GM mosquitoes fight malaria, and robot digit gets thumbs up

Plus, the cuckoos in an evolutionary arms race
31 May 2024
Presented by Chris Smith
Production by Rhys James.

OXITEC MOSQUITO RELEASE.jpeg

Oxitec mosquito release

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This episode of The Naked Scientists: The genetically engineered mosquitoes released to fight malaria in Africa; how fake news skews public opinion, and who is behind it; and, finding out what it’s like to own an extra thumb!

In this episode

Oxitec mosquito lab

Genetically modified mosquitoes to fight malaria
Grey Frandsen, Oxitec

Genetically engineered mosquitoes are taking to the air in an experiment to attempt to curtail malaria in Djibouti. The tiny African nation all but eliminated malaria just over a decade ago. But rising population and urbanisation has seen disease cases skyrocketing again, making it an ideal venue to test the technology, which uses a genetic trick to kill off selectively female mosquitoes; this leaves the males - which don’t bite humans - unharmed to breed and pass on the trait to other members of the species. Oxitec’s CEO is Grey Frandsen…

Grey - We are the pioneers in using genetics to engineer good mosquitoes. And these are non biting male mosquitoes. When released, they seek out and mate with wild type female mosquitoes and all female progeny, all the female babies of that mating will die. And over a successive number of releases of our good mosquitoes into the environment, we will see a dramatic suppression of those malaria transmitting mosquitoes. And we're now bringing that technology, that approach, to the fight against malaria precisely because all of the tools that we have used to date have begun to lose effectiveness. Mosquitoes have engineered themselves around all of our existing tools or weapons to fight these mosquitoes. And thus we are in a race against time to save lives.

Chris - I think they call this a gene drive, don't they? It's one of the ways it's referred to. How do you make that happen?

Grey - So in this case, in Africa, there's a spreading malaria transmitting mosquito called Anopheles stevensi. This particular mosquito is spreading very rapidly in urban settings, in cities where millions of people live. Most malaria cases to date have been transmitted in rural areas, rural Africa for example. We introduce two genes into the genome. One is a fluorescent marker just so we can see under a certain microscope where our mosquitoes are. But the magical gene is one that in essence allows us to release only males, and that kills all female progeny, therefore rapidly reducing the population. It's targeted, it's specific, and has no impact on any other part of the environment or the ecosystem.

Chris - How does it kill the females selectively?

Grey - The team we have, just outside of the Oxford area, have pioneered the ability to create, in essence, an on and off switch inside the genome of a particular targeted mosquito. What that on and off switch allows us to do, in essence, is manufacture mosquitoes at scale, which requires us to keep females alive so we can create lots of male mosquitoes. And then when we release those mosquitoes outside of our factory or outside of the lab, and in the absence of a certain antidote, the kill switch in essence turns on and the kill switch only turns on and interrupts cell production machinery in female mosquitoes.

Chris - And why have you gone for Djibouti to test this? Apart from the fact that levels of this disease are rife there again and they're going up so it makes it a good target from that point of view. But why specifically Djibouti? There are lots of places where malaria is active.

Grey - Indeed. So Djibouti is at the perfect and troubling intersection of climate change, of rapid urbanisation, of increased transportation between countries. And when you add all of those things together, it creates a perfect environment for this malaria mosquito that is spreading very rapidly in these urban environments. So Anopheles stephensi has, in essence, invaded Djibouti and has had a deadly impact. They went from near elimination in 2012, 13 to now tens and tens and tens of thousands of malaria cases spread by this particular mosquito. Now, in 2018, Djibouti's public health leadership reached out to our team and asked if we would develop a new mosquito, a new Anopheles stephensi Oxitec friendly mosquito to help them. And that is a request we could not deny. We had to lean into this and help them solve this problem. And frankly, it's not just a Djiboutian problem. This invasive mosquito now has spread across the African continent and continues to enter into densely populated urban environments.

Chris - Presumably you've modelled how you expect this to play out as the mosquitoes spread and they carry this kill switch into the females and slowly suppress the population. You must have a sort of trajectory in mind as to what you're expecting to see. So how will you monitor that?

Grey - Great question. So the trajectory we hope to see does start in Djibouti. We're basically comparing where we released ours to an area where we didn't release ours, and we will see significant suppression in the area we've treated. Beyond that, we begin scaling up, we demonstrate the effectiveness of the mosquito solution in successively larger environments, and then we begin preparing to scale it for interventions where an Oxitec mosquito plays a direct role in a government's efforts to control this particular vector. Then we begin spreading across the African continent to treat those cities where governments wish to see us deployed.

