Emergency in Antarctica; How movement changes the brain; Why women live longer than men

0:00This episode is sponsored by Yakult, the gut experts for over 90 years. Antarctica is a lot warmer than it should be. Since the beginning of September, temperatures in the atmosphere above Antarctica have soared by over 35 degrees C. We have a report from a climate meeting this week about what that means. Also on the show today, we have a new explanation for why women typically live longer than men and indeed why in many mammals females live longer than males. And we're also going to be learning about how the human brain swivels to focus on sound from different directions and what that tells us about how our brain works better when we're on the move.

0:36That's coming up. I'm Dr Penny Sarche. And I'm Dr Rowan Hooper. Welcome to The World, The Universe and Us. And Penny, our show has been nominated for an award. It has, yeah. The World, The Universe and Us is up for Best Science Podcast in the Signal Listener's Choice Award. And that means we need as many votes as possible. So we are shamelessly appealing to you to vote for us. It's the Signal Listener's Choice Award in the science category. We'll put a link in the show notes. Do please vote. We really appreciate your support. We're going to start with Antarctica. At this time of year, the Antarctic atmospheric temperatures should normally be minus 55C, but since the 5th of September, they've risen to minus 20.

1:14That means wind speeds in the stratosphere, what they call the polar vortex, they've dropped by half and it's now only 100 kilometres an hour winds up there. Madeline Cuff is here to tell us about it. Maddy, you've just been at this conference on Antarctica. What was the mood like? Hi, guys. Yep, that's right. I've been at a conference on Antarctica in London that was organised by the Royal Society this week. And it's all about the latest scientific research coming from the polar continent. It's fair to say that scientists are pretty worried about how quickly things are changing there. They're always understated when they say they're worried, aren't they?

1:49Is that for the rest of us, it would be like total fear? Yeah, I think red alarms flashing. Yeah, red alarms flashing. It is an emergency in Antarctica. Let's start with the polar vortex, and that's what's been causing some weird weather and other conditions in Antarctica. And the vortex is this measure of wind speed in the stratosphere, and that traps, normally traps, really cold air above Antarctica. And if it slows down, that's when warmer air can get in, warmer weather can get in. Yes, exactly. And it usually should be quite stable at this time of year, so kind of trapping cold air above the Antarctic continent.

2:23but there's some emerging evidence to suggest that it's changes to sea ice cover in Antarctica that is weakening the wind speeds of the polar vortex. And when you have weaker wind speeds, you can have these warm air intrusions that can deliver sudden spikes in temperature to the continent. My colleague James Woodford, who's based in Australia, has done a great story on the current weird conditions that we're seeing in Antarctica and what they mean for Australia's upcoming spring and summer. You can read that now over on New Scientist. And you mentioned that this all seems to be linked to changes in sea ice in Antarctica.

2:58That's the story at the bottom of all of this, is it? Yes, exactly. That's one of the really big research themes that scientists looking at Antarctica have been covering and what the conference I was at this week was really focusing on. So usually Antarctic sea ice peaks in September, which is the end of the Southern Hemisphere winter, and it retreats to a minimum in February. Now, since we started using satellites to measure sea ice extent, that was back in 1979, the patter of ice cover in Antarctica has been pretty stable as compared to the Arctic, for example, where we've seen kind of rapid and steady loss of ice.

3:34But since 2016 in Antarctica, there's been a kind of sudden shift that scientists have been calling a regime shift, where we've seen a number of record low sea ice extents in the summer. and even in the last couple of winters, the maximum sea ice extent has hit record lows. 2023, in fact, was a record low minimum and maximum year, so a really kind of standout year for sea ice extent in Antarctica. And scientists are worried that this could suggest the continent has passed a tipping point of no return. We're going to find out why that might be in a minute. But it is true, isn't it, that the Antarctic has been neglected compared to the Arctic.

4:16Maybe the changes have been more subtle and now it's suddenly catching up. But why is it so worrying about these changes in Antarctica? Let's reel back to that. Yeah, sure. So unlike the Arctic, which is all ocean, Antarctica is a landmass that for most of the year is covered in both landline glaciers and surrounding sea ice. So the sea ice that surrounds the landmass helps to keep the ice that's on the land kind of locked away and safely frozen. And so it's not exposed to the warming and eroding forces that the ocean water would have. So if you get rid of the sea ice and expose the landline ice to the water, then that dramatically increases the threat of catastrophic global sea level rise.

