The good folks at Corante are rejiggering the design of their blogs, The Loom included. Some stuff has yet to make the transition as of this writing, but before too long it will all be back in place.

Get to know that little skull. Scientists are going to be talking about it for centuries.

As researchers report in tomorrow's issue of Nature, the skull--and along with other parts of a skeleton--turned up in a cave on the Indonesian island of Flores. Several different dating methods gave the same result: the fossil is about 18,000 years old. (Additional bones from the same cave date back to about 38,000 years.) If all you had was the 18,000 year figure and this picture to go on, you might assume that the skull belonged to a small human child. After all, there is plenty of evidence that Homo sapiens had already been in this part of the world for 25, 000 years. But you'd be wrong.

The skull actually belongs to a previously unknown species of hominid, whose ancestors split off from our own some 2 million years ago. Homo floresiensis, as it's known, stood three feet high as an adult and had a brain less than a third the size of our own.

To understand just how mind-blowing Homo floresiensis is, you have to consider it in the context of hominid evolution. Our closest living relatives (chimpanzees and bonobos) live in Africa, and both genetic and fossil evidence indicate that the common ancestor we share with them lived in Africa as well. The oldest known hominids--those species more closely related to us than chimps or other primates--date back 6 million years. They were short, probably could walk upright, and had brains about the size of a chimpanzee--about 350 cubic centimeters. It was only about 2.6 million years ago that hominids started using stone tools, and only about 2 million years ago that species emerged that stood as tall as we do. Its brain was also bigger--850 cc. The increase in brain size may not have been all that significant, since bigger mammals tend to have bigger brains, smart or not. But shortly after this evolutionary surge, the first hominids turned up outside Africa. Homo erectus moved as far east as China and Indonesia within just a few hundred thousand years. At the very least, their migration suggests an expanding population of meat-eaters who have to seek out much bigger ranges than their ancestors.

The Asian population of Homo erectus had little, if anything, to do with our own origins. The oldest human fossils, dating back 160,000 years ago, were found in Africa, and there's a pretty good chain of evidence showing that Homo sapiens descends from hominids who stayed home on the mother continent while Homo erectus swept across Asia. For instance, African hominids underwent a massive burst of brain expansion around 500,000 years ago to close to our own capacity. Meanwhile, Homo erectus in Asia underwent a slight increase, if any. Humans only expanded successfully out of Africa about 50,000 years ago. They may have interbred with Homo erectus, but most of our genome still points back to a recent African origin.

Paleoanthropologists were first attracted to Flores when 800,000 year old tools were found on the island in 1998. Boats seem to have been essential for getting to Flores, which speaks of a pretty impressive mental capacity for Homo erectus . (On the other hand, lizards and elephants and other land animals got to the island without a boat--perhaps by swimming being swept away on logs during storms.) Researchers poked around on Flores, and last September they turned up something none of them had expected: Homo floresiensis. Homo floresiensis was not an ape--it had the signature traits of a homind, such as a bipedal anatomy and small canine teeth. But it wasn't a pygmy human, either. Pygmy brains are in the normal range of variation for our own species. What's more, the floresiensis brain wasn't just small but had a drastically different shape than ours--a shape more like the brain of Homo erectus. This and other anatomical details have led the researchers to conclude that Homo floresiensis branched off from Homo erectus and evolved into a dwarf form.

Here is case-closed proof that today's solitary existence of Homo sapiens is a fluke in the history of hominids. Even 18,000 years ago, at least one other species walked the Earth with us. Exactly how Homo floresiensis went extinct no one knows, but close to the top of the list would have to be ourselves. Neanderthals survived only a few thousand years after humans turned up in Europe, and Homo erectus seems to have disappeared from Indonesia around 40,000 years ago, just around the time humans came on the scene. Perhaps Homo floresiensis lasted longer on Flores because it was harder for humans to reach.

