Science: The Demise of the Woolly Mammoth

Washington Post staff writer Christopher Lee was online Monday, June 11 at 1 p.m. ET to discuss his Monday Science Page story about new theories as to what killed off the woolly mammoths.

Read the story: New Theory on Old Debate: Comet Killed the Mammoth (Post, June 11).

The transcript follows.

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Christopher Lee: Welcome everyone. We're going to chat -- or try to anyway -- about what some of the latest scientific research suggests about the extinction of the woolly mammoth more than 10,000 years ago.

Until now there have been two competing prevailing theories -- that humans hunted the beasts to extinction or that the end of the last Ice Age spelled the mammoth's doom. Last month, though, a group of scientits presented new findings that a comet may have exploded over North America some 12,900 years ago, wiping out the mammoth and lots of other big animals. Still other researchers, in Britain this time, have recently published research showing that there were at least two genetically distinct groups of mammoths ages ago, and that one line died off around 40,000 years ago. They say this illustrates that extinction of a species seldom occurs with one sweeping event, that the table was being set for the mammoth's extinction a long time before the species actually died off.

Me, I usually cover government and politics, but I find this stuff fascinating. I can't provide much in the way of new information about the science here -- what you've read in the story is what I know -- but I'm happy to chat about the experience of reporting this story. Let's begin.

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Charlottesville, Va.: Christopher,

Do those scientists who advocate for the theory that early humans killed off the mammoths tend to much about actual hunting? Having read a great deal about the hunting of elephants in Africa and the difficultly that was involved with that even using modern firearms, it seems impossible to me that an entire species of elephants could be hunted to extinction using only primitive weapons, especially on open grasslands with little or no cover. One could only drive but so many of them off of cliffs before animals so intelligent got wise to it. Meanwhile, there was certainly easier, less dangerous prey around. Your theory, while I'm not yet totally convinced of it, makes a lot more sense than the 'hunted to extinction' notion. I am wondering whether you see these same practical holes in that theory and whether this was part of what led you to look elsewhere for the truth.

Christopher Lee: Again, I'm a layman, but my understanding is that the argument in favor of humans killing of the mammoth is that the animals lived from about 2 million years ago to about 10,000 years ago and somehow made it through various cycles of global warming. The big difference, toward the end, was the rise of the human population in North America and, in particular, the advent of "advanced" stone weapons, such as Clovis spearpoints, that made the humans much more deadly. And it wouldn't take long for an animal unaccustomed to human threats to perish under the spear, so to speak. Just look at the havoc humans wreaked on the Galapagos Islands among species that lived for years without having to fear human predators. On the other hand, some scientists, like you, find it hard to believe that humans could have wiped out the mammoth simply by hunting them. After all, one said, there aren't that many people living in Northeastern Siberia today. Back then,there were very few.

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Washington, D.C.: Thanks for taking my question. Is there any chance of recovering enough good quality DNA to actually clone a mammoth, with an elephant as host mother?

Christopher Lee: You raise a very interesting question. The short answer is that I don't know. But in reporting this story, I did come across some old news clippings from a couple of years ago that discussed what DNA research had shown about the mammoth, and about whether cloning one would be possible. Here's a bit of a story that ran in the Toronto Globe and Mail on Dec. 20, 2005...

Will woolly mammoths live again?;

Ancient DNA found in frozen mammoth

BYLINE: Anne McIlroy; From Tuesday's Globe and Mail

Scientists have sequenced part of the genome of a woolly mammoth that died 28,000 years ago, a discovery that raises the possibility of bringing the extinct ice age mammals back from the dead.

Hendrik Poinar, a molecular evolutionary geneticist at McMaster University in Hamilton, says ancient DNA obtained from the jawbone of a long-dead Siberian woolly mammoth could be used create a modern version of the animal.

He and his U.S. colleagues won't be able to clone the female that was found frozen in the permafrost because the DNA they obtained was fractured into so many tiny fragments. But they could create a hybrid of the woolly mammoth and its closest living relative, the Indian elephant. Once researchers have made male and female hybrids, they could breed the animals to obtain as pure a woolly mammoth as possible.

"In theory, you could do it," Dr. Poinar says.

It could prove difficult in practice, however. Still, this is the most DNA from an ancient animal that has ever been found and sequenced, he says.

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Windsor, ON: If the mammoth and other big animals went extinct because of a cometary impact (something similar to the Tunguska event, but in a much larger scale), shouldn't we notice some other consequences as well? I mean, the implication is not that the mammoth disappeared in just a moment, but that the impact affected the environment for some time afterwards. Why should that affect only big animals and not smaller ones adapted to the same environmental conditions? Size is important (the bigger you are the more resources you need), but it's not the only factor in the adaptation to the environment. Have you noticed any other consequences coming out of this cometary impact?

