The evolution of sperm and the enduring mystery of the scrotum; How our brain rewires itself 4 times in life; The (real) disaster scenarios of imminent climate breakdown

0:00Are all batteries the same? That's like asking if all soccer players are the same. Take Messi, the most decorated player ever. Is there any other player who has achieved that? No, just him. Now take Duracell. Is there any other battery with power boost ingredients inside? No, just Duracell. Remember, goats only trust goats because they're built different. And Messi only trusts Duracell. On the show this week, the evolution of sperm and the finding that sperm actually originated before animal life as we know it. I could say that we are all sperm that have evolved an extra life stage where we have a multicellular body.

0:42You could say that. Probably no one else will ever say that. We're also revealing that the brain ages in five distinct stages. Nice. This was a really intriguing study, especially because it suggests that adolescence may actually extend into our early 30s, Which could explain why some days I do feel like a teenager. We're also reporting from the National Emergency Briefing in London I've just come from. That's set up to alert people to the escalating threats to society and to the world in general from the climate crisis. They really emphasise the connections between things, connected to our health, to our security, biodiversity, the economy.

1:19All these things are connected.

1:24Welcome to the world, the universe and us from New Scientist. I'm Dr Penny Sarshan. And I'm Dr Rowan Hooper. So shall we talk about sperm then? Yeah. So about the origin of sperm, the evolutionary origin. Now, as you know, there's this concept in genetics and origin of life studies called the last universal common ancestor. Yeah, also known as LUCA. That's the single-celled organism that all of life today theoretically traces back to and doesn't exist anymore. We'll never find it, but we can try to reconstruct it. We can look at genes, work out what it must have looked like. are you going to say that we can do that for sperm?

1:57Well that's it, that's today's story. The last universal common sperm is the story Great. And so if you we can give it an acronym, the last universal common ancestor of sperm or Lucas. Lucas! Yeah is the name. Sam Wong's here to talk about it. Sam, how do we recreate Lucas? Well we can look at the proteins that make up sperm in living animals and we can look at the genes that code for those proteins and work out how they're all related and from that we can deduce what the ancestor of all those sperm looked like and also work out when their ancestor lived. And that's what Arthur Matt at the University of Cambridge and his colleagues have done in a study that we reported on this week.

2:32So this sperm toolkit then, tell us about what it is and what it suggests about sperm's origins and this intriguing suggestion that it predates animals. So there's a toolkit of around 300 gene families in living animals. So they're widespread in animals today, but they're not only found in animals, they're also present in some single-celled eukaryotic organisms that are related to animals, like coanoflagellates, which are, they look quite like a sperm actually, so maybe it's not that surprising, but they have a swimming tail called the flagellum, and the protein toolkit that they use is very similar to the toolkit in sperm.

3:09So that suggests that we've inherited the molecular machinery of sperm from a single-celled ancestor that predates all animals. You could say that we are all sperm that have evolved an extra life stage where we have a multicellular body. You could say that, but probably no one else will ever say that. You are a sperm. Uncomfortable fact. It's one of these stories that when you first told me about it, it just made complete sense that there would be, of course, there would be pre-existing parts that are clobbered together like a kind of frankensperm to make something. Of course, it's not going to just leap out of nothing.

3:43But sperm are incredibly diverse in shape, aren't they? And I did work on them a bit in my PhD on sperm variety and diversity. But this study, Sam, it showed that the innovations that led to all this diversity in modern sperm that we see, they've mostly been on the head of the sperm. And the tail hasn't really changed much since that common ancestor. Yeah, that's right. So sperm have evolved a lot, as you say, they have to work in lots of different environments. So for example um our sperm have to uh the sperm have to find an egg inside a body whereas lots of lots of animals the sperm is sort of free swimming in the ocean or in other bodies of water so they're working in different environments they need to have different specializations for that but yeah most of that change has happened in the head whereas all of all sperm have to swim so they all have this kind of swimming tail and that bit is really conserved it hasn't changed very much throughout the course of evolutionary history i am actually quite surprised that we didn't know this already because this is something that I wondered about years ago first learning about like you say single-celled eukaryotes like complex cells often have these flagelli and they're so like sperm structurally they're very very similar but now we're only really now kind of making that link in in the research yeah that's right um I think people yeah I don't don't know why but somehow they hadn't really put it all together yeah it does make sense I think they've been a sort of anatomical yeah but this is a genetic yeah to kind of underpin that and i hate to be that person who always talks about plants but that um that idea you suggested that we're all sperm really and we've just kind of got this add-on stage where we're multicellular early plants were like that too originally it was the sex cells that were the dominant part of the life cycle and then they they just spun off this tiny little phase where they they happen to not be sex cells so it's quite interesting to think that that's at the core of being a eukaryote yeah anyway you You know, any good sperm anecdotes from your PhD?

