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Interviewer: Benjamin Thompson
Welcome back to the Nature Podcast. This week we’ll be learning what ancient houses can tell us about in inequality.
Interviewer: Adam Levy
And we’ll also be taking a look at a bacterial communication system. This is the Nature Podcastfor November the 16th 2017. I’m Adam Levy.
Interviewer: Benjamin Thompson
And I’m Benjamin Thompson.
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Interviewer: Adam Levy
First up today we’ve got a bit of an unusual topic for the Nature Podcast. We spotted a paper in this week’s issue about how inequality in a society, could have something to do with whether that society has cows. Shamini Bundell has been finding out more.
Interviewer: Shamini Bundell
Economic inequality and the wealth gap sound like very modern topics. Are the rich getting richer and the poor poorer. Tim Kohler is interested in how patterns of wealth change, in particular this gap between rich and poor but he’s not looking at modern societies. Instead, he’s using archaeology to figure out the economic inequalities in prehistoric human societies but if the societies have no written records, how can you find out how rich or poor the people were?
Interviewee: Tim Kohler
The way we can tell about wealth from the archaeological record is always indirect because we don’t have tax returns for example or any of those nice things. What we do have are house sizes, so, cross-culturally it seems to be true that richer households live in larger houses.
Interviewer: Shamini Bundell
And so that allows you to see, okay, over here we have… all the houses are kind of roughly the same size whereas in this one most of them are small but there’s a big castle in the middle. Maybe someone super rich lived there and ruled over all the rest or something like that?
Interviewee: Tim Kohler
That’s exactly the line of evidence we’re using and of course if you have things on those extremes, it’s easy enough for archaeologists to spot that. But in many cases the distribution is someplace in the middle. You might have quite a few small houses and some somewhat larger houses. And then one can construct what we call a Gini coefficient which is a measure of the unevenness of the distribution of house sizes. So Gini coefficience will be high, that is, towards one when a few households control most of the wealth in a society and they’ll be quite low, towards zero, when wealth is evenly distributed.
Interviewer: Shamini Bundell
How unequal are different societies around the world today?
Interviewee: Tim Kohler
Well the developed countries, they tend to run anywhere from about, say, 0.45 up to about 0.8 or 0.85 with the United States.
Interviewer: Shamini Bundell
So, going back through history, is the wealth gap something that has been changing through different civilisations?
Interviewee: Tim Kohler
In hunter gatherer times, that is, before the last 10,000 years, wealth distributions were probably very narrow, but then as people began to develop domestication of plants and animals, rather slowly at first, Ginis begin to creep up and they really start to take off when people become very sedentary and then they can efficiently pass material wealth along including land, including cattle, including material goods of all sorts to their children and then it can accumulate and things get much less equal.
Interviewer: Shamini Bundell
So you went all through history, you took archaeological sites from all over Eurasia to China, Europe and a bunch from North America as well. Were there any surprises when you actually started looking at the data?
Interviewee: Tim Kohler
At first when I looked at the data, I thought well, it’s about what we expected to see but I got my big surprise when I looked at the Gini trajectories at the largest possible spatial scale. That is, I divided the world up into the old world, which is primarily in our sample Eurasia, and the new world which in our sample is North America and Mesoamerica, which is to say Mexico.
Interviewer: Shamini Bundell
So you were looking at before the Europeans arrived?
Interviewee: Tim Kohler
Yes in the period we call pre-Hispanic, before Columbus gets here and what stood out was that in the first 2500 years or so, after societies developed agriculture, their increase in Gini trajectories was very similar. But the big surprise was that at about 2500 years after agriculture and been developed in any specific location in either the old world or the new world, the Ginis in the old world continued to increase in magnitude whereas the Ginis in the new world stayed about the same and continued at about the same level throughout the rest of the prehistoric period. They never got up the levels of inequality that we see in the old world and so that became the big puzzle. Why is it that the old world and the new world diverged at that time?
Interviewer: Shamini Bundell
So when I think about early farmers who are first starting to settle and domesticate crops and things, I can’t see any obvious differences between North America and the old world, so what on earth is creating such a different pattern in how their societies evolve?
Interviewee: Tim Kohler
What happens in the old world, we believe, and this is at the level of a hypothesis at this point is that agricultural extensification begins to be important. Extensification means that people are beginning to use draught animals, oxen for example, to be able to farm large areas that aren’t necessarily very close to where they’re living and probably only certain households can afford to keep a big healthy team of oxen and those households can rent out their teams of oxen to other households so that’s a real difference and I think that in part it’s made possible by large ‘domesticable’ mammals like cattle.
Interviewer: Shamini Bundell
So I can understand that the Europeans and Asians are using oxen like this but surely there must be some equivalent in North America where they could have done the same.
