Anthropologist Chris Stringer of the Natural History Museum in London talks about Neandertals. And Scientific American's Kate Wong, co-author with Donald Johanson of Lucy's Legacy, talks about the discovery and impact of the famous Lucy fossil. Plus, we test your knowledge of some recent science in the news. Web sites related to this episode include www.snipurl.com/lucyfinder; http://bit.ly/bntu0

Podcast Transcription

Steve: Welcome to Science Talk, the weekly podcast of Scientific American posted on October 23rd, 2009. I'm Steve Mirsky. In this episode, we'll talk human evolution with renowned anthropologist and Neandertal expert Chris Stringer and with Scientific American editor Kate Wong, coauthor of the new book Lucy's Legacy: The Quest for Human Origins. First up, Chris Stringer. He is a fellow of the Royal Society and holds the title of research leader in human origins at the Natural History Museum in London. His most recent book is Homo Britannicus: The Incredible Story of Human Life in Britain and that's the first subject of our conversation.

Stringer: Obviously there was an old view that when people got into Britain half a million years ago, they were always here right through to the present. And we now know that's completely wrong; [that] actually what happened about every hundred thousand years, when there was the peak of an ice age, Britain got cleaned out of people entirely and then had to be recolonized all over again. [And] remarkably, 125,000 years ago, when Britain seemed to be an island perhaps strongly for the first time, nobody got back. So you had a warm period with hippos and elephants and tons of [stuff for people to eat] and no one was there, and the Neandertals did not have boats and they couldn't get across the English channel.

Steve: Wow!

Stringer: So for 100,000 years, Britain had no people on it even when the climate would have allowed it. Eventually, the Neandertals made it back, when sea level fell again. So you've got these episodes of human appearance and then people just disappear. People were only in Britain might be for 20 percent of the time in the last 700,000 years, which is incredible, you know, [for] the old idea of continuity of occupation.

Steve: And by people you are including all Homo species.

Stringer: Yeah, so we think now obviously there's the species identified from Southern Europe Homo antecessor, pioneer man, that the Spanish have identified at Atapuerca, and probably that could have been the first species into Britain moving up from Southern Europe in [warm] stages. Then we think we have Homo heidelbergensis, such as a[t] Boxgrove. Then later on the Neandertals, so from about 400,000 on which whenever people were in Britain for 300,000 years, it's Neandertals, evolving Neandertals. And the Neandertals were in Britain until about 35,000 years ago and then at 30,000 years ago we become modern people as a ceremonial burial at Paviland of Cro-Magnons and it was in fact probably the first one ever found, and it was dug up in about 1822, and because they had no concept then of what it was, it was thought to be perhaps a prostitute servicing the Roman army because this individual had red ochre powder on them and ivory jewelry. So they thought it was a woman. In fact it was a man, so it was nicknamed, it was called the "Red Lady of Paviland". In fact, you know, it's a man. We have learnt quite a lot since 1822. And that's a [burial that's over] 30,000 years old. Then those modern people were in Britain, even they couldn't survive the peak of the last ice age. So about 20,000 years ago, the last ice age reaches its peak, even those people, the moderns, can't survive and Britain has to be recolonized [all] over again after the peak of the last ice age, so it is an amazing story.

Steve: You mentioned evolving Neandertals; so what you are implying there is, the Neandertals of 300,000 years ago were different from the Neandertals that were the last ones to be there 35,000 years ago.

Stringer: Yes certainly. We contract the evolution of the Neandertals and [obviously] people use the term differently, so different people use different ways of defining what is a Neandertal. For me, the Neandertal lineage, we can see it's beginnings at Swanscombe in Kent at 400,000 years, and at Atapuerca, where there is this pit of bones full of the remains of fossils. That's the transition between Homo heidelbergensis and Neandertals. They show [a mixture of] features of the two species. So I think the Neandertals are beginning certainly by about 400,000 years ago, then they gradually evolve to the final Neandertals, the ones we know best from Europe in the last ice age. And so the brain size increases, they develop more specialized body shape, the technology, [of course,] changes as well. So the Neandertals are evolving through time in parallel with [our own] lineage because there was this split, it might be around 400,000 years ago. So Homo heidelbergensis goes in two different directions, north of the Mediterranean, it becomes Neandertals, south of the Mediterranean in Africa [it] becomes us. So I see these two species drifting apart more than some sudden schism. What happens is that the Middle East and the Sahara gradually become more powerful barriers to human movement and so the former wide-ranging species, heidelbergensis, gradually gets divided, so in between the Middle East with increasing severe cold, as populations get separated increasingly and then go their own way.