A dwarf hominid on an island is fascinating for another reason--islands are famous for fostering the evolution of dwarf animals, from deer to mammoths. It's possible that the small territory of islands and the lack of competition and predators favors the small. For the first time, hominids have fallen under the same rule. Islands mammals have also been shown to sometimes evolve much smaller brains, and, incredibly, the hominid brain is subject to the same rule. Homo floresiensis's brain shrank down to the smallest size ever found in a hominid. Did Homo floresiensis lose the mental capacity to use tools along the way? The researchers found stone tools in the same site where they found Homo floresiensis, but it's not clear whether Homo floresiensis made the tools, or humans used them (perhaps to kill Homo floresiensis?).

One of the most interesting questions that comes to mind with the discovery of Homo floresiensis is how far back it goes in the fossil record. Just how long did it take for a lineage of hominids to lose half their height and two-thirds of their brain? It may have taken a million years, or a few hundred thousand, or maybe less. In a commentary in Nature, Marta Lahr and Robert Foley of Cambridge point out that it only took 12-foot high elephants on Malta only 5,000 years to shrink to the size of a dog. I've always been a bit skeptical when people forecast dramatic change for our species. But if evolution can produce Homo floresiensis, who knows what a few thousand years on Mars or another solar system could take our descendants?

Update, 11/1/04: Here's a bundle of papers, interviews, and such on H. floresiensis from Nature. Much of it is free.

I've written a piece for Newsweek about how to program a cell. (The Newsweek International edition comes out this week; the US edition comes out next week.) I find the ongoing research exciting, but sometimes I wonder how much of its promise will become real. Programmable cells, for example, are an illustration of the exciting frontiers that can be explored with stem cells. It may be possible to wire the genetic circuits of a stem cell to make it grow into a particular sort of organ, produce a certain sort of hormone, etc. But it's hard to see how any of that will come to pass if stem cell research withers on the vine. And when I look elsewhere in this week's issue of Newsweek and see how we can't even handle flu vaccines, my hope for medical progress in general starts to dim.

Hope springs eternal, though.

Last month I blogged about my Scientific American review of Dean Hamer's new book, The God Gene. I was not impressed. It's not that I was dismissing the possibility that there might be genetic influences on religious behavior. I just think that the time for writing pop-sci books about the discovery of a "God gene" is after scientists publish their results in a peer-reviewed journal, after the results are independently replicated, and after any hypotheses about the adaptive value of the gene (or genes) have been tested.

Apparently Time doesn't agree. In fact, juding from this week's issue, they think it's the stuff of cover stories. I should point out that the article itself contains some pretty good interviews with people other than Hamer about their own work--studies of spirituality in twins and the like. But Hamer's work gets the lion's share of space, without any mention that his results haven't been published in a journal (let alone that the last results that got Hamer this sort of press--about a "gay gene"--could not be replicated). Time even copied Hamer's title on their cover, despite the fact that in his book, Hamer backpedals furiously from it, saying that the gene he has identified must be one of many genes associated with spirituality. In fact, the Time article has to backpedal, too. It quotes John Burn, medical director of the Institute of Human Genetics at the University of Newcastle in England as saying:

“If someone comes to you and says, ‘We’ve found the gene for X, you can stop them before they get to the end of the sentence.”

You may be able to stop them from getting to the end of the sentence, but you can't stop the presses.

Update, 11/1: The Time story is no longer available for free. I've linked instead to a Time press release.

I have an article in tomorrow's New York Times about the mystery of autumn leaves. Insect warning? Sunscreen? The debate rages. The one thing I was sad to see get cut for space was the statement by one of the scientists that the answer might be "all of the above." This sort of multitasking is the cool--and sometimes maddening--thing about living things. Very important, and very hard to sort out.