Interviewee: Tim Kohler
Well not really. The closest parallel there was was in South America where there were camelids, llamas and alpacas, but these animals were too slight to be able to pull a plough. And then if you look at North America and Mesoamerica there were simply no large ‘domesticable’ animals.
Interviewer: Shamini Bundell
It seems really simple to pin this whole evolution of wealth disparity on sort of, hey, I’ve got some oxen, now I’ve got cows; my problems are over. Do you think it really is that simple?
Interviewee: Tim Kohler
No it’s not that simple and we don’t mean to claim it’s that simple but we do look to try and find this original difference that began to snowball into creating other differences.
Interviewer: Adam Levy
That was Tim Kohler at the Washington State University talking to Shamini Bundell. His paper is out now at nature.com/nature along with a News and Views article.
Interviewer: Benjamin Thompson
The News Chat is still to come, where we’ll be learning about ‘Eve’ the research mouse and her countless descendants. First though, Shamini’s back and she’s brought the Research Highlights with her.
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Interviewer: Shamini Bundell
Scientists have discovered that male fringe lipped bats furnish their forearms with an odorous crust for reasons that aren’t entirely clear. This crusty cologne was found on bats all year round but the number of smelly males captured increased from September to December, just prior to the female bat’s peak pregnancy time in March. Males with these forearm crusts also had enlarged testes, adding further weight to the theory that this dressing up has a role in reproduction. The chemical composition of the acutely smelling accoutrement is currently unknown although the researchers suggests it’s unlikely to be secreted but potentially could be related to the bats’ saliva as crusty males were shown to lick their forearms more. Fly on over to the Journal of Mammologyto read more.
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Interviewer: Shamini Bundell
Researchers in the US have been using x-rays to examine explosions in encased spaces like rocket casings. They used high-resolution x-rays to probe the ignition of small aluminum canisters packed with one of two explosives: TATB or HMX. When heated to ignition, the group noticed a difference between the two combustible compounds. TATB’s big bang is largely down to heat conduction. HMX’s accelerated explosion on the other hand is caused by a combination of conduction and convection of hot gas. It’s hoped that this new knowledge will enable explosion rates to be manipulated in the future. Blast off to Applied Physics Letters to read the whole paper.
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Interviewer: Benjamin Thompson
Right, my slot now, and today I want to talk about communication. Not communication between humans. Not even between animals. Today I want to talk about bacteria and how some of them ‘speak’ to each other, through a process known as ‘quorum sensing’. So let’s talk about how it works. The system is controlled by a small diffusible signalling molecule the quorum bacteria release into their environment. When there’s just one bacterium present not much happens as the signal is too diffuse to do anything, but as this bacteria multiplies into a colony and all the members are released in the signalling molecule, it gets more and more concentrated. Eventually the molecule reaches a threshold and boom it binds with its corresponding receptor and switches on a set of specific genes. Now this happens in all the bacteria and it pretty much happens in unison. Quorum sensing was first discovered in the late sixties, early seventies but for a couple of decades there wasn’t much interest in the field and far from a quorum of researchers working on it. One of those researchers though is Pete Greenberg from the University of Washington who’s co-written a review for Natureabout the history and future of quorum sensing. Interest in the topic picked up again in the 90s after some important discoveries, as Pete explains.
Interviewee: Peter Greenburg
A group from Rochester discovered a system in a human pathogen, pseudomonas aeruginosa. I think finding a human pathogen that used quorum sensing to control its virulence really changed the trajectory of how the field was expanding.
Interviewer: Benjamin Thompson
Pseudomonas aeruginosais a bacterial species that can cause disease in animals, plants and humans. While other bacteria use quorum sensing to control things like luminescence, in pseudomonasit controls some rather different genes.
Interviewee: Peter Greenburg
Inpseudomonas aeruginosa, our pathogen, it turns on genes for production of an extracellular protease, production of toxins – pseudomonas make cyanide – and other factors that we call public goods: things that are outside the cell and can be shared by all the members of the group
Interviewer: Benjamin Thompson
So this isn’t the Naturepolitical science podcast but this talk of public goods and sharing implies that an element of socialism is involved in quorum sensing. The bacteria all work towards a common goal, helping each other out and sharing the rewards. However, given that it takes energy to be part of the team, there can be the temptation to not play by the rules.
Interviewee: Peter Greenburg
The concept really surrounds what I call Darwin’s Dilemma. Other people have called it that too and that is that there is some cause to cooperate and produce shared resources. If a cheat is among us, a cheat will have a fitness advantage because it won’t pay the cost of cooperation but can benefit from the cooperation of others and if it has a fitness advantage it should overtake the population, yet we know cooperation exists.