Thank you.

Christopher Lee: The scientists who threw up this theory about the comet say there were many other signs of it besides the extintion of the mammoth. Plenty of other large animals --- the giant sloth, the saber-tooth cat, the giant beaver -- that disappeared in the fossil record around this time. Also, they say, there was a big environmental change that resulted, a sudden cooling that lasted about 1,300 years and is known as the Younger Dryas period. The theory is that the dust and other products of the comet explosion triggered the collapse of glacial ice and the flow of ice and fresh water into the North Sea. That in turn interrupted the way heat is transferred from the top to the bottom of the ocean and plunged us back into the Ice Age for another 1,300 years. That's the theory anyway.

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Portland, Ore.: I'm wondering if there is a grand theory of extinction for all species and if the woolly mammoth fits that?

Living in the pacific northwest, what strikes me is that when Mt. St. Helen's blew in 1980, it killed all the large animals nearby, but the smaller ones burrowed underground and lived on.

That kind of fits with the meteor theory of what might of killed of dinosaurs. Did any other animals die off at the time of mammoths?

Christopher Lee: See the earlier post, but yes, plenty of other big animals disappeared around that time, the scientists say. And remember,that many researchers believe that a giant comet or asteroid struck in Mexico's Yucatan peninsula about 65 million years ago, triggering the extinction of the dinosaurs. As for a grand theory of extinction, I'm afraid that there seem to be lots of ways for species to go extinct, some dramatic, some not.

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Chevy Chase, Md.: The assertion that over-hunting by humans may have substantially contributed to the extinction strikes me as questionable just based on the size of these animals, but I'm no expert. In your research, did you learn about significant evidence that paleolithic hunters routinely killed Mammoths? I would think that armed only with spears and perhaps arrows, one would not set out against such large animals unless no other more manageable prey (such as deer or bison, for example) were available. I suppose that large animals can be killed by driving them over cliffs or into pits, but I'm curious what the evidence tells us. Thanks.

Christopher Lee: My understanding is that the evidence tells us that the mammoth was certainly a target for human hunters. Spear tips have been found in fossils of mammoth bones.Think about it: a mammoth is, well, mammoth. If you can bring one of those down, you'd eat for quite a while -- or at least feed a lot of people with a single kill.

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Central Florida: Okay, so the hypothetical atmospheric explosion was supposedly large enough to wipe out megafauna, but why did humans survive? Presumably they are just as liable to incineration or starvation or poisoning as the other animals.

Christopher Lee: Good question, and one that I asked. The response I got was that humans were a more adaptable species of animal than the mammoths were. Mammoths were herbivores. They ate grass, basically, and they needed a lot of it to support their size. The wildfires triggered by the comet explosion would have destroyed the grasslands and left North America a very bleak place for a long time to come. Humans eat just about anything, vegetable or animal. And, I'm just guessing here, humans lived in a variety of environments not just in North America but in Africa, Europe and Asia, too, at that time. A comet wouldn't wipe all of them out. Having said that, the scientists say that in many of the sites they inspected, the spearpoints and other stone tools that were the mark of the Clovis hunting culture end around the time of the comet explosion. So, even if humans did not die out, they presumably were dealt a bad blow.

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Arlington, Mass.: Have other extra-terrestrial impacts been correlated with species extinction?

Christopher Lee: See the post about the dinosaurs and the comet/asteroid strike in the Yucatan. That's probably the most famous example of the theory that an extraterrestrial strike can be an "extinction level event" as they say...

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Annandale, Va.: In correction of the statement in today's article that "...the scientists have not published their findings, ...", Dr. Firestone, Dr. West, and Simon Warwick-Smith authored a book last year which includes a great amount of the data and theory behind their more recent announcements at the Acapulco conference.

The book, entitled "The Cycle of Cosmic Catastrophes", (2006) postulates that at least three different waves of radiation and cosmic material impacted Earth between 44,000 and 13,000 years ago. Many different types of evidence are described, including various particles in a layer just above Clovis artifacts in widely separated locations.

Following just one segment of the theory, I have already made two field trips to "Carolina Bays" within a days drive of Washington to convince myself that these curious geographic features look like impact effects; and that there are tiny magnetic particles scattered in the sand banks at their edges. One cluster of 'Bays' is very visible on Google Earth a few miles inland from Wilmington, N.C., covering most of Bladen County in that state.

Christopher Lee: Actually one of the scientists did mention this to me. My impression, though, is that they have not yet published the research in a peer-reviewed journal, which is a crucial step in scientific circles.