Last week I blogged about the strange story of our past encoded in the DNA of lice. We carry two lineages of lice, one of which our Homo sapiens ancestors may have picked up in Asia from another hominid, Homo erectus. I always get a kick imagining human beings, having migrated out of Africa around 50,000 years ago, coming face to face with other species of upright, tool-making, big-brained apes. It's pretty clear that it happened in Europe, which was occupied by both humans and Neanderthals for several thousand years. But encountering Homo erectus would be even weirder. Studies on DNA suggest humans and Neanderthals share an ancestor dating back half a million years or so. But Homo erectus moved into Asia 1.8 million years ago. These were long-lost cousins, to put it mildly. What's more, they almost certainly had nothing along the lines of human language. Their brains were very different too; they kept making the same stone tools they had been making since they had left Africa. I can't help imagining it would have been an awkward encounter, or even a bloody one. Yet it was close enough for us to pick up their lice.

Hot on the heels of the lice study, a new study on human DNA offers some more support to the idea of a very intimate reunion. Until now, most studies of human genes have pointed to Africa as their origin. If you draw a tree of the various versions of a gene, the deepest branches often belong primarily to living Africans. Some genetic markers are shared almost exclusively by Europeans and Asians, which may have evolved as humans moved out of Africa. These patterns suggested that humans sweeping out of Africa did not interbreed with Neanderthals or Homo erectus. Or, if they did, none of the DNA of those other hominids is around today. But in a paper in press in Molecular Biology and Evolution, University of Arizona scientists report the discovery of a gene that flouts the pattern.

Known as RRM2P4, this gene has its roots in Asia. Over half of people sampled from South China had the oldest version of the gene, while only 1 out of 177 Africans who were surveyed had it. And by studying the variation in different versions of the gene, the researchers concluded that the most recent common ancestor of them existed 2 million years ago. The simplest explanation for this pattern is that at least a few humans and Homo erectus came face to face in Asia and had kids.

The authors point out that the gene they looked at isn't big enough to offer a huge amount of statistical confidence. That will have to wait for other genes with Asian roots, if they're out there. But if RRM2P4 is any guide, humans and Homo erectus didn't just trade lice. Our hominid cousins may not have been able to survive as a species with us in the neighborhood, but all was not war between the species.

Here's the most important thing about The Ancestor's Tale that I couldn't fit in my review. I kept noticing how little Richard Dawkins mentioned the other celebrity evolutionary biologist of our time, Stephen Jay Gould. After all, Gould was a prominent character in many of Dawkins's previous books, cast as the brilliant paleontologist misled by leftist ideology.

Gould was famous for his attacks on adaptationism--the notion that the creative powers of natural selection are behind all sorts of fine points of nature, from jealousy to 11-year cicada cycles. Dawkins was an ultra-Darwinian fundamentalist in Gould's opinion. Gould thought that evolutionary biologists should widen their horizons. They should consider that things that look like adaptations might just be by-products of how organisms develop. They should consider how random catastrophes can override all of natural selection's work, wiping out fit and unfit alike. They should consider how selection may work on many levels--not just with selfish genes, but with populations, and even species. (This was why Gould thought punctuated equilibrium was so important.)

Dawkins would have none of this. He downplayed the importance of developmental constraints, of mass extinctions, and species selection. His attitude towards punctuated equilibrium has been, "Yeah, but so what?"

And then, in The Ancestor's Tale, the battle of Dawkins v Gould disappears. One possibility for the disappearance might be that Dawkins is respecting the dead. (Gould died in 2002.) Perhaps, but the silence is still weird. That's because in this book, Dawkins moves into the heart of Gould territory: the murky realm of evolutionary history. Dawkins has always been at his most eloquent and powerful when he ignores history. His arguments about selfish genes and the like are, at their heart, exquisitely organized reasoning. He did sometimes bring in actual details from biology to these arguments, but only as illustrations of his points. In The Ancestor's Tale, Dawkins takes on 4 billion years of evolution, in all its strange exuberance. The evidence--the fossil record, the relationships of living species revealed by DNA, and so on--dwarfs our explanations for it. We know there were giant scorpions in the oceans, and that they disappeared. But we don't know why. We know that birds survived mass extinctions 65 million years ago, but their close relatives--feathered, flightless dinosaurs--did not. But we don't know why. And so on. You'd imagine that this territory might make an adaptationist a bit anxious.