5:33How long have we got, actually? But talking about the tail, there are some species where the sperm join together, so they have twin access to double power to swim up. I've seen in some mammals, opossums have the sperm twin together. They're little buddies. Yeah, but then they turn to enemies at the end, right? Wow. Because only one can fertilise the egg. Interesting. Yeah. And then some of my favourite sperm, just as I was saying, it sounds a bit strange. Not a great phrase, yeah. But if you work on this stuff. So the great water beetle, Ditiscus, that's got giant sperm. I remember dissecting it once and looking at the sperm story.

6:11How big are we talking? Well, so the beetles are, you know, about a centimetre long. Yeah. And the sperm, it comes out like spaghetti out of the thing. Really long. Like probably over a centimetre long. So it comes out. It's huge in this insect. So it's got giant sperm. And then Lepidoptera, of course, most of them, most of the ejaculate has no DNA in it. By which we mean, we're talking butterfly and moth now. Yeah. Most of them, half the sperm have no DNA. So what's the point of it then? Well, it's a whole huge mystery. Really? Yeah, yeah. It's a really interesting evolutionary mystery. What is that anucleate sperm for?

6:49So we can't get into that now. But what we can get into is something that really has bothered me for ages. is this basically ridiculous situation that male mammals have got themselves in, that the testes are housed outside the body. So, you know, these are, in an evolutionary sense, the most important thing that we have, right? And we don't have, you know, our brain is in a nice protective skull. The testes are just hanging in a sack, like so vulnerable, it's ridiculous. It is ridiculous, but I guess it works. and one of the ideas is that to make sperm you need cooler temperatures and that's more doable if they're outside yeah but that's always the story but it just never made sense to me but sam has i know you've got a good understanding of all this so take us through it well so as you say it leaves leaves us quite vulnerable to to injury and and it's not the case for for all animals so you know fish amphibians reptiles birds they all don't have scrotums and even in mammals it's only mammals that have scrotums, but lots of mammals don't have them.

7:51So there must be some reason why it's so widespread in mammals. Why does the sperm have to develop at a cooler temperature? So if you look at the evolution, it looks like scrotums evolved twice in mammals. In marsupials, the males have scrotums, but they hang in front of the penis. So it looks really bizarre if you ever see kangaroo's genitals. And in our branch of the mammal tree, there are some animals that had a scrotal ancestor and then they evolved back to not having a scrotum. So whales and dolphins, obviously, if you're in the water, it makes sense to not have a scrotum. But also elephants, rhinos, hippos, hedgehogs.

8:25So all of these animals have gone back to not having a scrotum, and we're not really sure why. So why are there these differences? So if, yes, scrotality has evolved twice, to use the technical word, and it's persisted in most mammals, there must be a good reason for it. The first proposed explanation is that sperm development needs to happen at a lower temperature. And there's lots of evidence for this. There were some experiments in the 1890s where some poor dogs had their balls pushed into their abdomens and sewn up and the sperm basically stopped developing. And then in men now, you see that there's a link between wearing tight pants and lower sperm counts, less viable sperm.

9:00And there is a lower temperature in the testes as well. Yes, that's right. It's considerably colder. But that raises the question why sperm development evolved to need a lower temperature. So warm-bloodedness evolved about 100 million years before the scrotum. So having warm balls wasn't always a problem. So there are a few possible explanations. We still don't know which one is really correct. But one idea is the display hypothesis, which is saying that external genitals are important for attracting a mate. And that fits with this idea in evolutionary biology called the… Honest signaling. Honest signaling, that's right.