Chris - What's the end point for this? Because there must be a law of vanishing returns applying here where you end up, to drive it really down, you have to release so many of these mosquitoes to get to the last vestiges of the mosquitoes that are still breeding. And as soon as you take your foot back off that accelerator, does the whole thing not change direction and come roaring back?

Grey - Frankly, for this particular malaria transmitting mosquito, we see this as the primary method by which we will secure control over this mosquito. Now to your particular question, yes. Over time we will have been successful in knocking down maybe 90% of the population. That last 10% of the population requires fewer and fewer releases of Oxitec mosquitoes because we have fewer and fewer mosquitoes to target. And ultimately we would hope to create a significant suppression such that we drop that remaining wild type presence below a disease transmission threshold where it becomes either completely unimportant or not a threat to the civilian population.

Chris - What about the possibility given that the mosquitoes have just in our generation adapted and continue to do so? That will drive the evolution of wild type mosquitoes through doing this and will evolve a new generation of Anopheline mosquitoes that don't die when they get this genetic switch. And that means we'll end up with a really tooled up mosquito that <laugh> is gonna bypass your blockade.

Grey - It's a very good question and one that we are asked often, but the manner in which our technology works, it's a mating based, species specific, female focused solution. We will not see resistance to our particular gene technology. And that's good news. Unlike chemical pesticides or insecticidal properties or a bed net, for example. Those are blanket active ingredients or chemicals that are spread time after time, after time, giving mosquitoes a chance to generate resistance by way of mutations and normal selection processes. For ours, we are introducing male mosquitoes that will target only the targeted species. And again, all females die and thus there is no chance for selection on those grounds.

A cup of tea and laptop with YouTube on

Tiny number of supersharers cause 80% of web misinformation
Sander van der Linden, University of Cambridge

In recent years we’ve all become much more familiar with the threat posed by online misinformation. It can undermine confidence in health initiatives like vaccines, and skew public opinion around politics. Now two new papers published in the journal Science shed some light on how potent different sorts of misinformation are at influencing members of the public, and who is behind their creation. One notable observation to emerge from the research is that information that’s not wrong, but could be interpreted the “wrong way” by audiences is extremely powerful. To quote the summary written by the journal, “factual yet misleading vaccine content was 46 times more effective at driving vaccine hesitancy than flagged misinformation.” Sander van der Linden, from the University of Cambridge, works on how we’re affected by misinformation. He wrote an opinion piece alongside the new research this week…

Sander - So they wanted to see if A) what is the causal effect of being exposed to misleading information about vaccines on people's intention to get vaccinated? And B) how can you estimate the total damage from that? And can we estimate maybe even how many lives could have been saved if people hadn't been exposed to this type of misinformation?

Chris - What do we call misinformation though? Because I put it to you the Chicago Tribune, during all this, led with a headline that said a doctor died two weeks after having the Covid jab. But it doesn't go on to say, and that was because he was run over or he had a heart attack, which was nothing to do with the vaccine.

Sander - Exactly. That headline was one of the most viral headlines because millions and millions of people were exposed to it. And the exact question there is, a healthy doctor did die two weeks after getting the vaccine, right? But it falsely implies causation where there's only correlation. And that is a well-known logical fallacy. And so that's why it's misleading, even though the words technically are true. But what they wanted to do in this study is find out how persuasive are total falsehoods compared to these more subtly misleading statements. And what they found was that this misleading type of headline, true but misleading, was 46 times more damaging in a way than the effect of outright falsehoods on people's intentions to get the vaccine.

Chris - Why do you think that is?

Sander - Well, from a technical perspective, the answer is reach. So if you look at outright falsehoods, they're not shared by that many people. So their reach is fairly limited. So if you look at the maths in their papers, basically what they try to estimate is what's the percent reduction in your intention to get vaccinated? And then they need to multiply that by the actual exposure on social media. And so outright falsehoods have actually quite low exposure, whereas mainstream media that's highly misleading has huge exposure. And so when you combine the effects from persuasion in the lab with huge numbers of millions of people being exposed, that's where you do quite a lot of damage.

Chris - Is the take home then that more responsible reporting is needed? Because it sounds like that was just a shoddy headline that was clickbaity. Is that really what we're talking about here? That we just need more responsible journalism?

