Science Talk

When Humans Almost Died Out; Earthy Exoplanets; And Scientific American's 165th Birthday

Podcast host Steve Mirsky talks with human evolution expert Kate Wong about the small group of humans who survived tough times beginning about 195,000 years ago and gave rise to all of us, a story told in the cover article of the August issue of Scientific American, our 165th anniversary edition. And Editor in Chief Mariette DiChristina talks about the rest of the contents of the issue, including our coverage of the search for rocky exoplanets. Plus, we test your knowledge about some recent science in the news. Web sites related to content of this podcast include

Podcast host Steve Mirsky (pictured) talks with human evolution expert Kate Wong about the small group of humans who survived tough times beginning about 195,000 years ago and gave rise to all of us, a story told in the cover article of the August issue of Scientific American, our 165th anniversary. And Editor in Chief Mariette DiChristina talks about the rest of the contents of the issue, including our coverage of the search for rocky exoplanets. Plus, we test your knowledge about some recent science in the news. Web sites related to content of this podcast include

Podcast Transcription

Steve:          Welcome to Science Talk, the weekly podcast of Scientific American posted on August 12th, 2010. I'm Steve Mirsky. This week on the podcast

Wong:          Starting around a 195,000 years ago and kind of lasting up to 123,000 years ago, the planet entered into a glacial phase; kind of everything went to hell in a handbasket, except for [in] a few little pockets.

Steve:          That's Kate Wong, our resident expert in human evolution. She'll be talking about the cover story of the August issue of Scientific American "When the Sea Saved Humanity", and one of those little pockets that may be the reason our species survived. And Editor in Chief Mariette DiChristina talks about the rest of the contents of the August issue. I started off talking to Mariette.

Steve:          So apparently, we're lucky to be here today; we three and the other almost seven billion others on Earth?

DiChristina:         It's hard to believe isn't it that with almost seven billion people on Earth and many millions of them living right here with us in New York City, that once upon a time human beings were almost extinct.

Steve:          Once upon a time being approximately how long ago?

Wong:          So, Homo sapiens evolved a little bit for about 195,000 years ago and things were going along pretty well up until that point. There was adequate food, the climate changes were mild and all of the plants and animals that Homo sapiens made a living eating were flourishing.

Steve:          I think the article says, "Life was good."

Wong:          Yeah, life was good. Exactly. And then starting around 195,000 years ago, and kind of lasting up to 123,000 years ago, the planet entered into a glacial phase. And what this meant in Africa—which is the only place that Homo sapiens lived really until about 50,000 years ago—is that, kind of, everything went to hell in a handbasket, except for a few little pockets on the continent, which [were] pretty much the only options for survival. And one of those places was particularly special, which is the southern coast of Africa, where there was an incredible diversity of plants that have underground storage organs that contain really high-quality carbohydrates. In addition to that, along that coast there's a combination of warm and cold currents that foster a diversity of shellfish that offer a very high-quality protein. So, between the high-quality carbohydrates from the tubers and the protein from the shellfish, humans living there would have had it made.

Steve:          So your diet basically consists of potatoes and mussels, or the Neolithic versions of those things.

Wong:          Exactly.

Steve:          But it's a good diet, it's filled with, as you said, carbohydrates and, but also not too much fiber so that it's easily digestible, especially for children; and apparently our best estimates are that the population had gotten down to maybe just a couple of hundred breeding couples of Homo sapiens?

Wong:          Yeah, the estimate is really different depending on the genetic study, but some of them have put it at about a few hundred, maybe even just 600 breeding individuals in the population.

Steve:          And the fact of our low genetic diversity indicates that relatively recently in evolutionary time, there was this bottleneck of very few breeding couples.

Wong:          Exactly. And the estimates from the geneticists are that whereas the breeding size, the breeding population had numbered around 10,000 individuals prior to this catastrophic climate event, it then, that event then whittled the number of breeding individuals down to possibly maybe even just 600 people.