5:01We're talking tens and tens of metres. Then you've also got the albedo effect of the sea ice. So white sea ice reflects radiation while darker ocean waters absorb it. So if you remove the sea ice from Antarctica, the oceans will warm more quickly and that will kind of accelerate future global warming. So it's a bit of a vicious cycle. And that's before we've even got to the impact on Antarctic ecosystems that rely on steady sea ice formation for their breeding cycles. So we've already seen, for example, mass mortalities in some penguin colonies because the sea ice is melting before the chicks can fledge.

5:39And so you mentioned that sea ice formation really seems to have changed since 2016. Have researchers made progress in understanding why, why that shift, why that time? Well, there's definitely now some consensus that this is well beyond what natural variability could look like and is therefore influenced by human-caused climate change. So at the conference I was at this week, Marilyn Raphael from the University of California presented some analysis, which basically her and her team extended the sea ice data from the satellite record that we have right back to the start of the 20th century with the help of using proxy data from Antarctic weather stations.

6:17And she concluded that based on this longer time series of historical data, the chances of seeing the record low sea ice extent that we did in 2023 is less than 0.1%. Wow, it does seem another catch up that we're only just being able to say that it's beyond the natural variability in Antarctica, where we've been able to say that for other systems years ago, that it's definitely a human caused climate change. So do we know what exactly is happening? Is it like warmer air or is it the warmer sea temperatures that's stopping the ice forming, like you were saying? Yes, so we're beginning to get some answers about actually the processes that might be at play that are contributing to the sudden shift in sea ice formation.

7:06The main suspects that researchers are looking at is warming ocean temperatures. So usually there's a current of warmer deep water in the Southern Ocean that's known as circumpolar deep water. And this normally is kept pretty separate from the cooler surface waters, which means that sea ice can generally form without any trouble across the continent. But we now suspect that a combination of changing wind speeds and changes to the salinity of the ocean, how salty or not the water is, is allowing this warmer deep water to up well towards the surface. So there's more mixing between the deep ocean waters and the surface waters.

7:48And because our oceans have taken up so much of the planet's excess heat over the last few decades, they've really borne the brunt of global warming. This deep ocean water is warmer than it should be. And that means that the sea ice can't form in the way that it should do to the same extent. And this does sound like one of those things that once it's changed, you can't change it back. Yes, changes to ocean circulation are generally pretty difficult to reverse. One of the big outstanding questions is whether or not we have triggered a kind of tipping point in the way the Southern Ocean works and the way sea ice formulates around Antarctica.

8:27One of the big uncertainties when we think about whether or not we could reverse this change in the future is how ocean circulation patterns might respond to the future melt of glaciers. So if you think about it, if you dump a whole load of fresh water from melting Antarctic glaciers into the ocean, you could essentially put a lid on this upwelling effect and the fresh cold water would suppress this upwelling impact and you would re-stratify the ocean. but we still don't really know if this would happen, the timescales at which this would happen and crucially it would still bring a huge amount of sea level rise for everybody else in the world even if it did work to stop future ice melt.

9:12Yeah, that uncertainty is such an awful thing and it just casts a huge amount of doubt and gloom over everything. I asked Edward Doddridge about this. He's an oceanographer at the University of Tasmania. He works on modelling Antarctic currents, and here he is on that. While each of these changes is concerning in its own right, my biggest concern is that we are starting to see changes cascading through different parts of the Antarctic environment. Sea ice lost in the summer enhances the breakup of ice shelves and causes ocean warming. These warmer ocean waters melt the remaining ice shelves faster, releasing fresh water that slows down the Antarctic overturning circulation.

9:53Each of these changes builds on and potentially reinforces the others. I wish I could say that we know what will happen next, but the truth is that we don't. Our scientific knowledge is always expanding, but Antarctica is changing so rapidly that we are struggling to keep up. Did you know that Yakult has an amazing amount of science behind its iconic bottle? Yakult's founder, the Japanese scientist Minoru Shirota, spent many years investigating intestinal bacteria. He selected and cultivated a unique strain of friendly bacteria, L. K. Sci-Shirota, and in 1935 the first bottle of Yakult was produced.