Dawkins handles himself very well as he moves across this terrain. He knows his natural history, his plate tectonics, and all the rest. He frequently throws up his hands about why the history of life took the turns that it did--although he remains confident that the best way to find the answer is to keep adaptationism first and foremost in mind. Gould shows up only in footnotes. Punctuated equilibrium remains an interesting empirical question but not a major principle. Species selection doesn't even show up in the index.

Yet I thought that sometimes Dawkins didn't acknowledge that some of the episodes in evolution he was writing about still raise some important questions about his selfish-gene centered view. I found this to be the case especially when he wrote about the origin of animals. Animals are multicellular organisms, in which trillions of cells come together as an individual, which then reproduces through just a few sex cells. Animals also descend from a single-celled ancestor. Making that transition isn't simple. A bunch of cells won't just come together and agree that a few of them will get to pass their own DNA on to the next generation. That doesn't make evolutionary sense. The only way to decipher this transition is to view evolution taking place at different levels--at the level of the genes, of the cell, and of the individual. Changes at one level may work against changes at the others, or they may all end up working together. I got interested myself in this subject a couple years ago while writing an essay for Natural History, focusing on the work of Richard Michod of the University of Arizona. It seems to me that the origin of animals is a case where Gould's multi-level selection may work well. Now, Dawkins might disagree, and yet he didn't even mention this challenge to his own views, let alone tear it apart as you'd expect from his previous books. In a 630 page long book, I find this omission puzzling.

It's always possible that Dawkins might eventually accept that in this case multi-level selection is important. He'd probably go on arguing that in most cases a gene-centered approach to life works best. I found it very interesting that he ends the book with a discussion of religion, saying that he suspects that many who call themselves religious would agree with Dawkins (an outspoken atheist) on many of the things he has to say about nature. He describes how "a distinguished elder statesman of my subject" was arguing for a long time with a colleague. The statesman said jokingly, "You know, we really do agree. It's just that you say it wrong."

I imagine Dawkins talking to Gould there.

The New York Times is running my review of Richard Dawkins's new book The Ancestor's Tale this weekend.

I'm particularly grateful at times like these to have a blog, where I can add extra information and the occasional correction.

Towards the start of the review I mention a remarkable tree of 3,000 species. You can download a pdf here. It's files like these that the zoom function were made for.

Towards the end of the review, I say that jellyfish and humans share a common ancestor that lived perhaps a billion years ago. There's plenty of debate about early animal evolution, but a billion years is probably too old--700 million or 800 million would have been better. Maybe I was thinking about fungi instead of jellyfish.

When I have a little more time today, I'll blog about some of the things that I think Dawkins should have included in his book but didn't.

Yesterday I blogged about how the National Park Service is selling a young-Earth creationist book about the Grand Canyon in its stores. Today the Washington Post wrote an article on the subject. It contains a response from the National Park Service, which I find pretty unbelievable. They claim that they are in fact reviewing the matter. The review was supposed to be done in February, but it's been delayed while lawyers at the Interior and Justice Departments "tackle the issue." No deadline is set for the decision, and the book will continue to be sold until one is made.

Tackle the issue? Do these folks really need an extra eight months (and counting) to recognize that the Grand Canyon is millions of years old, and was not formed in Noah's Flood?

The book has been moved from the science section to the inspirational section. But from what I know about it, it's not claiming to offer inspiration but facts. The intellectual cowardice continues.

Continue reading "Further Adventures in Geological Cowardice"

David Appell points to some depressing news about how our government deals with science.

In August 2003, the Grand Canyon National Park Superintendent tried to block the sale of a book in National Park Service stores. The book claims that the Grand Canyon formed in Noah's Flood. No vague ambiguity of the sort you hear from Intelligent Design folks--just hard-core young Earth creationism, claiming that the planet is only a few thousand years old. The folks at National Park Service headquarters stopped the administrator from pulling the book. Geologists cried foul, and NPS promised to review the situation. Meanwhile, the book remained for sale at NPS stores.

And then months passed with nothing. Today a public employees activist group that first publicized this sorry situation announced that it has documents showing that the administration has decided to let the book stay. In fact, there wasn't even any review.