Steve:          The article also talks about some fascinating evidence for technology that's apparently tens of thousands of years older than anybody ever thought before  —the heat treatment of the stone tools.

Wong:          One of the most incredible discoveries to come out of this particular site that the article focuses on, which is just called cave PP13B found in Pinnacle Point on the southern coast of Africa, is that people seem to have been taking a raw material, a stone called silcrete, and subjecting it to heat treatment in order to be able to make these very [finely] wrought small stone blades that they could then fix to a shaft of wood and turn into some sort of projectile weapon. And, you know, previously archaeologists had found, they noticed a discrepancy between the nature of the [silcrete] in the stone tools that was turning up. They were turning up at sites, and the raw material that they found lying around the landscape and what they were able to show experimentally, is that the people of PP13B were probably heating the stone in a very specific way, an elaborate way that involved burying it under a certain amount of sand and removing it from the heat at a certain point to avoid making the material brittle. And this is all technology that was believed to have originated in France only perhaps 20,000 years ago, and the discoveries at PP13B indicate that people were using this incredibly sophisticated technology up to 164,000 years [ago].

Steve:          And the implication of that is if you're going to do that kind of complex work, there's probably language so that people can communicate with each other about what step they [have] to do next; and our cognitive abilities were probably pretty well advanced at that point.

Wong:          Yeah, there's been the sort of longstanding idea in archaeology that somehow even though Homo sapiens are [a] species that evolved 195, 000 years ago, that somehow we didn't become behaviorally modern, people didn't start thinking like us until maybe around 40,000 years ago. And that thinking was based in large part on the archaeological record that we see on France, where you see the famous cave paintings and very elaborate tools made of bone and other materials. And what people have been finding over the past decade or so is increasing evidence that humans were in fact exhibiting lots of indicators of what we call modern human behavior well before those Europeans. And now with the discovery of the heat treatment of stone tools at PP13B, as well as other indications of modern thinking like the fact that they've found great quantities of ground-up red ocher which is believed to have been used as body paint or makeup. In addition to that, certain kinds of shells that were obviously collected just for their aesthetic appeal as opposed to for any food they contain because by the time they washed ashore they wouldn't have actually had any meat in them still. So they [were] just collect[ed] for beauty. These are all signs that people were really thinking like us much, much earlier than previously thought and probably [were] cognitively modern at the same time that they became physically modern.

Steve:          And there's probably a lot more evidence for this kind of society way back when in southern Africa, but unfortunately it's underwater right now.

Wong:          Yeah, the discoveries in this region, this particular cave PP13B is located in a cave, that's kind of carved out of a cliff face that's well above the modern sea level. But below the cliff, there's a very shallow bank that extends for many kilometers out into the ocean and when the climate was changing, the sea level, even if it declined just by a little bit, that would have created a huge distance between where the cave is located today and where the water was. So what this all means is that, probably there's lot of archaeological sites on this bank but it's now covered over with water.

Steve:          And there's a terrific photograph of the cave in question, in which you can clearly see this really rickety staircase that apparently, the article says, a local ostrich farmer built for the archaeologists so they didn't have to scale the cliff face every time they wanted to get in there.

Wong:          Yeah, the whole way that Curtis Marean and his colleagues discovered this cave is really interesting. They knew that they had to find a locality that was today located at least 15 meters above sea level, because otherwise, because in the past the sea level was higher, it would have probably washed out any archaeological remains from any site located lower than that. So, they were looking at pictures of this coastline and they saw the caves located in these cliffs, and they thought, "Wow! That might be a good place to look. So they, you know, put on their gear and went scrambling down the cliffside and found the cave. But of course scrambling down the cliffside isn't a very safe thing to do. So, they hired this local ostrich farmer to build down the staircase so they could conduct routine excavation of the site.

Steve:          Pretty cool. And we have an interactive Web feature that goes along with this article.