9:34So Amat Sahavi proposed that males have these costly ornaments like the peacock's tail or whatever. that are on a signal because they're so inconvenient, it shows that you must be a fit and healthy male if you can carry around these ornaments. But that doesn't make a whole lot of sense because scrotums are not that conspicuous in most animals. Unless you're a vervet monkey and you've got a bright blue scrotum. And I think it's the higher ranking males have the brightest balls. And when they go down in rank, unfortunately the colour turns down. So that is an honest signal of status. You just look at the ball colour of these monkeys.

10:18But as you say, it's not a universal explanation. For those of us who don't have bright blue balls, there must be some other explanation. Moving swiftly on. So there was an idea put forward by a guy called Michael Chance in the 90s. I found a New Scientist article about this. He read in the newspaper after the Oxford and Cambridge boat race that the rower's urine contained prostate fluid, apparently because the exertions of rowing raised the pressure inside the abdomen and squeezed out some of this prostate fluid. There's no sphincters in the reproductive tract to keep stuff in. So he said, well, if the testes were inside the body, then when you were doing running or rowing or whatever, then it would be squeezing out the sperm and that would be a waste of sperm.

10:59So he looked across all of the animals and he found that the ones that have a scrotum are the ones that have to do a lot of leaping or galloping. And it's these kind of really high energy movements that would raise the pressure in the abdomen and would be forcing out the fluid. And therefore they need to have the balls on the outside because it avoids this pressure problem. So that's an interesting idea, kind of appealing. But then you think, well, why don't we just have a sphincter that keeps the reproductive tract closed and stops them from getting pushed out? You know, not all of us exert ourselves like we're in the boat race all the time.

11:36And so in order for just that possibility, we have to have a scrotum all the rest of the time and all the dangers that involves. What was the starting hypothesis? I'm just going to collect the urine off a bunch of rowers after this race. I don't know. I think that was an unrelated study that he just happened to see that there was a result. But, you know, about the evolution of a reproductive sphincter, I was thinking about this, about the penis bone, because we used to, when I say we, like humans used to have a penis bone. Chimpanzees still do. Chimps still do. It's quite widespread in mammals.

12:09Yeah, but we lost ours. So maybe there's something in that, I think, in that the penis bone, the lack of a penis bone in humans is probably another honest signal. Because it means you can't fake an erection. Hmm. But that is the explanation. Absolute marmalade. Sorry, Sam. Go on. I've lost my train of thought. You're speechless. I'm just wondering, so are you suggesting that chimpanzees do fake an erection? Yeah, they do fake it. They just run around with an erection. But is that fake? Surely that's a real erection. No, it's not a sign of quality. Right. whereas should we do a special episode on penis bone yes please later on yeah maybe a bonus further down the line time for a word from our sponsors Deep what's it like to really live on the ocean floor head over to the New Scientist CoLab podcasts to journey to Vanguard a next generation subsea habitat where you can crawl through hatches like a space station have giant fish as nosy neighbours and become a real aquanaut.

13:21Discover the future of ocean exploration at New Scientist CoLab Podcasts, available wherever you get your podcasts. Many of us feel like we go through phases in our life. Right now I'm in my podcasting era. But seriously. But Taylor Swift. Yeah, exactly. We'll get to that in a sec. But in seriousness, research is beginning to show that often when we feel like we've passed through into some other kind of stage of life or we've aged somewhat rapidly. It's starting to look like this could also be true on a biological level. And there are these multiple dramatic physiological changes that occur throughout our lifetimes.

13:58This week, a new study has suggested that there are four major turning points in how our brains are wired throughout our lives. And health reporter Carissa Wong is here to tell us more. Yeah, this was a really intriguing study, especially because it suggests that adolescence may actually extend into our early 30s. Which could explain why some days I do feel like a teenager. But first, it's helpful to understand kind of how the brain is organised. So the brain has many distinct regions, which are each involved in a specific task, like memory or learning a language, those sort of things. And these various brain regions talk to each other through these wiry structures called white matter tracts, which essentially pass information from one region to another, allowing the brain to sort of act as a whole.