Sander - Yes, in a way, I think we do need more responsible journalism. And that means fewer clickbait headlines, fewer emotional manipulation, fewer articles that have a clear or biassed slant. But the other thing we need is maybe to broaden our understanding of what is misinformation. And so there's some consensus among experts that it shouldn't be just outright falsehoods because that's a fairly small proportion of what we see on a daily basis. The bigger problem is misleading content, right? There's some nugget of truth in there, but it's otherwise manipulative. And I think that is the bigger problem and the bigger part of the definition. So when we think about misinformation, we shouldn't only think of flat earthers, but also about mainstream content that is highly misleading.

Chris - And the other paper looks at something very relevant right now, both sides of the Atlantic, that's elections and election bias and spreading misinformation. They say a staggering amount, 80% plus, of the misinformation originated from a tiny fraction.

Sander - Yeah. And these are called super spreaders or super sharers. And that's a more general finding that we find that most of the fake news comes from a small group of highly networked, highly influential individuals supplying up to a quarter of the falsehoods that their followers see in their newsfeed. So if you are on Twitter, about a quarter of the falsehoods you might see might be coming from a super spreader or a super sharer that you're following, intentionally or on accident. I'm assuming nobody in the audience in your audience is following any super sharers, but if there were the case, that's basically what what they found. And now I will say that the difference with the other study is that they focus on outright fake news. So if you put two and two together, what we haven't looked at is who are the super sharers of misleading information. Because we know misleading information can be more impactful, but who are the super shares of generally misleading content? Because they're the ones exacerbating the reach. So you were basically coming back to the Chicago Tribune headline. That was actually influential amongst anti-vaccination activists as you predicted. It was a mainstream outlet that published it, but it was pushed by anti-vaccination groups on Facebook. Similarly, there was another study recently that showed that there's about 50 physicians in the US that were responsible for a huge amount, a disproportionate amount of Covid misinformation. So there's these networks of highly influential actors that are amplifying fake as well as misleading content. And in fact, if you look at the motives of super spreaders, they're quite diverse. For some it's fame, for others it's financial. And so to what extent we’re able to change their motives is an open question. Maybe it's more realistic to try to somehow intervene, to make sure that their followers are not exposed to it. Maybe that's a more plausible route than actually trying to change the super spreaders themselves.

Chris - So persuading the social network platforms themselves to do something. One person I spoke to, she did a study looking at whether you could add a button. Instead of just like and dislike, an 'I trust this' content. And then you are basically pinning your integrity to the message and people will be a bit more hesitant to pin their integrity on something that might be dubious rather than just like it and share it.

Sander - Exactly. And I think misleading content is especially problematic, aligns well with the research that we do, which is about helping people spot manipulation in content wherever they may see it. But I was going to say, we ran out of space, so the editors kicked out my final paragraph, which was about this newer study that shows that you can actually try to change the incentives too for super spreaders and their followers by implementing some sort of credibility metre. And so the idea is that if you keep floating untrustworthy content that's going to hurt a visible public credibility metre that might be assigned to you. And so nobody wants to put their reputation at stake if it actually means they're going to lose points, or they're gonna lose likes, or the audience might think that they're not credible. So assigning trustworthiness ratings to social media accounts could provide a different type of incentive. And I think it's not a bad idea.

Bronze Cuckoo

Crafty cuckoos in coevolution arms race
Rebecca Kilner, University of Cambridge

All life evolves; in other words, changes in response to selective pressures from the environment. And some examples of evolution are extremely complex because they involve two organisms evolving in tandem: one is a parasite and the other is its host. So what are the rules of engagement in this arms race? Cambridge University’s Rebecca Kilner studies cuckoos; and working with colleagues in Australia, she’s found that what began as efforts just to imitate the host bird’s eggs has morphed - down under - into full blown imitation of appearances and sounds of the chicks instead…

Rebecca - Our research focuses on how evolution works. And the way that we do that is to look at pairs of species where one species is exploiting another. So we're trying to understand how one species adapts to exploit another species and how that second species adapts to avoid being exploited. And we're interested in understanding whether there are general rules in how evolution plays out in those circumstances.

Chris - And the obvious example must be the cuckoo because this is a bird that plants its egg in another bird's nest and gets the parent birds to then bring up an offspring chick, which is not their own.

