many different types of evidence for a more complex way of interacting with the world, and we see it in the technology and we see it in the symbolic objects, and I think that burials such as this can be seen as another manifestation of that more complex behaviour.

Interviewer: Adam Levy

So, the evidence reveals the meticulous and deliberate burial of a young child 78,000 years ago, but why? What were the motivations of the people who did this, other than the obvious practical reasons for disposing of a corpse to avoid contaminating a space or attracting predators?

Interviewee: Louise Humphrey

Within the human archaeological record, I think the motivations are nearly always going to be beyond that, and I think one of the most intangible aspects of mortuary behaviour does relate to the expression of personal loss. I think we can see that here in this burial because the body has been carefully placed. Those who undertook the burial made an effort to support the head of the child within the position that they wanted to obtain for the body. I think that reflects the level of care.

Interviewer: Adam Levy

This insight into how our own species treated the dead in the Middle Stone Age helps scientists understand the origins of our behaviour. But for Maria, unearthing this moment of human history has also been a deeply human process.

Interviewee: Maria Martinón-Torres

I think this is one of the most exciting discoveries I’ve ever been involved in, I would say from a professional and a personal level. With these types of studies you can see the roots of the features you identify yourself with. I think it really makes you connect with human nature. This need to prolong the existence of the people we love beyond death, and this mixture of really facing the human part of it, a child that was missed, a child that was cared for, a child that provoked a behaviour, probably a pain, far away from a community, really was able of touching, I would say, my brain and my heart. You really see all the human dimensions of something that goes beyond a scientific finding.

Host: Benjamin Thompson

That was Maria Martinón-Torres from the National Research Centre on Human Evolution in Burgos, Spain. You also heard from Louise Humphrey from the National History Museum in the UK. To read more about the discovery, check the show notes for a link to the paper and a News and Views article. Coming up in the show, we’ll be hearing about a new rechargeable battery that doesn’t contain any metal and can be degraded on demand. Before we get to that, though, I need your help. Our three-part mini-series ‘Stick to the Science’ – about science’s relationship with politics – has been shortlisted for a Webby, and we’re in with a shot of winning a People’s Voice Award. If you can spare a couple of minutes to cast your vote for us, that would be amazing. Voting closes on Thursday at midnight PST, so you don’t have too much time, but I’ll put a link in this week’s show notes where you can do so, and I’ll also put a link in where you can listen to ‘Stick to the Science’. Anyway, back to this week’s podcast. Right now, it’s time for the Research Highlights, read by Dan Fox.

[Jingle]

Dan Fox

July last year brought a record-breaking number of typhoons to the Western North Pacific: none, the first time such an absence has been seen in 55 years of record-keeping. Researchers analysed oceanic and atmospheric data in search of an explanation for the calmer-than-normal skies. They found that surface temperatures in the Indian Ocean in July 2020 were the highest on record, leading to a high-pressure atmospheric system that supressed typhoon formation. Anomalous ocean temperatures in the Atlantic and Pacific Oceans also contributed. Because climate change is warming the Indian Ocean faster than other tropical waters, the authors say this lack of typhoons might become more common in future. Read that paper for yourself in Geophysical Research Letters.

[Jingle]

Dan Fox

The world’s northernmost bird – the Svalbard ptarmigan – always knows when to breed, despite passing deepest winter in perpetual darkness and high summer bathed in 24-hour sunlight. Most birds have an inner clock that prompts them to perform specific tasks at specific times of day, but in summer, Svalbard ptarmigan live under a midnight sun and their activity during a 24-hour period doesn’t follow a consistent pattern. Nevertheless, researchers found that key genes for establishing 24-hour rhythms are active in the brain of the ptarmigan, which uses this daily circadian clock to time seasonal events. In birds kept constantly in the light, genes linked to reproduction became active, and the birds increased their activity in preparation for mating. The researchers’ experiments suggest that 14 hours after sunrise, the birds’ internal clocks check whether the Sun is still up. Check your internal clock to see if you have time to read that research in full in Current Biology.

[Jingle]

Interviewer: Benjamin Thompson

Rechargeable lithium-ion batteries are everywhere. Looking around my little corner of the South London basement that doubles as my studio, I reckon I can see maybe eight or nine of them powering different devices. They are an amazing technology, but not without their issues. Levels of recycling for lithium-ion batteries are low, for example, and there are significant socio-political, environmental and human rights concerns surrounding the mining of the metals they contain. As a result, lots of researchers are looking for alternative ways to create rechargeable batteries. Among them is Jodie Lutkenhaus from Texas A&M University in the US. Jodie and her colleagues have developed a metal-free rechargeable battery that can be degraded on demand, which they say could offer significant advantages in the future. I gave Jodie a call to find out more, and she gave me a quick chemistry lesson.