10:31Fast forward 90 years and Dr. Sci-Shirota's work is continued with passion by hundreds of scientists and researchers seeking future applications for this unique, friendly bacteria. For more information visit yakult.co.uk You've got a cat, haven't you, Rowan? I have Astrid. Great name, lovely name. So then you should know well how cats can pivot their ears to hone in on particular sounds. Yeah, like they can do it independently as well, can't they? And also it seems like they've got a life of their own. Yeah. Their ears kind of pivot to capture the sound like that. Yeah, quite jealous. Lots of other mammals have this too.

11:07And now it seems that a similar action takes place in our brain. So our brains sort of swivel to focus on sounds from different directions. Science writer Caroline Williams is here to tell us about it. She's the author of a number of books, the most recent of which is Innocence, How the New Science of Interoception Can Transform Your Health. Caroline, thank you so much for joining us. So apparently our ancestors 25 million years ago could swivel their ears. It's a long time ago, isn't it? But we haven't been able to do it since then. But our brain can do some version of this instead. Yeah, I mean, obviously we can move our heads to localised sounds if something happens that's particularly sort of attention grabbing.

11:45so we sort of have that ability but what we don't have is as Rowan was just saying the ability to just sort of swivel around and sort of you know scan the environment as if you've got sort of radar dishes on your head to localize different sounds that might be interesting but um this study has found that yeah we sort of have something similar on the inside but it only really kicks in when we start moving around and this is one of the reasons why we didn't know it until recently because until recently, if you wanted to get information on somebody's brain activity, you could put sensors all over their scalp and record their electrical activity through their brain.

12:21But they had to be sitting down and plugged into a computer. Whereas now we've got technology to do that using mobile EEG, which is sensors on your head, and it's kind of captured wirelessly as you move around. And so this is sort of opening up a whole new world of trying to understand how the brain works when it's doing what it does in real life, which is moving around, interacting with the world. Wow, so you could do so many different measurements if you are able to move around with an EEG on. So that really must open up what we can learn about the brain, Caroline. Yeah, and so what it's doing really is showing how the brain is able to sort of prioritise certain types of activity and functions depending on what's the most important thing at the time.

13:04So we're finding out that, you know, moving and thinking and perceiving is very much something that changes with action, because that's what our brain wants to do, wants to prioritise the best action in the world. So studies before have shown that movement sharpens our perceptions of the world around us. It enhances things like navigation, problem solving, you know, all these things that we might need to stay safe as we're moving around the environment. And so this new study builds on previous work that shows that our visual world changes when we start walking. So when we're standing still and then we start moving, we're more likely to notice things that happen in our peripheral vision, which is usually sort of filtered out as not very interesting or important.

13:47And then this new study shows that something similar happens for sound. So our brain sort of pricks up its ears almost when we start moving. But then as we turn and sort of move through the environment, it sort of turns up one side and turns down the other, depending on which way we're turning. So if we're turning right, we sort of listen harder on the right and less on the left. And then we sort of turn back. And it's constantly doing this thing like radar shifts under the radar. We don't really know it's happening. But the idea is that it's prioritising what's most likely to be important so that perhaps we can respond to the environment faster or better.

14:19So did the researchers behind this, is that what they suspected? And also, what does that actually mean in practice? Because we only have the same bit in your brain processing sound. How can it be switching from left and right? Yeah, so the researchers knew that this happened for vision, obviously, and they wanted to know if it happened for sound. But I don't think they expected it to be quite so dynamic as you're moving around. But what they did is they put 35 volunteers, they asked them to walk along a figure of eight path whilst wearing a mobile EEG cap, So it's sort of a cap with sensors all over it.

14:51And they also collected motion sensor data from their body so they could track, you know, put together the changes in the brain with the movements that they had. And they asked them to sort of walk around. And they were also playing continuous stream of sounds into both ears with in-ear headphones. So the sounds didn't actually change. What they were able to do is say, well, what's happening to the brain? Which side is it prioritising? And so the changes in brain activity when someone turned to the right was almost as if they would be the same response as if you turned up the volume on that side.