Rebecca - That's right. And that's hugely costly for the parent that's looking after the cuckoo chick. They pay the price for doing that. They lose their own offspring. The cuckoo chick kills their own young soon after it hatches by balancing any unhatched eggs or newly hatched chicks in the small of its back and walking up the side of the nest and tipping them out. So the host bird loses its own offspring and then it pays again because it works really hard to look after an enormous cookie chick that it has no genetic stake in at the cost of being able to breed again in the future. What we are interested in finding out is how those arms races play out. Do they always go in the same direction across evolutionary time?

Chris - How can you tell that?

Rebecca - Perhaps I could provide some kind of previous context to this. So the study of cuckoos and their hosts has been going on for some time and was initiated in Cambridge by professor Nick Davies some time ago. And he focused his work on the common cuckoo, and its many hosts in the UK. And what he showed was that the arms race is very much focused on the egg stage. So cuckoos lay their eggs in the host nest like a reed warbler. The reed warbler carefully scrutinises its eggs, and if it sees an egg that looks a little bit different from its own egg, then it picks it up and throws it out. And in that way it can avoid being exploited by the cuckoo. And that defence has in turn selected for cuckoos that can better hide their eggs in the nest. And so they lay an egg that closely matches the host egg in appearance. Where our work comes in is on a completely different set of cuckoos, which live in Australia. They're called the bronze cuckoos. They're quite small compared to the European cuckoo that we are familiar with. And what we showed there was that there was no equivalent arms race happening at the egg stage. The cuckoo lays an egg that's approximately similar to the host's own egg, but if we were to put a model egg in the nest that looked very different then the host wouldn't throw it out. And it turned out that what had happened was that the whole thing had shifted onto the chick stage. Unlike the UK cuckoo, the Australian cuckoo had evolved a set of rejection rules that were focused at the chick stage and involved spotting the odd chick in the nest. And they're able to do that by listening to the calls made by the cookie chick and also by observing that it was a single chick by itself in the nest, which seldom happened when they were raising their own young. And so this combination of cues would lead the female to dismantle the nest while the chick was still alive and begging in the nest and to build a brand new one. And then the cuckoo chick would slowly starve to death over the next couple of days. And then immediately after it died, the meat ants would come in and dismember the corpse and carry it off to their nest and feed their young with the bits of the body. And meanwhile, the host has started a new nest and a new breeding attempt.

Chris - How do you know what the timeline is here? How do you know that it started with egg discrimination, 'your egg looks different to my normal eggs. I'm going to chuck it out' versus the, your chick looks different to my chicks in Australia. Was it that that was first and the eggs came second? Or do you think they all started with egg discrimination and the Australian version has moved on to chicks? How do you know that's the timeline?

Rebecca - We don't know for certain because we haven't lived for the millions of years over which this arms race has played out. But we can deduce it from a few clues. And the first is that the egg that's laid by the Australian cuckoo looks unlike the eggs laid by its close relatives and much more like the eggs laid by its host. So something has happened at that stage. It may have been that in the past the host rejected eggs just as we see happening in European cuckoos today. What happens now, we suspect, is that the egg contributes to the decision to abandon the chick. So we did all these egg experiments where we put an odd looking egg in the nest and observed no immediate reaction from the host. But once we'd discovered chick rejection, we went back to those experiments and we noticed that chick rejection was more likely if we had added an odd looking egg to the nest for one of our earlier experiments. So what we think is perhaps the hosts remember this weird egg and then they use it as part of their accumulated information about what's going on with their current breeding attempt when there's a chick in the nest. And that informs their decision to reject or to continue to feed the chick.

Prosthetic thumb

23:35 - How does a person get to grips with an extra thumb?

Test subjects got to grips with their new digit with relative ease...

How does a person get to grips with an extra thumb?
Dani Clode and Lucy Dowdall, University of Cambridge

Most of us have, at one time or another, wished we had an extra thumb on hand to help with fiddly tasks. And Dani Clode, who designs limb prostheses, thought the same, so she made one! It’s basically a rubber robotic thumb that straps onto the bottom of the hand in roughly the opposite position to the native thumb, and closes up onto the palm or against the little finger. She wanted to know how people would get to grips with using an additional digit, particularly as we move into an era when body augmentations like exosuits that can help us to perform certain tasks, are set to become more commonplace. The result, which was showcased and tested on hundreds of members of the public at the Royal Society’s famous “summer science exhibition” also offers an opportunity to explore neurologically what happens as someone gains a body part and learns to use it. I went to meet Dani and her colleague Lucy Dowdall at the Cambridge MRC Cognition and Brain Sciences Unit to test it out for myself…

Dani - Cool. So, we're going to put a third thumb on you today. I do need you to take your shoes off, if that's okay.