Interviewer: Benjamin Thompson
To learn more about cheating researchers grew pseudomonas aeruginosaon milk protein. The bacteria secrete an enzyme to break down this protein which allows it to be used as food. Enzyme production is under the control of quorum sensing so it only gets switched on when the colony is of sufficient size. But in this population cheats emerge who have lost their quorum sensing machinery. These mutants don’t have to waste energy secreting enzymes. They just freeload off the work of their colony mates. If too many cheats emerge, there’s not enough bacteria doing the work and the colony collapses. Under these conditions levels of cheating pseudomonas fluctuateat around 30% of the colony. Pete and his colleagues have identified one of the ways that the productive members keep the cheats in check. This process is called policing.
Interviewee: Peter Greenburg
And the way these bacteria do this is they make toxins that the cheats can’t make. They couple toxin production to quorum sensing so if you’re a quorum sensing mutant you don’t make the toxin, turns out you don’t make the immunity factor for the toxin. The cooperators make the toxin, deliver it to the cheats and it holds the cheats at bay.
Interviewer: Benjamin Thompson
So things in our bacterial utopia have taken a bit of a dark turn here. Not only do cheats exist but if you’re caught freeloading there’s the chance that you might be killed by your more industrious neighbours. And it’s not just the cheats within that you might need to be careful of in your quorum sensing colony. Another area being researched is the threat of spies listening in.
Interviewee: Peter Greenburg
So there are bacteria that have signal receptors and don’t have genes to make the signal themselves. Salmonella was the first example that was discovered and the idea is that they’re eavesdropping on populations of other species and somehow that eavesdropping is giving them a fitness advantage.
Interviewer: Benjamin Thompson
Despite being discovered almost 50 years ago, there’s still lots to learn about quorum sensing. There’s hope that we can manipulate the system, for example, to mitigate the ability of bacteria to cause disease. As someone who’s been studying these systems for years, I asked Pete what the big concepts are that we still need to get a handle on.
Interviewee: Peter Greenburg
In the review we talked about the next field which was understanding how groups of bacteria can interact with one another. For a human analogy, and these are always dangerous, we’ve learned how individuals within a city are interacting with each other. But we know that two cities next to each other can interact on some higher level way. We know that bacteria exist in clusters and groups. We don’t know how those groups interact with each other.
Interviewer: Benjamin Thompson
That was Pete Greenburg from the University of Washington there. Head over to Nature.com/Nature to read the review which covers lots of different aspects of quorum sensing.
Interviewer: Adam Levy
Time now for this week’s News Chat, and I’m joined in the studio by Lizzie Gibney, senior reporter for the physical sciences here at Nature. Hi Lizzie.
Interviewee: Lizzie Gibney
Hi Adam.
Interviewer: Adam Levy
Now, first up, a story that’s probably quite close to your heart. It’s particle physics story and there are plans to build a particle accelerator. Firstly, what’s wrong with the LHC?
Interviewee: Lizzie Gibney
The LHC is great but at some point we are going to want to move on to something that will be a follow up. So you could have greater energies that you could collide particles together with or you might have a different type of machine that collides different types of particles. So physicists are looking to the future, to say, 2030 and beyond to when we’ve used the LHC for everything we can use it for and we need something else.
Interviewer: Adam Levy
So in this specific case it’s to do something a bit different to what the LHC does.
Interviewee: Lizzie Gibney
Exactly, so it will still be colliding particles but instead of being a massive ring that collides protons which contain quarks, this would be a linear collider and it will be smashing together electrons and positrons, so that’s the antimatter version of electrons. So it’s a much cleaner kind of collision and you’d be making much more precise studies. Japan actually pitched, effectively, to host this facility which is known as the ILC, the International Linear Collider in 2012, just after the discovery of the Higgs Boson.
Interviewer: Adam Levy
So that’s the plan for this collider but as I understand that plan’s been somewhat scaled back lately.
Interviewee: Lizzie Gibney
That’s right, so for decades now, for 25-30 years maybe this collider has been on the table as the most likely follow up to the LHC but of course throughout that whole period most people expected that the LHC would be finding more particles. Obviously it very famously found the Higgs Boson that endows other particles with mass in 2012 but since then it hasn’t found anything else despite working amazingly well. So the question is how much do we need a new collider and what exactly should it be looking for? So the plan was always to build around a 30 kilometre linear collider and go up to energies of around 500 giga-electron volts and now what physicists are talking about is a plan to just reign that in because it’s very expensive. It’s going to be about 10 billion dollars. And the thing is at the moment we don’t actually know that it would be exploring any new particles because we haven’t found any. So the proposal is to make it a little bit cheaper which might make it a bit more palatable although to be honest it’s still probably going to be quite a hard sell. But in doing that you would also have a slightly different physics case. So you’d still be able to study the Higgs but you would no longer be able to study the top quark which is the heaviest quark particle.
Interviewer: Adam Levy
If it’s scaled back in this way and it’s only really designed to be studying the Higgs, is it still worth doing?