15:23So it's not so much that anything swiveling is happening. It's really a matter of attention. So the brain can only deal with so much information and the world's full of sensory information. And so the way it deals with that is by shunting attention to what's most important at the time. and so it's a shift of attention it's almost like you know if you're turning up and down you know if you're in a car stereo and you're turning the audio to the left and the right speaker well we know this happened you can we know that intuitively you can feel your attention shifting to different sides well like as a metaphor it does make me think of driving because as you're coming to an intersection you you turn to look a certain way because you need to look but i mean you're thinking your brain but i can actually feel my attention shifting if you're if you're focusing your attention to the left say and can our producer ollie can you mess with our heads here and like shift the volume from the left to the right and maybe we can demonstrate that am i shifting from the left to the right my focus is is switching yeah yeah it can be a bit disconcerting when it's happening in headphones and it's sort of shifting to one side and the other but but in this study interesting thing is it is the people who were doing the study weren't conscious of it happening so this is something that happens under the radar of consciousness and it's almost like that's I mean in a way that's why we didn't realize it that's why it's a surprising news stories because this is happening outside of our awareness but maybe it's there just to make sure that we can react to something if the kind of you know much fabled lion jumps out from your side you're more likely to be able to react faster because your brain has spotted it before you have so it's really interesting but what can we do with this knowledge can we use it in some way well one thing that it could be used in is to help um in the design of things like navigation aids so there are sort of smart canes available for visually impaired people that can kind of help give you a better idea of objects that are around in the environment also for maybe for hearing aids so the researcher who was behind this work um barbara handle said to me that you know one problem with hearing aids is that you have a lot of background noise but if you're out in a city environment and you wanted to turn and cross the road maybe being able to turn up that side would mean that you know and turn down the background on the other side would be useful to help you navigate the world but also you can imagine something like if you were doing um you know sat nav in your car it might be useful to have turn right be a little bit more obvious to you on the right hand side so um so yeah there's lots of interesting uh things so the other thing that it might help us to understand better is why there is evidence that exercise seems to be better for the brain for our you know for our cognition and our brain health if we're actually going somewhere and navigating in the real world compared to if you're just sort of on a treadmill or a bike looking at a wall.

18:12And this is all in your ballpark isn't it Caroline this is like what your books are about really move and the in a sense one as well tell us about interoception as well. Yeah so I mean that sort of fascinates me that, you know, what happens in the body, the brain cares a lot about. And so that, you know, movement affects the way we think and feel. And one of the reasons it does that is because it changes the interoceptive messages from inside the body. So interoception is the sense of internal body signals. So everything from sort of heart rate, breathing, hunger, thirst, I mean, some of these sensations are things that motivate us to move around and look for stuff in the first place.

18:48So I think one thing that's really interesting in this kind of research in people in the real world moving around and acting on it is that you can work out how the brain flips between sensory information from the outside from the inside of the body and then how it all builds this up into a perception of okay I'm here I'm now this is what I need to do and this is how I need to feel and this is how I need to act so there's a huge challenge for neuroscience to be able to put all this stuff together in moving people in the real world yeah it takes it to a whole whole new level so I think it's pretty exciting times was your dog listening with one ear by the side of you when you were talking.

19:24He's got one pressed up against the cushion and the other one looks pretty close to me. So he's tuned me out. Yeah.

19:33Now, on average, women live longer than men as far back as records go. And this is all over the world, all different cultures. The pattern holds the same. And in 2021, the average global life expectancy was 73.8 years for women and 68.4 years only for men. And what's less well known, though, is that there's a similar pattern across other mammals. So in other mammals, many other mammals, males live less long than females. And there's been loads of attempts to try and reconcile this. I've got a pet theory, which I want to get to later. I'm sure you do, Rowan. But here's a theory that's new to me.

20:09It's the idea that it's down to sex chromosomes, the X and Y chromosomes. and there's a really ingenious piece of work that's just come out to test that idea. Sam Wong's here to tell us about it. Sam? Yeah, so as you know, in mammals, if you have two X chromosomes, you're genetically female and if you have an X and a Y, then you're genetically male. But that's not the case in birds. So in birds, it's females that have two different chromosomes called Z and W, so they're heterogametic and in males, they've got two Z chromosomes, so they're homogametic. And in birds, it's typically the male that lives longer.

20:44Yeah. You know, it's a great way to test it, isn't it? So straight away, you think, OK, it's got to be something to do with this heterogametic chromosome. And there's also a lot about the disappearance of the Y chromosome in men, isn't there? And it's really disappearing in humans, but also in other mammals. Yeah, and we'll get to that. But I think when you say disappearing, you're talking about it shrinking. Yeah. But there's also other ways it's disappearing too. But Sam, tell us about the new study first. Yeah, so Johanna Stark at the Max Planck Institute for Evolutionary Anthropology and her colleagues, they looked at data on sex differences in life expectancy in loads of animals, 528 mammals and 648 birds, both in zoos and in wild populations.