Chris - Good job I put decent socks on.

Dani - <laugh>

Chris - It's not every day I turn up to an interview and someone says to get your shoes off <laugh>.

Dani - Yeah. You know, we do things differently here. <laugh>,

Chris - I thought this was for my hand. Why have I got to get the shoes off?

Dani - It's foot controlled. So each of your big toes is going to control one, what we call, degree of freedom of the third thumb, which is the two kinds of movements that it does. So one movement is across the hand and back and the other movement is kind of towards your fingers and back. And so your left and right toes are going to do that. So this is the device here. So there's a part that's worn on your upper arm, like on your bicep, and then that's connected to a wire. That's to the motors that are worn on your wrist. And then there's a hand piece that's kind of got two straps. That one goes between your thumb and index and then the other kind of around the base of your thumb. And that's going to keep the third thumb on your hand.

Chris - Okay. So do you need my sleeves rolled up or is this jumper friendly? <laugh>I mean I know this is The Naked Scientists, right, but there are limits <laugh>.

Dani - Yeah, we have to be jumper friendly in the UK don't we? <laugh>?

Chris - So this is going over my right arm. Yep. So it's on the forearm at the moment. You're going to put that further up here?

Dani - I've got to kind of shimmy it up your arm.

Chris - So the neck goes around. The hand is going over my fingers.

Dani - So thumb in. It goes on your wrist.

Chris - Right. So I now have a strap around my wrist. A strap around my hand and a thing, which looks like an exceedingly large thumb, but on the bottom, sticking out from the bottom of my hand. That's sort of, if I had monkey hands, that's the length of the sort of digit I would expect to have <laugh>.

Dani - Yeah. I made a smaller one, but it wasn't quite as functional. So, yeah, it's become bigger over the years. <laugh>.

Chris - So I now have, I presume that's a battery pack as well. Now on the back of my arm.

Dani - The battery pack and also the kind of PCB, the electronics that connect wirelessly to the foot control. And then I'm going to put two sensors underneath your big toes. You've got your left control here. If you press down, there we go.

Chris - Oh. Oh, okay. So this is, I press my left big toe down and I'm moving towards the rest of my fingers. My right toe, I'm moving my new thumb into the palm of my hand.

Dani - Yep. Yes. So you can see that the speed is responding quite instantly and wirelessly to the pressure of your big toes. I

Chris - Actually it's three degrees of movement, isn't it? Because I can go into the palm, I can go outwards in the direction my fingers are pointing if I was sort of pointing my fingers away from my body. But I can also move the device so that it's in any of the positions in those two directions. It's not just into the palm or out towards my fingers.

Dani - Yeah, I was tricky about that and actually got a bit for free in how the thumb is fully flexible. So it's 3D printed out of a flexible material. And so you are actively pulling in and then the flexible material is kind of pulling back out. So it kind of seems like there's a lot more degrees of freedom, but there's only two controls and two motors.

Chris - Do you reckon it'll hold a microphone? Shall I have a go? This is quite brave. It's quite heavy, this microphone. Okay, I'm going to have a go. It's quite strong.

Dani - <laugh> You want to go the other way around so you've got to change the way that you actually use your hand. So I would go that way. So push your right toe.

Chris - So you're putting the microphone along my hand? So it's gonna be grabbed. So let me just try that.

Dani - So right toe. And press and hold

Chris - You've got to hold quite tight. Yeah. <laugh>, but it has got it. I mean that's quite good. I'm not sure what I would do with it, because it's completely occupying the rest of my hand.

Dani - Yeah, it's a big microphone <laugh>, but what you're doing is you're freeing up the use of your fingers, especially your pinch grip for example, which is a super functional part of your hand. The third thumb can grasp something whilst then freeing up that part of your hand.

Chris - So what sorts of use cases would you see for this? I grant you, it's very easy to use this. It's my first go, I grabbed hold of something and I feel pretty confident that I can put this thing into any position relative to my hand. That's really easy to do. But what's the use case for this? What sort of applications do you foresee?

Dani - Yeah, well this kind of device is augmentation. So extending the function of the hand. It can kind of grasp an object whilst freeing up your kind of index or rest of your fingers. So for example, you know, holding a bottle whilst unscrewing the cap, that can be done one handed. So all these kinds of tasks that usually require two hands you can explore just using one hand.