14:44And it's this wiring that's really crucial for like putting together our personalities and our cognitive abilities. Wow. And so this wiring itself changes with age, these connections. I mean, the tracts between the areas changes with age. Yes. So researchers analyze MRI brain scans from about 3 ,800 people from the UK and US. And they were aged between birth and 90 years old. And none of them, or mostly none of them, had neurogenic conditions or any mental health conditions. And what they found is that the brain's wiring seems to go through four key turning points. And these are at age 9, 32, 66 and 83.

15:25That's specific, isn't it? Yeah, let's probe that in a minute. So the first phase occurs between birth and nine years old. And during this phase, the brain's sort of connections between brain regions seems to become a bit longer and convoluted. So in a way, a bit less efficient. So I think we already knew that brain growth is incredibly rapid in children, especially like these first three years. But what does it mean if those connections are more convoluted? Does it mean it's like information being sent across the brain? It's taking longer, it's taking a more circuitous path? exactly so that's what we mean by it gets less efficient in that era wow and so why do we think that happens so as you just mentioned in our very early years we do have like this proliferation of connections between neurons in infant brains and then as they age through to about age six seven or so some of those connections are pruned off as we experience things and grow like our useful ones are reinforced and the ones that aren't so useful are sort of removed.

16:29I'm really interested in this, just to interject, because it's sometimes talked about as like a pre-adolescence or a secret puberty. And it's not often talked about, but there's a real change that happens in children at that age. And Alison Gopnik, a really famous developmental psychologist, I read a phrase of her, and I'm sure I'll misquote it, but once she sort of described like there's no one on earth more serious than a six or seven-year-old. And it's because they're going through this kind of change at that time. Yes, exactly. And so this process creates a really nice broad range of useful connections, helping you learn things like languages or how to play the piano.

17:03But it seems that the side effect of this is that, yeah, you get a less efficient wiring in the brain. Wow. So I have a child about to turn nine. What happens at this age? Yes. So around age nine, this is the beginning of the next phase. And researchers think that this might be triggered by puberty. So like hormonal changes happening that can affect how the brain develops. But it could also just be that thing of, you know, the pruning process that is so crucial in those early years, sort of winding down and pushing you towards this new phase. And the next phase is essentially from age nine to 32.

17:40And that's sort of where you have an increase in the efficiency of the connections between brain regions. I mean, this is bonkers, isn't it? Nine to 32. If you compare your daughter with not making assumptions about your age, but you said you still feel like a teenager, so early 30s. Like so many changes are happening within us to us during this time period. The idea that that's a sort of fixed term of cognitive development is quite out there. Yeah. So they're not saying that between age nine and 15 and 25, we all have the same brain. Yeah. It's specifically when you're looking at this very general sort of picture of the brain's wiring, that you see this same pattern of increasing efficiency.

18:20And so that's why the researchers sort of lumped them together in a phase. Okay, so it's a population level look, and that's why you get these sorts of patterns. So you go from getting as many useful connections as you can in phase one and then to pruning, making those connections more efficient. But the second phase, does that imply that adolescence, is this what you're saying, that adolescence, this phase, this transition, lasts really that long? I mean, if the brain's still really increasing its efficiency, even into your 30s. That is one way you could think about it. As I mentioned, like, yeah, it's a phase from 9 to 32.

18:57And adolescence is that transition from childhood to adulthood. So, yes, maybe you could conclude that. But it's important to remember that the way we define adolescence is going to differ depending on what measures you're looking at. Yeah, so I want to bang the drum for grey matter here because this is about white matter. and I saw a lot of places this week have kind of run with the idea that oh we're adolescents into our 30s and I think that chimes that I get possibly because I'm in my 30s I get a lot of jokes on social media about like I have a career in a house but I just feel like a teenager so I think we all want to believe it right but if we think about grey matter which is the bodies of neurons they connect together also really important we know that in adolescence there's this extensive pruning of grey matter.