Steve: [I always] think of Neandertal as the view back, the reflection in sort of a fun house mirror. It's almost us, but it is very different from us at the same time. And as a person who researches the Neandertals, what is your, kind of, instinctive reaction when you study these people? These are human beings.

Stringer: Well, yes, I mean they have obviously gone through, themselves, a lot of image transformations. So in the late 1800s and early 1900s there were no really primitive humanlike fossils that we had; nothing from Africa of the very early stages of human evolution. So Neandertals were pushed into that position. So around 1900 they are being reconstructed as ape men—stooping, hairy, grasping big toes and, you know, we know they are not like that. They are very evolved humans, their brains was big as ours and in some cases even bigger than the modern average. So they are actually highly evolved humans, but equally they are not the same as us and so Carlton Koons' classic thing was, if you took a Neandertal and washed and dressed him with modern clothes, put him on the NYC subway and no one will bat an eyelid, and as I said yesterday, [that] probably says more about the NYC subway maybe than it says about Neandertals.

Steve: Nice.

Stringer: Because I think they would have been different. I mean Steven Jones has made the point that, you know, again with the subway analogy, that if a Neandertal came in, if a Cro-Magnon came along and sat next to you on the London underground, you might move seats, because he [would look] a bit odd. But if a Neandertal came [and got on], you might change carriages. That was so, I think they would have looked quite different. Because in terms of time, allow in a separation. If you think of the people that met each other in the colonization events of 200 or 300 years ago, so Europeans got to Australia and met the Aborigines, they got to the Americas and met the Native Americans. Those populations had may be an effective separation time of, let us say 40,000 or 50,000 years with the spread of modern humans out of Africa. When Cro-Magnons met Neandertals they were meeting groups that they have been effectively separated from may be for 300,000 years. So you can multiply, however different we look to each other today and behave differently and cultural behavior everything, you could multiply that two or three times probably to project how different the Neandertals would have been. And we can't imagine exactly but I think they would have, I think, would we have seen [them as] human? Yes. I mean they walked upright, they obviously had technology and things like that, but I think they would have been more different than anything we can imagine today looking at the variation in modern people.

Steve: You mentioned culture, now culture does not fossilize, behaviors do not fossilize. We might have some archeological record, but it seems like the behavior armamentarium of the Neandertal was very different; the cultural aspects of Neandertal life were very different from Homo sapiens. And so how much of that do you think played a part in the fact that they are not here anymore versus just they are in physiology?

Stringer: Yeah, I think obviously behavioral differences were also a big part of their story and, of course, we came out of the same sort of cultural background as the Neandertal. So our ancestors obviously shared large bodies of behavior and technology. And then even 100,000 years ago, if you could look just at the stone tools that modern humans are making in Africa and Israel, they are really hardly any different from what the Neandertals were doing. But then things obviously increasingly changed, and so by the time you get to 40,000 years ago, [in my view] there is really quite a big gap that [has] developed between the modern humans and the Neandertals in terms of technology. So when moderns come into Europe, there was a much bigger gap there then there was a 100,000 years ago between the two groups. And I think that the reason why the Neandertals went extinct is it's certainly not the simple thing that we thought even 10 years ago; you know, I think, I would have said, well, yeah, moderns came in and Neandertals just very quickly just conceded, they were inferior, modern humans was superior technologically and the Neandertals just went under very quickly. And we now know it is a more complicated story, and so I think that, we focus because the best evidence is in Europe, say 35,000 years ago that is obviously where if one focuses their attention, and it possibly was the very end of the Neandertal story. I mean [maybe] they survived in pockets somewhere else, but that is where we know they survived last, so everyone focuses in on that time. But of course, modern humans and Neandertals range much more widely than that, so when modern humans came out of Africa might be 50,000 years ago, 55,000 to 60,000 years ago, they would actually probably encountered Neandertals in Western Asia and as they moved eastwards and on to southern Asia, they may have encountered Neandertals in Uzbekistan and Siberia, so actually it probably was quite a wide-ranging process. So as I said before the reason why Neandertals went extinct probably was not down to one single cause; there would have been different causes at work and combination of causes in different places. But in Western Europe, I think it was a combination of the arrival of people with superior technology and climate change so the Neandertals were doubly unlucky, because at the time modern humans came into Europe, the climate of Europe was extremely unstable. It was fluctuating very rapidly, every few thousand years it would switch very quickly from relative warmth to deep cold. Now they had coped with that before, by just retreating back into refugia, so they would just die out in wide areas including Britain and Northern Europe and they would retreat to the (unclear 10:34) or the Mediterranean, and then when things improve[d] they['d] bounce back. But 45,000 years ago there was another population [that] arrived and then they had to cope not only with these fluctuations but the competing population. So [at a] time when the carrying capacity of the environment was crashing and it could support less people, less hunter-gatherers, suddenly there was another lot of people there. So I think, it exacerbated the problems and by 30,000 years ago—I mean, modern humans would have been impacted by these severe changes too, and their populations crashed as well, but somehow we got through it and the Neandertals did not. So I think it was that combination in Western Europe that did [it] for them, and if they [had] had a stable climate situation [may]be they would have partitioned the environment, the two species, and somehow both could have survived even until today, but that combination did [it] for the Neandertals. I think, we, even a small percent of superiority in your ability to [deal] with cold, so we [know] modern humans had needles; they probably had sewn clothing, whereas Neandertals probably fastened their clothing together. If you can sew your clothing, you could make much better insulating clothing, much better tent structures to shelter. Modern humans had much more complex technology, I mean, you can compare Neandertal technology, it was very good at what did. Imagine a knife and fork they are really good at their jobs, but with modern humans you['ve] got like the equivalent of a whole tool box with spanners and pulleys and weaving and high temperature firing for even making clay statue[ttes]; all of that technology I think, just takes moderns that bit further than Neandertals.