I haven't seen any news pieces yet on this shamefulness, nor have I seen any statement from the National Park Service. From the information we have at hand at the moment, there's only one good conclusion to draw: your government is indifferent to even the most basic facts of science. If it doesn't care about something as well-established as the age of the Earth, you have to wonder what other science it is willing to ignore.

A lot of readers have commented on my recent post about a study that suggests we all share a common ancestor who lived 2,300 years ago. Some people doubted that isolated groups could share such a recent ancestry.

One of the study's authors, Steve Olson (also the author of the book Mapping Human History) sent me the following email yesterday:

"Ensuring a recent common ancestor doesn't take long-range migrations (although contact between the Polynesians and South Americans certainly speeds things up).  All it really requires is that a person from one village occasionally mates with a person from an adjoining village; after that the power of exponential growth, and the dynamics of small worlds networks, take over.  As for counterexamples, I've been looking for five years for examples of populations that were completely isolated, and I've decided that they're rare to the point of nonexistence.  The Tasmanians are a possibility, but it's only 60 miles from Tasmania to Australia -- that no one made that trip in 9,000 years seems counterintuitive to me.  And of course it only takes one person to link two genealogical networks, even though the amount of gene flow represented by that one person may be negligible (though I also think that gene flow in the past has been much more extensive and much more continuous than most people imagine)."

In March, I wrote a post on some tantalizing new findings about the secrets of human evolution lurking in our genome. In brief, researchers at the University of Pennsylvania studied a gene called MYH16 that helps build jaw muscles in primates. In our own lineage, the gene has mutated and is no longer active in jaw muscles. Perhaps not coincidentally, we have much smaller, weaker jaws than other apes. The researchers estimated that the gene shut down around 2.4 million years ago--right around the time when hominid brains began to expand. They suggested that shrinking jaw muscles opened up room in the hominid head for a larger brain.

It's a cool hypothesis, but it may not hold up. Scientists at Arizona State University have followed up on the initial study by anlayzing much larger pieces of MYH16, both in humans and in other species. All told, they studied 25 times more DNA from the gene. In a paper in press at Molecular Biology and Evolution, they report finding a significantly different date for when the gene mutated. Instead of 2.4 million years ago, they get a much older date: 5.3 million years ago.

If that's true, then you can forget any significant link between the evolution of MYH16 and brain evolution. If the Arizona State team is right, the two events are separated by three million years. What's more, the jaws of hominids also remained relatively large after the mutation of MYH16.

The Arizona State researchers do point out an intriguing clue that may eventually lead to a solution to this paradox. The mutation that the Penn team originally argued that the MYH16 gene became useless when a section of DNA in the middle of its sequence was accidentally deleted. Often, when this sort of deletion takes place, DNA-copying enzymes come to a screeching halt at the site of the mutation. With the gene only partly copied, it cannot be turned into a protein. But the Arizona State researchers found signs that the gene did not shut down entirely 5.3 million years ago. The DNA "downstream" from the mutation--in other words, beyond the point where the enzymes stopped copying the gene--has picked up mutations in a pattern that shows no sign of natural selection at work. That's what you'd expect from DNA that doesn't make a gene, since any change will have no effect for good or bad on its owner. But the upstream DNA--the part of the gene that could still be copied--told a different story. It showed signs of having undergone selection. So perhaps the mutation that occurred 5.3 million years ago didn't actually kill the gene, but just amputated it. What the surviving portion of MYH16 did (or still does) remains unknown.

I would wager that this new paper will unfortunately not attract much press. When scientists first come up with an attention-grabbing hypothesis, they're more likely to get a paper accepted to a high-profile journal, and more likely still to get written up by science writers like me. But follow-up work often ends up in the shadows.