19:43Like after all of this proliferation in your childhood, it's the time to really boost efficiency, which sounds like it's the same with white matter. But the grey matter remodelling is amazing. It goes from the back of the brain and then works its way forward. And we've known for a little while now that the last bit to get remodeled is the prefrontal cortex, where we make good decisions. But that gets done by about the early 20s. So, okay, maybe by white matter measures we're still teenagers into our 30s but we should be able to make better decisions and behave like grown-ups in our 20s you can't lean on this result to say that's why i was an asshole yeah that's what i'm saying okay i still think it's really interesting though to kind of get this view and often we don't talk about white matter and so what's the next one then carissa 32 what happens at that point so from 32 to 66 we see this efficiency trend sort of flip back to decreasing over time.

20:36Is there a crumb of comfort for someone who may not be in their 30s anymore? Yeah, so while there is some decreasing efficiency, it's actually very gradual. So the changes that happen in this really long phase, the longest of all the phases, are very subtle actually. So you could sort of think it as like a stable phase, which is a bit nicer, right? Then you hit the next phase, which runs from 66 to 83. And during this period, it kind of seems like the brain seems to maintain the connections between neurons within regions but the connections between different regions seems to sort of weaken relatively to that and that's quite interesting because like around this age you get more risk of things like Alzheimer's, dementia and so while we don't really know from this study exactly how this links the brain wiring to those conditions it is certainly interesting to see a difference here.

21:30Yeah it's intriguing to see that correlation isn't it because the risk for dementia really does go up around this time with this transition. And then what's the phase that comes in after 83 then? So from 83 to 90, because 90 was the oldest participants that they had in this study, they see a general weakening of connections between brain regions. But also this interesting thing happens where the connections are going through these hub regions more. So it's like as you wear and tear and you age, your brain is being very careful with where it puts its resources and it seems to find it more efficient basically to make connections run through certain fewer regions rather than maintaining them broadly everywhere you don't want to over interpret it but like i do feel like you can almost imagine what that's like when you're younger everything's sparking and it all connects up and then as you're older if you're really tired um you kind of have to force the information through these key hubs and that sort of slower but you don't you don't know if that's what we're really experiencing do you know and what about after 90 though is there any ideas about that i know that the this study stopped at 90 but what about what happens after that yeah i did ask the researcher about this and she said you know anything could happen really after that it could be a new phase it could be a golden era who knows but they didn't have data to explain that um it could also be that the phase the last phase we described just continues and so you know we've got some really specific numbers here 66 83 um but this is all from averages like how generalizable are these really do we do we all fit into these neat categories they almost feel like horoscopes right we just kind of oh that's who i am but are we all going through these defined same number of phases that's a really important point so this study is like averaging people across a population and so for a certain individual i asked the researcher could you have one era two eras like 15 eras and she was like well it's it's possible we don't know how how far that ranges between people and it's also important to note that not everyone is going to hit these phases at the same time so some people might hit a phase earlier later we need to look more into that i guess we write a lot in new scientists about things you can do to slow your brain aging or boost your cognitive reserve so that that suggests that you know this isn't destiny you can get beyond yeah is there any idea about that because if you can find people who um who can delay the decrease in efficiency of their brains maybe we can learn something about that and then apply it to the rest of us exactly so this is why it's so interesting to see how these phases change over time how it links to cognitive function and health and how it differs between people the idea is that we understand what's driving those changes whether it's environmental exposures or genetics or something else we could start to pinpoint exactly maybe ways that we can sort of alter these things and if you compare sort of you know the average healthy brain aging to conditions like mental health or neurodegenerative disease you might be able to find out as well like how your brain wiring might be changing sort of your risk of those conditions.

24:41I saw in your article Carissa that you note that some of these sort of tipping points or turning points do correlate with key things that we know happen with the brain so like we've already said dementia around 65 66 but also many mental health conditions are usually clear in by the time you're 25 say exactly so this kind of information can help us understand why is it that certain phases of life seem to put us at greater risk of certain conditions as you say like mental illness but one thing to be wary of is that these studies were based on people in the UK and US and the participants but also mainly white.