Steve: All the geneticists, I know of who study this think that there is no genetic evidence for interbreeding between Neandertals and modern Homo sapiens, and from your point of view [does] that sound like a reasonable stance?

Stringer: Well, it is certainly, it a stance that I have argued for a long time, but on the other hand, to be fair to the geneticists there are some who, I mean, Henry Harpending has just published a book called, I don't know, The Last 10,000 years of Human Evolution [or something like that], where he argues that in fact Neandertals did contribute, and he is a distinguished geneticist. So there are still some geneticists who argue somewhere there will be some surviv[ing] Neandertal genes but yes, I am with Svante Pääbo if you like on the conclusion at the moment, the evidence for interbreeding is very thin, it is minimal. But that is not to say it did not happen. So if we look [at] us and Neandertals, as we have said, I think they would have been quite different to modern humans in many ways. But on the other hand, human behavior—say the vagaries of human behavior—imagine that these things could happen sometimes and genetically these populations are very close. I mean even a separation time of 400,000 or 500,000 years, Neandertals were closer to us than even some groups of chimpanzees are genetically, you know, chimpanzees' species have been diverging from more than a million years and zebras and horses for example, have been separated for more than [a] million years, yet they can still hybridize. So for Neandertals [and] modern humans could be probably possible, but I think that for the populations, it probably was not something that was common both for physical differences and social reasons. So you got to think that, you know, you could have perhaps hybrids being created, but if those hybrids do not breed back into the parent populations, because they look a bit different to normal, their combination [of] features, those genes will never penetrate the parent populations.

Steve: And that's, there are two different issues: Whether or not there was intermixing, that could have happened without a genetic legacy being passed on but ...

Stringer: Yeah, there could be contact, but ...

Steve: What we are talking about is, are their individuals alive today who carry Neandertal genes—did that lineage survive? Whether or not, you know, some Neandertal guy and Homo sapiens woman got together without leaving progeny—we can never know.