Wong:          We do and there are lots of great videos of the author talking about the discoveries and one of his colleagues showing how the stone tools are made and talking about that heat treatment, and there's also an interactive feature where you can see how the coastline is changed over time.

Steve:          In fact, let's listen to a short clip from the video of Curtis Marean, the author of the piece.

Marean:          There are two major results that we've published in the last couple of years from Pinnacle Point. The first one that was published in 2007 in Nature was so far the earliest evidence that we have anywhere in the world for people exploiting shellfish from marine locations. And along with that what we found is that people were using ocher. There are clear indications that they were grinding the ocher, probably to produce powder, which they would then use for painting either their bodies or painting rock paintings. And the other thing is that we found they were producing very small tools that we call bladelets. Usually, when we find bladelets and assemble it, it just means that people were melting them and producing complex tools. And then the second major result that we published, just in 2009 in Science, we discovered that people at Pinnacle Point and at, almost certainly, at other sites in coastal South Africa were taking a rock called silcrete, which occurs naturally there, but in its natural [state is] not a particularly good stone for flaking. And what they were doing is they were intentionally heating it, what we call heat treatment, and that significantly improves its ability to be flaked. We found that people were using that technology as their main technology for stone tool manufacture, at least by 71,000 years ago, and they were using it occasionally all the way back to a 164,000 years ago, and the earliest prior evidence for that heat treatment technology was about 20,000 years ago in France.

Steve:          So that's the article, the cover article for the August issue of Scientific American, "Secrets of Our Success", and Kate, thanks a lot.

Wong:          You're welcome.

Steve:          So Mariette, right next to, right in front of this article about our bottleneck in the past is this short section, [this] little collection of origins. [Why don't you] tell us about that?

DiChristina:         Right. So we created a theme package with origins in this issue because although humans—although our lineage I should say—arose much earlier than this human bottleneck that we were just talking about, in many ways, it's the origin of our modern humanity. And likewise last year, we did a whole single topic issue on origins of various things. In fact we had 57 different origin stories and then another dozen or so neat stories online. So this year we thought a reprise might be fun. In a short section that is a companion to this story that is the cover, "Secrets of Our Success", and we have little articles on things such as, how did families arise? Or human morality? Or influenza? And…

Steve:          Swiss cheese!

DiChristina:         Swiss cheese! Which is one of my favorites, both enjoy the history of it and the flavor.

Steve:          Oh yeah, me, too.

DiChristina:         And timed with that, why this origin is perfectly timed for Scientific American, is of course, we're celebrating our own origins this issue—165 years. Scientific American, happy birthday to you!

Steve:          August 1845 we rolled it out.

DiChristina:         In those days, in a weekly newspaper, you know, a broadsheet sort of publication with lots of stories about science and technology of the era.

Steve:          And although we don't have those really, really old ones available yet in our digital archive, if you go to Project Gutenberg, on the Web, you will find many of the older issues, certainly ones dating back to the 1870s and 1880s. That's how I discovered, purely by accident, that Mark Twain had written for us once.

DiChristina:         If you also Google something called "19th century Scientific American", you'll come up with many articles, doesn't look like the old issues, but the type is there. And I think it is Cornell University also that is involved with an archiving project for this magazine and others from the 1800s. So if you google "Scientific American, Cornell" I think that will pop up as well. But in this issue, we have some samplers from our lovely 50 and 100 and 150 years ago section this year; this month, rather, we have expanded it to 50, 100, 150 and 165 years ago in Scientific American.

Steve:          And we'll get to that.

DiChristina:         There's a little section on that in the online, a little bit more material.

Steve:          So, before we get to that, let's talk a little bit about another one of the articles in this issue, about Earth-like planets elsewhere out there. And it's such a fascinating subject because, you know, up until in our lifetimes there was no way to know whether any other stars had any planets, and now we know that there are at least, you know, a few hundred exoplanets we call them, out there and we now have this new missions that's been sent up. We have photographs of the space telescope in the article—looks like somebody's golf car that they're walking the fairway with—but it's out there looking for other planets and also planets that could be Earth-like planets that are not just gas giants like Jupiter, but would be rocky planets that might have the conditions for life.