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Pinehurst, N.C.: My understanding is that the Woolly Mammoths were actually eradicated by humans who had migrated to North America during the period when these huge animals roamed the continent. The Mammoths were slow and poorly equipped to avoid the spears of primitive hunters.

Christopher Lee: Yes, this theory, known as the "blitzkrieg" theory, was first put forth by paleoecologist Paul Martin of the University of Arizona in the 1960s. Stone Age big game hunters are thought to have made their way over the land bridge from Siberia to North America, and then killed off the mammoth, the giant sloth, the American camel and other animals, which in turn led the deaths of animals that fed on those creatures, such as the saber-toothed cat. The competing theory is that rising temperatures caused the mass extinctions. One theory along these lines suggests that, as the planet warmed, what had been tundra and grassland turned into forest. While small animals could navigate that kind of landscape to find food, the forest was far less hospitable to big creatures like mammoths who had fed on open grassland.

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Ft Belvoir, Va.: Was there actually an impact?

Christopher Lee: Good question. I'm told that one of the controversial things about the new comet-exploded-and-killed-the-mammoth theory is that there is no evidence of an impact, such as a massive crater. You do get that with the Yucatan strike 65 million years ago. The pro-comet scientists say that there isn't a crater because the comet -- or, more likely, pieces of a comet (the thing broke up as it hit the Earth) -- exploded in the air high over Canada, in between what is now Hudson Bay and the Great Lakes. The telltale signs, they say, are the composition of the sediment layer at the time. All over North America they have found evidence of glasslike carbon, microscopic diamonds and higher than normal levels of the elment iridium, all of which point to a comet explosion, they say. One of the scientists even told me that there is some speculation that the comet explosion created the Great Lakes, but he said it was only speculation and would not be part of whatever they publish.

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Alexandria, Va.: Is there any evidence in the form of human documentation for the exploding comet theory, that is by the North Americans who would have been around at the time?

Christopher Lee: You mean cave drawings of dark skies, a world on fire, that kind of thing? I suspect not -- hard to believe we would not have heard of it already, if there had been -- but if anyone out there has knowledge to the contrary, please write in.

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Derwood, Md.: As a slight change of topic, you mentioned in your opening statement, "I'm happy to chat about the experience of reporting this story". I'd like to address that a bit. How much time do you spend on a story like this? It certainly sounds like you spoke to many experts. How many? Is most of your research book research or interviews? In general, tell us about the actual writing of this story.

Christopher Lee: Hi, thanks for asking. I spent parts of three days writing this story. I interviewed three of the scientists who worked on the comet theory, and two of the British researchers who worked with mammoth DNA. I also read the paper in Current Biology that the British researchers recently published. Since (sadly) I was not at the conference of the American Geophysical Union in Acapulco, Mexico last month, where the comet research was presented, I went back and read news accounts of the meeting to get a sense of what happened. I used that as a starting point for my interviews with the scientists, who explained their findings in greater detail to me. The British researchers, who looked at the DNA, were good sports too. Because of the time difference, I interviewed once scientist at his home in England at what was about 10 o'clock at night for him. (Thanks Dr. Lister!). My interview notes run about 11 pages single spaced, so you can see that a lot of material doesn't make it into the story.

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Takoma Park, Md.: I saw something on TV a few years ago about some miniaturized mammoths surviving on an island off Alaska. Would their extinction also be linked to the comet event?

Christopher Lee: Yes, I came across this too. Radio carbon dating of mammoth tusks, teeth and bones recovered on Wrangel Island in the Arctic suggests that smaller mammoths lived there as recently as 2,000 b.c., so, even if the comet theory is true, some kinds of mammoths lived on after that. The argument is that the comet was the defining event, and that it was all downhill from there.

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Alexandria, Va.: Hi, The idea of somehow "building up" a woolly mammouth via interspecific wide hybridization seems far-fetched. Consider the low fertility and infertility of most interspecific mammalian hybrids in contemporary species. Mules, hennys, and other equine hybrids have been studied for many years and chromosomal differences make them of very low fertility at best.

Christopher Lee: Yeah, it does seem more like the realm of science fiction than science at the moment. Previous DNA research, incidentally, suggests that mammoths are more closely related to Asian elephants than to African elephants. About 95.5 of the mammoth's mitochondrial DNA matches that of the African elephant, while more than 95.8 percent matches that of the Asian elephant.

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Christopher Lee: Folks, we're out of time. Thanks to everyone who looked in or wrote in. Keep your eyes on the skies when they aren't focused on the newspaper (or the Web site, as the case may be). You never know when that next comet is coming!

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