Stringer: Well, yes. I mean, you are right to separate those issues and there are some people who, my good friend, Erik Trinkaus, for example, thinks he can see in the early modern record, evidence of some Neandertal features showing up in odd places in the fossil record of the Cro-Magnons; and he says that's evidence of a phase of interbreeding. And then I would say, "Well, okay those might be rare events, [but] it can't be too rare if they are showing [up in] fossils." I don't agree with the interpretation, I have to say, with Erik. I don't think necessarily these features are coming from Neandertals. They are probably the variation of modern humans and some of them are archaic features that could be retained from ancestors in Africa. They don't have to come from Neandertals, so that's one issue. But even allowing that there could be such hybrids and that there was a low level of contact as I had mentioned there were huge populations crashes in Europe around the peak of the last ice age. Some people estimate may be 75 or 90 percent of Europeans died out at the peak of the last ice age as we retreated to refug[ia]. So imagine a small bit of Neandertal DNA in those populations before the maximum and then you lose most of those people—you could easily lose [a little] Neandertal contribution in such a population crash. So even if a little bit was there before then it doesn't get through and the genome work so far suggests that even that little bit is not there, at least in these Neandertals as far as we can tell from Pääbo's announcement so far. He does not see evidence. This is a female Neandertal from India that gives most of the genome data, that's in a sense you would expect the female Neandertals to be showing signs of interbreeding more probably than the males do, if it is an asymmetric pattern. [It's dangerous to] make modern metaphors but if you look at colonial metaphors, when European travelers went to the Americas and to Australia, the gene flow tended to be more into the native groups than the other way around. So by analogy of that we would expect the female Neandertal to be the most likely price to be looking for signs of gene flow, and it does not seem to be there so far. But you never know, and I think we will agree that you need more samples; you can't base this on just a small sample—we need more Neandertals and obviously [Svante is] working on enlarging the sample. What's incredible is that even in the Neandertal sample we have got, for some reason these Vendia remains, some of them, have many times better preservation of DNA than other specimens, and no one can say why that is. It's just chance events—even on the same bone, if you drill into some places you will find huge differences in the amount of DNA. So basically he has got to just spread his net as widely as possibly and then try and pick up these chance remarkable preservations. And, of course, we really need to have DNA from Neandertals over in Siberia. More of that we know they seemed to get that far, so what were they like compared with the ones in Western Europe. Hopefully, eventually there'll be a whole genome data from those, and although unfortunately because of preservation conditions we are unlikely to get good DNA from tropical/subtropical Africa where our species originated, nevertheless, possibly in high-altitude caves in North Africa and South Africa there might be better DNA survival and certainly in places like China and Siberia, Mongolia, there are human fossils, there are like archaic people in China comparable to the Neandertals, those will be good candidates to look for ancient DNA as well and that would be very exciting because then we have got whole different bit possibly of the human lineage with DNA. And then there is the Hobbit, of course, in Flores, whatever that is, the conditions there are poor for DNA preservation but it would be absolutely remarkable if DNA can be recovered from Homo floresiensis because that could be an even older branch of the human tree.

Steve: This is a really remarkable times to be a Neandertal researcher.

Stringer: Absolutely, yeah. I mean, I would say the whole last 30 years have been remarkable times because so many new techniques have come online: dating, CT studies, the synchrotron, allowing us to look [at] individual growth lines in Neandertal teeth, ...the ability to date things with much greater precision, and then DNA—and, you know, I was in Svante Pääbo's press conference in London in 1997 when [he] announced the first mitochondrial DNA and I went on record saying it was the equivalent in paleontology if landing something or landing on Mars and who could have imagined 10 years later we talk about the whole genome; it's incredible.

Steve: Kate Wong is Scientific American's go to person on human evolution. She is also the coauthor of the new book Lucy's Legacy: The Quest for Human Origins with the discoverer of the world famous Australopithecus skeleton known as Lucy, Donald Johanson. The title is Lucy's Legacy. What is Lucy's legacy?

Wong: It means a number of things. First of all, when Johanson and Tom Gray discovered Lucy in 1974, it prompted a decades long search for more information about her species, Australopithecus afarensis, that continues to this day and since then our researchers have unearthed an enormous amount of information about who Lucy was, who her species was, where it lived, how it behaved; and so that's one aspect of Lucy's legacy.

Steve: Because we now have something like 360 specimens of afarensis.

Wong: Yeah, at last count there are 365 individuals represented by the fossils that have been collected of the species. Many of them are very fragmentary but others are more complete, such as Lucy, and then there are of course there are other individuals that are represented by largely complete skulls and other material, as well.

Steve: You know, we should probably back up because we both live in a world where there wasn't Lucy and then there was Lucy. You were a little kid but ...

Wong: ... I was just born.

Steve: Alright, so look, I mean take it back—I live in a world where there wasn't Lucy and then there was Lucy. But, you know, a lot of people listening have grown up where there was always the Lucy fossil, it's the most famous human ancestor fossil in the world.

Wong: It is and that's partially because she is so complete and then she also—when she was discovered, answered a longstanding question about human evolution, which was, "Which of the two of our most salient features, upright walking or large brains, came first?" And Lucy showed without a doubt that upright walking preceded the evolution of large brain size.