DiChristina:         Let's talk about the challenge of finding planets, just back, to back up for just a minute here. So I remember some years ago, when we first started finding planets, in fact the first ones were found around something called [a] pulsar which is a half dead star that['s] sort of radiating material on a timed basis, and there [were] some planets found around them years ago. [And] we thought, "Well that's really interesting as an object in the cosmos but it doesn't really tell us that much about planets like ours and how did our own solar system evolve." I mean, this was such a different system. And then as telescopes improved, we started to find very, very large planets—you mentioned gas giants, such as Jupiter. Jupiter has something like 300 times the mass of Earth, and when we speak of Jupiter-like planets that are found around other stars, which were found before the Earth-like ones I'm going to tell you about in a just a minute, these were multiple times the size of Jupiter.

Steve:          Yeah, they're gigantic.

DiChristina:         Gigantic and then in very, very close orbits typically to their stars; again not that this mean that that's the kind of planets that are out there. [It's] sort of the limitations of our telescopes at that time. We were only able to find these because they're quite large, and the effects that they have on their stars are more obvious and that's easier to see.

Steve:          They might make an orbit of their sun, one of these gas giants, in just a few days.

DiChristina:         Right. I mean, really very fast and then with this new instrument called Kepler, which was up in 2009, we've now found hundreds of candidate planets, and indeed there are many dozens of candidate Earth-like planets. And when we speak of Earth-like planets, what we mean here is not that Jupiter like gas giants, but rocky bodies that are more like the planet we're so happy to call home. And also within just a few times the size of Earth; so let's say four times the size of Earth or six times the size of Earth, quite different from these things that are multiple times the size of Jupiter. And that's really intriguing because now we can begin to see not just how planets evolve in other places, but how are they like or not like the one that we live on.

Steve:          Now the telescope can't really see one of these other planets. What it can see is the effect that the planet would have on the star.

DiChristina:         Right, you're right. There are two kinds of effects. One is called the wobble effect. So, if you could imagine, or just like, imagine you and a friend holding hands and then your friend helps you, sort of, helps you swing around a little bit and you would pull your friend back and forth a little bit as you circle him or her. In just the same way, the planet that is orbiting a star has a gravitational effect on that star and it causes the star to wobble a little bit, and this indirect evidence is what's picked up by telescope. That's called the wobble method, kind of creative. And then there's another method, which is where the planet crosses in front of the star, between you and the star. So, if you can imagine holding a flashlight facing your face and you stick your hand in front of that flashlight, you will dim the flashlight's light a little bit. In just the same way, when a planet goes in front of the star and when we're watching, we can see the brightness of that star dim a little bit. The amount of that brightness dimming can give you a sense of how large the planet is.

Steve:          Right and when you combine the two, and you get the size based on the dimness impact and the wobble, which gives you some indication of the mass, then you can figure out the density. Because that's what those two things together would give you and then you can know whether it's a gaseous planet or a solid planet.

DiChristina:         Right, now you're really talking. Once you get the mass and composition, you can start to make some pretty good educated guesses about what that planet might be like.

Steve:          Now you're cookin' with rock.

DiChristina:         Now you're cookin' with rock. So there're a couple of kinds of these Earth-like planets that we found. We could start with our own just to, kind of, set the scene. It's a rocky body, right, and it has a certain amount of, because of those, the rocky shape and the movement that we have, we have plate tectonics, we get volcanic activity and the planet is fairly active, you know, meaning that the surface changes over time. If you have it—and we forgot to say, Steve, that these are called super-Earths because they're a little bit bigger, these exoplanets or extrasolar planets as they're also known. If you have an iron-and-rock super-Earth, the effect, the geological effect might be a little different. First of all, it would have a little bit more heat from radioactivity and thus the convection or the movement of that heat through the body would be much faster—in fact maybe up to 10 times faster than it runs through Earth's material—and you might have plates on the top, like we have tectonic plates that form our continents. Ours are very thick and they can build up over time, but with that faster convection, those plates are moving around faster on a super-Earth and they're thinner. So they, you can begin to imagine what that might look like or might act like. Also the size of that iron-and-rock super-Earth means that it's iron core would be solid unlike our iron core, Earth's iron core, which is liquid and thus because it's liquid it can create a geomagnetic field that would not be true on an iron-and-rock super-Earth.