25:15And it is important that we look at a more ethnically and geographically diverse range of people when we sort of want to make these general assumptions about how our brains are wiring. Now, on Thursday morning, I attended the National Emergency Briefing in London. And this is an initiative set up by climate activists and funders and scientists. And they've invited like 10 world-leading experts across a range of subjects, climate, weather, food security, health and so on. And economists as well were there. And each one gave a short presentation on the state of the world. And the message across the board is that the environmental breakdown is biting harder.

25:56It's escalating faster than expected. And it was very powerfully put because these people were not your normal sort of activists that you might see, you know, with a woolly hat on, waving a flag. You know, these are world experts. There was this guy, Hugh Montgomery, He's a professor of intensive care medicine at UCL. He's a professor of emergencies, and he showed images of his emergency room. He said, I deal in emergencies. That's what I do. We are in an emergency, and we have to treat it as such. And he referred to this Lancet report showing that the biggest health risk of the 21st century is climate change.

26:34And about the future, he said, it's not about, it's no longer about risk. It's about survival. So it becomes very stark the way they were talking about. Michael LePage was with me at the meeting. Michael, what are your takeaways? I think the meeting had a really powerful effect on me. There's no single thing that people said that was new that I didn't know about or that we haven't reported on. But having a series of talks lay it out in such sort of clear, stark terms, one after the other, was really powerful. So, for instance, we had Kevin Anderson at the University of Manchester warning that there's a small but real chance of a four degree Celsius rise in temperature, which would have all sorts of devastating consequences and probably lead to societal collapse.

27:17we had tim lenton at exeter talking about tipping points and how if the atlantic overturning circulation collapses that would lead to consequences that include these really severe winters in the uk where the temperatures in london will go down to minus 20 yeah the north sea would freeze over yeah he showed the ice sheet how it would goes down all as far as south as the wash in the uk the arctic ice sheet just that far just incredible and that would basically he said that would basically lead to the end of food production there'll be no more farming in uk it wouldn't be possible so that's a really serious risk i mean we had other people talking about how you know we already seen the impact on food we you know if you had in the uk they've had sort of three of the worst harvests ever in the past decade that's already hitting uh sort of food prices and contributing to the cost of living crisis so there are all these reasons to be Yeah, I think, as you say, it wasn't anything that we, new scientists, involved in this stuff and reporting over the years were not aware of.

28:20But it was still very powerful to hear it packaged like this. And I think if it is, if it does this message and they are going to try and get it out as widely as possible, then hopefully it will get, it will shock more people. I mean, maybe the idea is to shock people, to scare them. Yeah, I think we seem to need that because not enough is happening. As I wrote about recently, we've seen four years where the predictions for how much warming there will be have not changed at all because there's been no effective action, no new sort of policies announced. And so we're heading for a very sort of serious future.

28:58You mentioned Kevin Anderson at the University of Manchester. He spoke about what we need to do and to not be diverted by solutions that don't work. and in fact focus on the ones that we know do work. And here he is talking about that. If we're serious about trying to live on our Paris commitments, and I would say this is now the weaker end of that, the two degrees C framing, there are two absolute prerequisites. The first one is we need to deploy technologies as rapidly as we possibly can. But these are technologies that are not pseudo-technologies, not technologies for tomorrow. They're the ones we know how to do today.

29:34You know, retrofitting our houses, public transport, all of these things that are the non-sex end of the technology, we know how to do and we can do it very quickly. I think a lot of the more exotic technologies are more of a delay tactic than they are a meaningful technology to deliver on climate change. Climate change, the most important element to understand is the time frame of response. That time frame takes me to the second prerequisite, is we've got to reduce the energy consumption amongst the relatively high emitters in our society who drive most of the emissions. And that's a large but still levelless minority group of relatively wealthy ones amongst us.

30:08Now, one of the other speakers was Lieutenant General Richard Nuge, a retired former general from the British Army, with loads of experience around the world in different combat zones, basically. He spoke about the threat of climate change to national security. And he said, and this is a general, you know, it's not, like I said, it's not like a tree hugger type person. He said we're facing the possibility of an ungovernable state. And he mentioned Churchill in his presentation. Afterwards, I asked him a bit more about that. He said Churchill called out the threat that we faced during the start of the Second World War from Nazi Germany.