Steve: So before Lucy it just wasn't clear which came first, the upright walking or the big brain, and Lucy decided it definitively.

Wong: That's right. She decided it definitively because it's absolutely clear from her pelvis and other features that she walked upright on two legs just like we do and yet her brain is no larger than a chimpanzee's brain.

Steve: 3.2 million years ago?

Wong: Yes, Lucy is 3.2 million years old, although her species has been found spanning a period of about 500,000 years.

Steve: The subtitle of the book Lucy's Legacy is The Quest for Human Origins and the book is as much a scientific evocation as it is sort of an adventure story.

Wong: Yeah, what we did in the book is to both recount what Johanson and his colleagues have been doing at Hadar—and the work still continues there—since 1990, you know, unearthing [clues] about Lucy's species; but then, of course, when Lucy was found and analyzed she instantly begged the question of, "Well what came before her?" And although she was among the oldest hominids known when she was discovered, there are now putative human ancestors dating back as far as seven million years ago.

Steve: Do chimps and humans have those as a common ancestor then?

Wong: No, those are not the remains so far as we know of the last common ancestor of chimpanzees and humans but they get that pretty close to where we think that last common ancestor was.

Steve: You know, there is the traveling exhibit where the actual fossil remains of Lucy are going around the country and that's in New York for the next couple of weeks, and I actually went to see it Friday night and it's an amazing thing to see because those are really her bones, you know, and she is small. People might not realize how little Australopithecus afarensis is. She was what, about three feet tall?

Wong: Yeah, probably about a meter tall but also probably fairly muscular.

Steve: But she also kind of filled me with pity, actually, just to think about her actual life and how difficult it must have been. There is this little, sort of, human just with nothing that we take for granted everyday—no clothing, no fire, no walk to the supermarket to get any food, I mean, every minute must have just been a hardship to live through, and that's where we all come from. We come from the survivors of all those hardships. So Lucy's legacy, I mean, we are Lucy's legacy.

Wong: We are Lucy's legacy. You know, Lucy is believed to be ancestral to all of the later Australopithecines species and also our own genus Homo which includes everything from us to Neandertals, to the little Hobbits of Flores and, you know, we cover all of this in the book, and it's just incredible to see how much new information about all of Lucy's descendants has been uncovered in the past couple of decades, truly an astonishing period for paleoanthropology.

Steve: So how did you actually come to be to Johanson's coauthor on the book?

Wong: Well, he and his agent were familiar with my work at Scientific American, where I have contributed a number of articles on human evolution and they approached me and asked me if I would be interested in collaborating on the project.

Steve: There is a story in the book about him going back to Ethiopia after many years—the political climate there made it impossible for Johanson to do any field work in Ethiopia for a while—and when he got back and announced to the customs official that he was the discoverer of Lucy, that was like a really big deal. So Lucy is a huge deal in Ethiopia where she was discovered.

Wong: Absolutely. Ethiopians really have a huge appreciation of this incredible fossil that comes from their country. And it's not just Lucy, of course; there have been a number of really important discoveries of human fossils in Ethiopia, the most recent of which—the most recently described of which—is of course the Ardipithecus fossil that was unveiled last week.

Steve: And what's the big deal about that fossil?

Wong: Well, Ardipithecus comes from a slice of time in human evolution that was very poorly understood. I alluded earlier to some putative hominin remains dating back as far as seven million years but those were only known from a skull in one case and some teeth and limb bones in another case, and Ardipithecus is a partial skeleton with many, many, many bones preserved. Actually there are approximately 36 individuals represented by all of the Ardipithecus finds but the main find is a largely complete skeleton. What's really interesting about Ardipithecus is just how much more primitive it is than Lucy and other Australopithecine fossils. It is clear from the pelvis that Ardipithecus was capable of walking around upright but it also has a number of primitive features that indicate that it climbed on the trees, as well.

Steve: So the Ardipithecus—the way it moved is really interesting and there are some other aspects that we know about its behavior based on its physiology; well not physiology but anatomy.