Steve:          So how would the birds navigate on that other planet?

DiChristina:         [They] may have very interesting new navigational systems, for all we know.

Steve:          And because you would have plate tectonics, you'd have mountains, but the mountains would probably not be anywhere near as high as the mountains are on Earth. The highest mountain in the solar system is on Mars, which is even smaller than the Earth, and that makes sense because of the plate tectonics of all those different bodies.

DiChristina:         Right—and we forgot to acknowledge it although it's implicit—that when you have a super-Earth [that's] multiple times the size of Earth, it has more gravity. So those mountains have a harder time getting high, or you know, they would tend to probably grow faster and erode faster than the mountains that we have here on Earth. There's another kind of super-Earth, and this is the super-Earth that isn't an iron–rock Earth-like Earth, but a water-iron-and-rock super-Earth. And here you might think of it as ocean world. In this case, instead of one solid mantel that we described for this super-Earth that's an iron-and-rock super-Earth, they would be two solid mantels. One would be a rocky core and the other one right around it would be an ice core, so it will be solid at the bottom of a sea of some, you know, water or liquid that would be hundreds of kilometers deep. So anyway, it's fun to try to imagine what these are even though we can't see them. Based on their physics and geophysics that we can understand, we can kind of paint a little bit of a picture of what these other places in the cosmos might be like.

Steve:          And the Kepler is just beginning to feed us back data, so over the next few years we should learn a lot more about exoplanets and Earth-like exoplanets.

DiChristina:         Yeah, let me tell you just one two more quick things about that. First of all, I forgot to say that Kepler's job is to stare at 150,000 stars at all time, looking for those wobble and dimness signals that we talked about just a little while ago; and right, it's just been up fairly recently, very excited to see the results that are going to be coming. After the Kepler, and maybe while the Kepler is still up, in fact, I think they will overlap, the successor to the Hubble space telescope, the James Webb Space telescope, will be going up and it will have the additional capability of not just finding evidence for those planets. So, the planets that Kepler has found, the James Webb Telescope could then look at for atmospheric composition and then you can begin to add yet another aspect of the picture of these foreign worlds.

Steve:          Right, if you see a lot of particulate pollution, you might …

DiChristina:         You might suspect humans.

Steve:          Right. Lot of other interesting pieces in this issue about pills that you can swallow that have video capability. I mean, that's already being used in some cases, but these would be more advanced.

DiChristina:         Right. If I could just say it really quickly, to that one, so since about 1999 or so there had been capsules that people could swallow that take pictures through your body. It's called capsule endoscopy. And now the latest thing with that is obviously, it's very handy to be able to swallow a capsule and take pictures but it's passive. It's passing through your body at some certain rate of speed; you can't say, "Well wait a minute, what was that? Back up and shoot another one." You just get what you get, so the latest effort with [these] pills is to try to make them have some kind of motion, and they could get around the body with little foot-like or claw-like devices, appendages on the end of them. They might use a propeller, some means of locomotion, and they have to be able to both take instructions so if you wanted to back it up and look at some thing again it could happen and also convey information and data and images at a high rate of speed.

Steve:          So we have that to look forward to.

DiChristina:         So we have that to look forward to.

Steve:          Excellent.

DiChristina:         All in the size of something that would be about the size of a gummy [bear] that you can swallow, which presents a lot of interesting technology challenges.