That's a shame, because science is actually not made up of single studies that suddenly overturn everything that came before. It's more of a dialectic, as different groups of scientists search for new evidence in order to put hypotheses to new tests. Some hypotheses--such as the idea that chimpanzees are our closest living relatives--have become stronger over time. Others fall away. It would help if more people understood this process. Unfortunately, it seems that a lot of people think science is like building an elaborate sculpture out of glass. If someone discovers that a piece of research is wrong, then it seems as if the whole sculpture cracks and falls to the ground. Creationists are particularly fond of this tactic. They seize on research about evolution that goes against earlier research, and claim that the entire theory of evolution is a fraud. They conveniently ignore all points on which scientists agree. So, for example, the researchers who have published the new findings on MYH16 do not conclude that humans were intelligently designed, MYH16 and all. Instead, they argue that the gene mutated earlier than once believed, and that the full history of this gene remains to be revealed. Science is more like a sculpture made of clay than glass, continually being molded and reshaped to better reflect reality.

Correction, 10/16/04: Changed "ancestors" to "relatives."

Contempt is never wise in biology. The creature that you look down on as lowly, degenerate, or disgusting may actually turn out to be sophisticated, successful, and--in some cases--waiting to tell you a lot about yourself. That's certainly the case for lice.

The human body louse, Pediculus humanus, has two ways of making a living--either dwelling on the scalp, feeding on blood, or snuggling into our clothes and come out once or twice a day to graze on our bodies. For lice, we humans are the world. They cannot live for more than a few hours away from our bodies.Only by crawling from one host to the next does their species escape extinction.

A group of louse specialists recently decided to find out where human lice came from. Have they been riding on our bodies since before we were human? A comparison of the lice that live on different primates shows that they certainly can be very loyal. If you draw an evolutionary tree of primates, and then draw a tree of their lice, they are almost identical. On the other hand, some lice can live on more than one species. And a side-by-side comparison of trees reveals that in some cases they don't form a perfect mirror. In other words, sometimes lice can make an evolutionary leap.

As the researchers report today in Public Library of Biology, they compared human lice to the lice of primates, looking at both their DNA and their anatomy. As earlier research had shown, they found a major split among lice species that live on apes and on monkeys and other primates. That reflects an ancient split in the primates themselves: our ape ancestors diverged from other primates 20-25 million years ago. The variation in louse DNA turns out to act like a sort of molecular clock, showing when they split into different lineages. The molecular clock puts the split between lice that live on humans and chimps at 5.6 million years ago--exquisitely close to the age that's been estimated for humans from studies on both DNA and fossils.

The research suggested that we've carried our lice for millions of years, since before the time of our common ancestor with chimpanzees. But after we parted company with the chimps, the lice have a remarkable story to tell. Human lice split into two lineages. One lineages is found around the world. The second is found only in North America. The worldwide branch all share a common ancestor that lived 540,000 years ago. The North American branch shares a common ancestor that lived 150,000 years ago. And finally, the two branches share a far older common ancestor, which lived a 1,180,000 years ago.

So how did these two strains of the same species become separated and then wind up back on our bodies? The researchers argue that human evolution holds the key. Paleoanthropologists and geneticists still debate over the origins of modern humans, but the rough outlines are becoming clear. The first hominids to emerge that were tall, big-brained bipeds--that weren't just upright apes, in other words--lived about 2 million years ago. They very quickly began to spread out of their birthplace in Africa to other parts of the world. They were in the Caucusus mountains 1.8 million years ago and China 1.66 million years ago. These hominids are generally called Homo erectus, although they may well have consisted of several species, rather than one. And the ranks of Asian Homo erectus may have been boosted by fresh migrations of African hominids when ecological conditions favored another journey out of Africa. But it does appear that Asian populations became pretty isolated from African hominids. The fossils of Homo erectus from a few hundred thousand years ago look pretty distinct from both African hominids and Neanderthals, with very thick skull walls and other peculiar anatomical details. Thirty years ago, most paleoanthropologists would have told you that these Asian hominids probably were the ancestors of living Asians. But that's not what the evidence gathered since then suggests. Instead, it now looks pretty clear that Homo erectus was a very distinct species than Homo sapiens, and became extinct perhaps as recently as 30,000 years ago.