21:27They found this dramatic contrast in lifespan. So in the mammals, in 72 % of species, females live longer than males, 12 or 13 % longer on average, And in birds, 68 % of the species, males live longer than females by an average of 5%. I'm intrigued by that. I appreciate the experimental design, but the sort of gender roles of birds is very different to what it is typically in mammals. So I'm interested in like how much of a comparison we can make there. But taking it as they did the study then, they found that mammals have longer-lived females, and that's the sex that has the two same sex chromosomes.

22:09But birds had longer-lived males. Similarly, that's the sex that has two of the same chromosome. Why then might that be the case? Yeah, so for most of your chromosomes, you have two copies, one from each parent. Yeah. And this doubling up is like a safety blanket. So if you have a mutation, harmful mutation in one of the chromosomes, you've got another copy of the same gene on the different chromosomes. So it's a way that you should be able to carry on working even if one of your genes is defective. But that's not always there with the chromosomes that determine sex. So female mammals have two copies of the X chromosome, but males have one X and one Y.

22:46So if they have any mutations on those sex chromosomes, they haven't got a backup. So in theory, females should be better protected against mutations than males. But the interesting thing from this study is that it does back up that idea that there's that chromosomal link. But there are many exceptions to the rule. So in mammals, there are some species where females live longer. In birds, there are some species where males live longer. So there must be some other explanation for that. I mean, and then it's not like the mammals are egg-laying mammals or something like that. It's more general than that.

23:15Yeah, it's harder to pin down what the difference is. But one clue that they found is that there seems to be a link with mating systems. So in animals where you've got polygamous mating systems and there's lots of competition for mates, so like our other relatives in the primates, baboons and gorillas and chimps, males generally die earlier than females. And this might be because males are investing in traits that help them to compete for mates. So larger body size, ornamental feathers or antlers. These traits are costly to produce. And there might be other costs linked to competition for mates like males fighting each other.

23:52You get injured and risk death. So in mammals, both the genetic factors and the sexual selection are working in the same direction to shorten male lifespan. In birds, you've got the genetic factors which favour male longevity. but there's variation in the mating systems. So if there's strong sexual selection, that might tip the balance the other way. And the human mating system is an interesting one as well. If you try to classify it like we do for other primates, it comes out kind of in between polygamy and monogamy and there's a lot going on. But can we look at the role of sexual selection in humans as regards to this?

24:29Yeah, as you say, it's a complicated question to answer what's the natural mating systems of humans. But compared with other great apes, we have less pronounced differences in body size between the sexes and males have smaller testes compared with their body size. So that suggests there's less competition for mates. And that fits with the longevity data because the difference between the sexes is less in humans than it is for chimps and gorillas. I want to draw a comparison between humans and birds because typically speaking, dads are very involved in bringing up human children. And that often usually is the case with birds.

25:03and I guess parental care must play a role here right you'd expect through evolution that if you do have a sex that invests more in raising offspring then it makes sense for that sex to live longer to really make sure that those offspring survive. Yeah that's something that they looked at in this study as well so in animals where there's a lot of parental care it tends to be the females that do more of the care and then there's an evolutionary advantage for the females to live longer so that they can keep supporting their offspring until they become sexually mature themselves. But there's also some strange exceptions that don't really fit any of the patterns.

25:36So birds of prey, for example, they're birds, so you would expect that the females would not live as long as males. But they found that females do live longer and also females are larger. They tend to engage more in the protection of the territory. So there's lots of reasons why you would expect them to not live as long, but they do live longer. Yeah, potentially that's like a riskier role. And yet for some reason they're living longer, despite having these two different chromosomes. Yes, that's right. And they don't have an explanation for that. Penny, what about the physical disappearance of the Y chromosome?

26:08Yeah, so there's two things going on here. I think often when we talk about disappearing Y, what people are thinking about is this common idea that the Y chromosome is shrinking and could vanish entirely. Yeah, which it is. Well, so it's lost more than 90 % of its genes. It's a small chromosome. But that doesn't mean it will disappear altogether. And apparently for about 25 million years or so, it's been relatively stable. So about the time that we lost our swivelling ears. It's a link. So I would say I'm confidently going to say no need to panic there. OK, that's good. Yeah. But I think more intriguingly, there's some evidence that we should be more worried about what happens at your own cellular level, because there is research that suggests that the Y chromosome can frequently go missing.