Steve:          Yes, especially in the retrieval phase. But, well let them figure that out on their own. Let's talk just real briefly about, you know, we always have the 50, 100 and 150 years ago, as you said, but [we have] the additional 165 years ago in this issue to celebrate our anniversary and let's see what we were talking about in August 1845. We [have] a little item about Morse's Telegraph, which was all the rage. It was the Internet of its day what, not even the Internet, it was the iPhone 4 of its day.

"This wonder of the age which has for several months past been in operation between Washington and Baltimore appears likely to come into general use through the length and breadth of our land. It is contemplated by the merchants of our Western states to communicate their orders for goods etcetera, by means of the telegraph instead of abiding the slow and tedious progress of railroad cars." Railroad cars of course being the dial-up modems of the day.

DiChristina:         That's, first of all that's one of my favorite quotes from that whole issue, so I am glad that we picked that one up. I love the idea of the [editors] saying it appears likely, you know.

Steve:          Right.

DiChristina:         [As if] there were some doubt, and also that it is the wonder of the age. The front page of that particular issue has a lovely picture of railroad cars, and this new technology advance [is] trying to make them, although they don't quite use this term, they're trying to make them more aerodynamically efficient. But so even in those days, the data moved to[o] slowly for us. We couldn't get enough broadband.

Steve:          And we're trying also to save on our energy resources.

DiChristina:         Yeah, it's just amazing.

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

Story 1: A lobster caught off Rhode Island was kept [from] the hotpot by its rare coloration.

Story 2: June 2010 was the warmest June on record.

Story 3: A canvas umbrella at the beach not only blocks the sun, if you're under it, you actually also get appreciably less exposure to ocean viruses carried out of the ocean by surface wind as the viruses settle back down.

And story 4: The World Health Organization projects traffic fatalities to be the third leading cause of mortality worldwide by 2020.

Time's up. Story 4 is true. The World Health Organization does project traffic fatalities to be the third leading cause of mortality in just 10 years. One way to lower the risk is to have us not drive cars and one way for us not to drive is for the cars to drive themselves. To that end, in September a driverless Audi TTS will drive at highway speeds to the top of Pike's Peak. Well it will start out anyway. For more check out the article on our Web site called Automatic Auto, a car that drives itself.

Story 1 is true; a lobster found in Rhode Island's Narragansett Bay is yellow and gold in color, which kept it from being boiled. Such coloring is found on an estimated one out of every 30 million lobsters. Google "yellow lobster" to see a photo. The golden boy will be on display at the University of Rhode Island's Bay campus aquarium.

And story 2 is true. June was indeed the warmest June on record. That's according to NOAA, the National Oceanic and Atmospheric Administration. They also noted that the April-through-June period average and the January-through-June period average were also the warmest on record. They say that the analysis from the National Climatic Data Center is part of a suite of climate services NOAA provides to government, business and community leaders so that they can make informed decisions or in the case of governments, so they can not do anything.

All of which means that story 3, about beach umbrellas intercepting ocean viruses is TOTALL……. Y BOGUS. But what is true is that canvas umbrellas at the beach would do a pretty good job doing their actual job blocking the sun. However, they still only keep about two-thirds of UV rays from reaching anybody under them because so much UV bounces off other surfaces and sneaks in from the sides. The canvas itself stops about 95 percent of the UV according to the study in the Journal Photochemistry and Photobiology. The research was done at the University of Valencia, where everybody who graduates gets a UV degree.


Steve:          Well that's it for this episode. Get your science news at You can check out the interactive feature "When the Sea Saved Humanity"related to the cover story in the August issue of the magazine, and you can read about the car that will drive itself to the top of Pikes Peak or bust, presumably. Follow us on Twitter, where you'll get a tweet every time a new article hits the Web site, our Twitter name is @SciAm—S-C-I-A-M For Science Talk, the podcast of Scientific American, I am Steve Mirsky. Thanks for clicking on us.

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