Interviewee: Jodie Lutkenhaus

Lithium-ion batteries work by shuttling lithium ions around internally, and for every lithium ion that moves, an electron moves, and the electron is what generates the current. Today’s lithium-ion batteries consist of a metal oxide cathode, a graphite anode and a liquid electrolyte that contains a lithium salt. And what we did was we replaced every component with a material that is metal-free and organic. So, the cathode contains a polypeptide that has groups hanging off that can undergo reduction and oxidation, and the anode contains a similar molecule that has a slightly different group that can also undergo reduction and oxidation. And we’ve replaced the lithium-containing electrolyte with an electrolyte that contains organic salts. And in that way, we store energy by exchanging organic anions instead of lithium cations. So, for every organic anion that moves, we’re moving around an electron and powering your device.

Interviewer: Benjamin Thompson

So, you say polypeptide there, Jodie, and of course, my background as a biologist, polypeptide to me means protein. So, in a way, are these semi-protein-derived batteries?

Interviewee: Jodie Lutkenhaus

Yeah, they’re inspired by proteins. So, proteins in your body contain many different arrangements of amino acids. What we’ve done is we’ve taken one of those amino acids and linked them up into chains, so we call it a polypeptide, and we’ve hacked it by adding on groups that can exchange the charge.

Interviewer: Benjamin Thompson

Well, one of the things in your paper that you put forward is that you can get these batteries to degrade, and I think lithium-ion batteries, they’re difficult to break down or to recycle, but these ones, you’re able to degrade them to potentially their base components on command. How does that work?

Interviewee: Jodie Lutkenhaus

It’s not too complicated. So, what we would do is take the materials and add some acid, and the acid is going to break down the polymer into its starting materials, such as glutamic acid, which is an amino acid. The key is finding the right concentration of that acid and the right temperature because it doesn’t happen under simple conditions. That’s part of why we can get the polypeptide to work in the first place because it’s stable enough in normal conditions and then we have to go to a slightly extreme environment to break it down.

Interviewer: Benjamin Thompson

And so, when you bathe these batteries in acid and raise the temperature and break them down to their component parts, can you then put them back together again and get another battery ready to go?

Interviewee: Jodie Lutkenhaus

Oh my gosh, that is my fantasy. So, my dream is to collect these materials and repolymerise them, reconstitute them into their original starting materials and do this forever, and that would a be a truly circular battery economy. The challenge to that is separation. So, once we degrade the battery, we have to separate every little chemical species, and separation looks like it’s going to be the biggest challenge for organic batteries in general. If it takes more energy to reconstitute and recycle the battery, what have you really accomplished?

Interviewer: Benjamin Thompson

I mean, it seems like there’s been a lot of people attempting to try and make batteries with no metals in them. How difficult was this to actually do?

Interviewee: Jodie Lutkenhaus

Accomplishing this was incredibly difficult. Many people before us have tried to create metal-free organic batteries, but none had been able to make them degrade on command in the way that we have. The big challenge is that when you want to make a material degrade on command, that also means it’s a little unstable, so how do you get a material to operate with robustness while at the same time stay stable and then degrade when you want it to? Because if something wants to degrade, it will degrade. That was the big challenge, and that’s where that peptide backbone becomes really important.

Interviewer: Benjamin Thompson

Well, if we can talk about the battery then that you’ve made, I mean how does it compare, how does it stack up, I suppose, to maybe one of the sort of AA lithium-ion batteries I’ve got sort of sitting on the table here beside me?

Interviewee: Jodie Lutkenhaus

To be honest with you, the performance of the organic polypeptide battery is not great. So, right now, it can deliver about one tenth of the capacity or the energy of the lithium-ion battery that you use today. So, there’s a lot of room for improvement. The main issue is that the materials over time, they don’t degrade but they dissolve. So, if your battery dissolves as your using it, its performance will fade, and there’s some pretty easy fixes for that, so I still feel optimistic that this performance can be improved with further research.

Interviewer: Benjamin Thompson

Battery technology is big business, right? I mean, there’s a variety of different avenues being followed and different technologies that are being advanced that last longer or give more power or this or that. What is it about yours that you would say that makes it warrant this extra work because at the moment you are one out of a sea of other technologies.

Interviewee: Jodie Lutkenhaus

Yeah, I think the two things that really stand out about this work is that it’s metal-free, so it addresses global materials supply and demand and also socio-political issues with how those materials are obtained. And then it offers the hope of fully recycling a battery so that you never have to go into a mine again.

Interviewer: Benjamin Thompson

How long, Jodie, do you think until I can maybe look around where I’m sitting now and rather than seeing lithium-ion batteries I might be able to see your polymer-based batteries instead?

Interviewee: Jodie Lutkenhaus

Well, I think in general for the field, for a polymer-based battery, I think it could be five years because there’s so many people working on them doing fantastic work. For a degradable battery, it will probably be five to ten years because keeping the materials stable requires a bit more effort.

Interviewer: Benjamin Thompson

That was Jodie Lutkenhaus there. You can find a link to the research paper she and her colleagues have written about the new battery over in the show notes. And that’s all for this week’s show. Before I go, just time once again to ask you to cast your vote for us in the Webby Awards, and why don’t you tweet us – @NaturePocast – or email send us an email on podcast@nature.com to let us know that you’ve done so. I’ve been Benjamin Thompson. Thanks for listening. See you next time.

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