Chris - So do you think surgeons might be interested in something like this? Because there are some aspects of surgery where surgeons say, I wish I was an octopus.

Dani - I would love to collaborate with surgeons on this. Especially people with professions where they are kind of hyper trained with their hands. You know, to then expand the function of a hyper trained hand surgeon is an interesting example because they use a lot of assistance. There's people that are perhaps having their eyes or other hands during the surgery and so to augment them and create more fluid function during surgery would be an incredible opportunity.

Chris - Lucy, you are the neuroscientist on the team. What's your role? What are you actually doing and trying to find out?

Lucy - So we're interested in how our experiences and our environment shape our brain. After five days of training with the thumb, we see changes in how our hand is represented in the brain and in our next steps in this research we're looking at how the third thumb itself is understood within this body representation. And that's really important. When thinking about if people are using these technologies in their everyday life, how is that then affecting our biological body?

Chris - When you say you see changes in the brain, what are those changes? How does the brain seem to incorporate it into its model of the body?

Lucy - In our brain we have a body representation. So for example, if I move any one of my individual fingers, I'll see an air of my brain devoted to that finger lighting up. And after five days of training, we find that after the training the fingers all become more similar to each other. So we're having a reduced representation of our hand in the brain. But we want to know is that because we're using our hand differently every day because we know that how we use our hand does affect how it's understood by the brain. Or is it something very specific to the third thumb itself and that being incorporated.

Chris - And if I put this on the other hand, which is obviously being controlled by the opposite side of my brain, if I put this on the other hand, does the learning transfer or do I have to start from scratch with the other side?

Lucy - So we're actually looking at this right now. We don't have the final data, but we are quite surprised to see it does seem to generalise very well. We've also looked at changing the controller, so moving from the toes to controlling it by the heels. And again, this learning seems to generalise. So there's something about this hand and foot coordination, people are able to learn very quickly and generalise very quickly.

Dani - With our current research that we were talking about as well, we actually found that we had a really inclusive range of people that tried the third thumb on for the first time at the Royal Society Summer Science Exhibition. And although it was only a right-handed thumb that I had, we included left-handers and right-handers and everyone had a very similar response to it.

Chris - That was why I was asking the question. Because I was thinking 90% of the population are right-handed. You've put this on my right hand. Yes. Did I find it easy because I am right-handed? If you'd given me a left-handed one, would I have struggled the same way a left-hander might if I gave them a right-handed one? Or does it just generalise?

Dani - It seems to just generalise, which <laugh> as the designer of it. I was quite surprised. I'm left-handed. So <laugh>, I use mine on my right hand. I dunno why I chose that, but it was probably so I could work on it at the same time. <laugh>.

Jumpstarting a car battery

Why do car batteries go flat?

Thanks to Rhod Jervis for the answer!

Will - Returning to a car after a few weeks or so can lead to a frustrating struggle as the only thing preventing the car from operating is one flat battery. But why does this happen? We put in a call to University College, London's Rhod Jervis

Rhod - There's a process called self discharge, which all batteries undergo to some extent. And then there is sort of the battery becoming flat, fully degraded and not possible to be regenerated. And that can unfortunately happen with lead acid batteries, which are the type of sort of starter batteries in internal combustion cars. So the process of self discharge is really one of fighting against the nature of all batteries. When we charge batteries up, what we're doing is putting them into a semi unstable state, thermodynamically speaking, and this is the equivalent of pumping water up a hill, up to a high reservoir. We're giving the battery that potential energy, but it also means it's in a state where it really wants to get rid of some of that energy. And in some cases that can lead to favouring some what we call side reactions that end up using a small percentage of the charge stored in a battery. So that happens in lead acid batteries, lithium ion batteries, lots of different types of batteries. Some of them lose their charge relatively quickly and have a shelf life of maybe a few, a few months. Others will lose just a couple of percent in a year or something like that. Most often it's reactions with the electrolyte. This is the sort of liquid in the batteries that carries the charged ions back and forth between the electrodes and then often that will use a very small percentage of the capacity. These side reactions, these self discharge reactions, are more likely to happen when the battery is in a high state of charge. And so leaving the battery very, very charged will accelerate those reactions as will increase temperature. So what we can do to avoid that is to maybe store the battery partially charged, not leave it in high states of charge for a long time, not overcharge it, not leave it in warm conditions, et cetera.

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