Wong: Yes, apparently Ardipithecus had small canine teeth. It's interesting because it gives us a potential insight into the behavior of the species, and that's because in chimps and gorillas, for example, the males have these large, slashing, daggerlike canines, and they use them both for fighting and in aggression displays when they are competing for females. Ardipithecus however—the males and the females have pretty similar canines, and they are small. There wasn't as much sexual dimorphism in Ardipithecus, which is to say there were fewer differences between males and females. This was reflected not only in the teeth but also in the body size. Males and females of Ardipithecus seemed to have overlapped a lot in body size, and what this suggests is that females were not selecting the biggest, most-aggressive males to [mate] with. One of the points that is underscored by the Ardipithecus discovery is that the last common ancestor of humans and chimpanzees did not look particularly like a chimpanzee, which is what some paleoanthropologists had speculated. The researchers who described Ardipithecus argue that their discovery strongly implies that humans never went through a knuckle-walking phase over the course of evolution which is something that paleoanthropologists have been debating for a quite sometime.

Steve: So in your lifetime there is Lucy, there is Ardipithecus, there is the Hobbit, which we were calling, what's the official Latin name again for the Hobbit?

Wong: Homo floresiensis.

Steve: Because it is from the tiny island of Flores. So the world of paleoanthropology, the search for human fossil remains—it is like harder than ever right now.

Wong: It is a really exciting time to be covering this field, especially with the discovery of the so-called Hobbits from Flores, the island of Flores and Indonesia. This is a find that really changes a lot of what paleoanthropologists thought they knew about human evolution and it['s] shake-ups like these that are the really thrilling things to cover as a journalist and, in fact, in the November issue, I have an article that talks about some of the most recent discoveries that have [been] made about the Hobbits since they were first analyzed in 2004.

Steve: To hear an interview with Donald Johanson, check out the Science Talk podcast episode of September 20th, 2006, available in our archives at www.SciAm.com/podcast or directly at www.snipurl.com/lucyfinder

Now it's time to play TOTALLY....... Y BOGUS. Here are four science stories, but only three are true. See if you know which story is TOTALL....... Y BOGUS.

Story number 1: Catnip chemicals discourage flies that annoy cows.

Story number 2: A home run by Yankee first baseman, Mark Teixeira in the first round of the play offs against the Twins left the ballpark in just 2.88 seconds, making it the fastest homer of the year.

Story number 3: Our biggest defense against fungal infections appears to be our ability to move which limits spores' ability to gain a foothold, or whatever kind of hold a footless [spore]gets.

And story number 4: Election outcomes affect men's testosterone levels.

We'll be back with the answer, but first, I want to thank all the listeners who wrote in about last week's episode. We had mentioned a century-old Scientific American item suggesting that images be put on the walls of subway lines so that the effect for the rider would be movies to watch. Numerous people wrote into point out that such images actually do exist today in subway lines around the world; they are mostly ads but they are fun. Check out the comments on the October 14th podcast. You will find links to see the videos. You can find the October 14th Science Talk page at www.SciAm.com/podcast

Time is up.

Story number 1 is true. USDA scientists have identified two chemical compounds found in catnip that stable flies really hate. The compounds stops most flies from biting cattle and also keeps most females from laying eggs. It's estimated that stable flies [cost] the U.S. cattle industry two billion dollars annually in reduced milk yield and other production losses. The research will appear in an upcoming issue of the Journal of Medical and Veterinary Entomology.

Story number 2 is true. Teixeira's 2.88-second homer went out faster than any other of the over 5,000 major league home runs of 2009. That's according to the Web site www.hittrackeronline.com. If you are a baseball fan do not go to that Web site, because you will be there for the rest of the day.

Story number 4 is true. Election outcomes did affect men's testosterone levels according to research done last fall. A study of 163 college-aged men found that Obama voters maintained stable testosterone levels while McCain voters saw their levels drop after the results were announced. For more information check out the October 23rd article on our Web site called "Jock the Vote: Election Outcomes Affect Testosterone Levels in Men".

All of which means that story number 3 about locomotion being the biggest reason we avoid most fungal infections is TOTALL....... Y BOGUS. Because a new study finds that it's our body temperature that keeps us from being widely colonized by fungi. Most fungi do quite well up to about 86 degrees but survivors dropped 6 percent for every additional degree, so just being at 98.6 degrees renders most fungal species, well, dead. The study appears in the Journal of Infectious Diseases. For more check out the October 23rd episode of the daily Scientific American podcast, 60-Second Science.

Well that's it for this episode of Science Talk. Check out www.ScientificAmerican.com for the latest science news and our in-depth report about Galileo and the International Year of Astronomy. For Science Talk, the podcast of Scientific American, I am Steve Mirsky as [is] my Twitter handle. Thanks for clicking on us.