Our own roots can be found in Africa. The oldest clear cut examples of Homo sapiens fossils, found in Ethiopia, date back 160,000 years. By about 100,000 years ago, our species was beginning to diverge into different populations, and these differences can still be found in the DNA of various African groups, such as the Khoisan of Southern Africa (sometimes called bushmen). By 50,000 years ago, humans were moving out of Africa. In Europe, they moved into territory occupied by Neanderthals and their ancestors for some 300,000 years. Neanderthals disappeared by 28,000 years ago. They seem to have been driven into mountainous refuges by the booming population of humans. The story in Asia has always been a bit fuzzier. Humans appear to have gotten to Australia by at least 40,000 years ago, and perhaps much earlier. By 15,000 years ago, some Asian populations of Homo sapiens made their way into the New World through Alaska. Exactly where Homo erectus was on their arrival in Asia, and how long they survived, has never been clear. It hasn't even been clear whether the two species came into contact or not.

You may be able to guess how the louse scientists interpret the data from their parasitic charges. When Homo erectus moved into Asia and became isolated from our own ancestors, their lice became isolated as well. When our own ancestors burst out of Africa around 50,000 years ago, they carried the African lice with them. The most sensational part of the story comes when humans arrive in Asia. The researchers argue that a population of humans encountered Homo erectus and picked up their lice. Their descendants then passed into North America, where they--and their lice--live today. One of the many intriguing implications of this research is that the contact may have occurred in one limited regions--the same region where Native Americans originated in Asia.

This is not the first case where our parasites have preserved our own hidden history. Our tapeworms, for example, can tell us about how our ancestors began eating meat. Malaria reveals how agriculture brought new diseases to humans over the past few thousand years. Helicobacter pylori, the bacteria that trigger stomach ulcers, maps the spread of modern humans. (I go into more detail on some of these examples in my book Parasite Rex.) And the lice probably have more to tell us.

For example, the scientists can't say for sure how humans most likely picked up Homo erectus's lice. The contact definitely had to be intimate. But did it occur when humans drove Homo erectus away from their kills? Or did these two species make love, rather than war? Although the genetic evidence indicates that Homo erectus could not have contributed a significant number of genes to our species, it's possible that they contributed a few. The answer to this question may help show how Homo erectus became extinct, leaving us as the sole hominids left on Earth.

One way to test that possibility will be to look at the other species of lice that live on humans--crabs, or Pthirus pubis. If our ancestors got body lice from Homo erectus during sex, they probably got crabs as well. Somehow, though, I'm guessing that putting together a global collection of crabs may take a little bit longer than the body lice. But it will definitely be worth the wait.

UPDATE: 10/4 9:50 PM: A question occurs to me: why didn't we pick up Neanderthal lice?

UPDATE: 10/5 6:20 PM: The link to the paper is fixed (and the paper is free--bless PLOS!)

Congratulations to Linda Buck and Richard Axel for winning the Nobel Prize for Medicine today. They won for their pioneering work on the 600 or so receptors that we use to smell. As is so often the case these days, the research that wins people the Nobel for Medicine also reveals a lot about our evolution. This February, for example, Buck published a paper in the Proceedings of the National Academy of Sciences, in which she and her colleagues charted the evolutionary history of human olfactory receptors.

As Buck explains, it appears that many olfactory receptor genes mutated beyond repair in our lineage as we came to rely more on sight than smell. Only about half of the olfactory receptor genes in the human genome actually produce working proteins. (You can find working versions of these genes in other animals). Other researchers, however, have found that some human olfactory genes have undergone strong natural selection, which suggests that it's still a good idea to be able to sniff out a piece of rotten meat. (If you want more details on this line of research, you can read an essay I wrote a couple years ago for Natural History.)

And yet, somehow creationsists and their ilk keep a straight face as they continue to tell us that evolution is a dying myth. In this month's Wired, for example, techno-know-nothing George Gilder declares "Darwinian materialism is an embarrassing cartoon of modern science." When Gilder gets to run the Nobel Prize committee, I guess he can take back Buck's medal.