Interviewee: Lizzie Gibney
Physicists would say yes, of course. The Higgs Boson was discovered really very recently and it’s only been studied at the LHC so there is a very strong case for doing it. Undoubtedly the case would be much stronger if we had whole new particles that we were probing.
Interviewer: Adam Levy
Our second story today is a UK science policy story and the UK has a new science advisor.
Interviewee: Lizzie Gibney
Yes, so we have a bunch of science advisors. This is the government’s chief scientific advisor. So this is the person who gives science advice to the Prime Minister and to the cabinet, so the most senior decision making body and generally ensures as much as possible that government is making good use of science and of evidence.
Interviewer: Adam Levy
And who are they?
Interviewee: Lizzie Gibney
So this is a person called Patrick Vallance. So he has come from GlaxoSmithKline, so from the pharmaceutical industry. He did have a career in universities before that so he’s not purely from the industrial sector because I’m sure that would rile some University scientists. And yes, he’ll be starting in April next year.
Interviewer: Adam Levy
Always a very important role for looking at what’s happening in science and research across the UK. But of course right now it’s especially important.
Interviewee: Lizzie Gibney
Absolutely, so at the moment there’s this funny little thing called Brexit and it’s an enormous undertaking for the government. A huge number of regulations and laws are going to have to be rewritten and a lot of these touch upon science policy, whether that be in the nuclear industry, and then there are also very many environmental laws and generally it’s across the board that there are impacts on science and there are places where we need really good evidence informing what the UK should do when it rewrites these laws and regulations. So it definitely seems to be the case that the role of scientific advisor in this way is going to be even more important than ever.
Interviewer: Adam Levy
Considering all that’s going on, what’s the opinion of Patrick Vallance? What’s the response to his appointment?
Interviewee: Lizzie Gibney
The response is pretty good. He’s a little bit of an unknown quantity, perhaps because he does come from industry so nobody really knows whether he’s going to have any big passion projects so I think people will be looking at what he does first with great interest.
Interviewer: Adam Levy
Let’s move on to our third and final story for this week and it’s a story of one very special mouse called Eve. Why is Eve so special?
Interviewee: Lizzie Gibney
So Eve is a mouse who was born at the Jackson laboratory in the states and she and her partner Adam are the parents of a huge number of mice who are of a very popular strain who are used in biomedical research and Eve is a lucky mouse in that she’s getting her genome reconstructed.
Interviewer: Adam Levy
I have to say I’m a little offended that they chose to reconstruct the genome of Eve and not Adam but putting that aside for the moment, why are they interested in Eve’s genome?
Interviewee: Lizzie Gibney
So generally when you’re using mice in biomedical research you want to keep them as genetically similar as possible but of course if you use subsequent generations there are going to be mutations and every generation about somewhere between 10 and 30 new mutations pop up and they keep being passed down and they call that genetic drift. Now, the point is when you have these changes they can have physiological effects that actually affect experiments so they’ve shown that, for instance, some sub strains of this popular strain of mice have very different tastes in alcohol. Some have quite different immune system responses and of course that can really affect the experiments that you’re doing. So what they’re trying to do here is to construct the genome of Eve so they have something that they can compare their strains to. Then you can figure out what the differences are with the strain you’re using and you can compensate for them.
Interviewer: Adam Levy
So does this then fix a problem for all lab mice that we have or is it just some kind of specific set?
Interviewee: Lizzie Gibney
This is a specific set. So Adam and Eve were mice who lived at this lab in 2005 and the researchers there realised the potential for this problem of genetic drift and so they froze dozens, or hundreds even, of the embryos of the grandchildren of these mice and every five years they restart the strain but you’re always going to get this drift. So that lab has come up with a particular way of not solving but slowing the problem, but of course different strains at different labs developed by different firms will have genetic drift in different ways.
Interviewer: Adam Levy
Well even so, good for all those labs that are using the descendants of Eve in their experiments. But how good is it? How big a difference is genetic drift having?
Interviewee: Lizzie Gibney
So, it’s really hard to actually figure out exactly what kind of an impact it’s having. Probably a significant one but the awareness is pretty low within labs how much drift they might have in their mice and how much they probably do need to compensate for it. So it might be that experiments or entire research programmes are wasted when people think they’re using identical mice and actually they are genetically diverged. But at the moment we don’t know.
Interviewer: Adam Levy
Lizzie, thanks for the update. For more on those three news stories head to nature.com/news
Interviewer: Benjamin Thompson
So that’s it for this week. Thanks as always for listening. Don’t forget to follow the show on Twitter. We’re @NaturePodcast, and you can contact us via email: podcast@nature.com. I’m Benjamin Thompson
Interviewer: Adam Levy
And I’m Adam Levy. See you next time.
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