Blogs / The Loom

If you don’t already subscribe to Science and the City, a podcast from the New York Academy of Science, do so. They pick a great mix of intriguing topics, from the origin of the solar system to the physics of kite-flying. I was delighted that they gave me a call for their latest podcast to talk about The Tangled Bank. Our conversation ranged from the evolution of eyes to the power of good science illustrations. Listen here.

Charles Darwin was interested not just in how new things evolve, but also in how old things disappear. Often, they don’t disappear completely without a trace. We don’t have a visible tail like our primate ancestors did, but we still have a series of little bones tucked away at the bottom of the spine. While it may not function like a full-blown tail, it still anchors muscles around the pelvis. Blind cavefish may not have eyes of the sort found on their cousins in the outside world, but they still start to develop eyes as larva, before the cells start to die away.

Sometimes, though, the only place to look for vestiges of a lost trait is in a genome.

In the journal PLOS Genetics, Mark Springer of the University of California and his colleagues have published an intriguing study of how teeth–and the genes for teeth–have faded away over the past 50 million years. In particular, they looked at enamel, the tough covering that caps the teeth of humans and other vertebrates.

Enamel has three advantages for this kind of study: one is that it fossilizes well. For a lot of species, enamel is often the only thing left behind. Another advantage of enamel is that scientists also have a good understanding of the genes that build it–genes that are similar across a wide range of species. And the third advantage of enamel is that certain lineages of mammals have lost it. Baleen whales, anteaters, and pangolins have all lost their teeth entirely. (Baleen whales grow tooth buds, like cave fish grow eyes, but the buds die back without ever forming enamel.) Sloths, armadillos, pygmy sperm whales, and aardvarks still have teeth, but have no enamel left. This pattern suggests that enamel has been lost independently in several lineages of mammals.

In each lineage, these mammals have lost enamel as they’ve shifted away from depending on hard teeth. As I wrote about here, baleen whales descend from ancestors with formidable teeth for catching prey. But then their ancestors evolved a new way to eat, growing baleen–frond-like sheets of tissue that can filter out krill and other small animals from sea water. As anteaters came to only eat insects, the teeth of their ancestors became not just pointless but a hindrance. Their mouth became finely adapted for shooting a long tongue forward into ant nests. Big teeth would just get in the way.

So where did the enamel go? The scientists decided to test the possibility that the genes for enamel were still in the genomes of toothless mammals, but they had been shut down. In each species’s genome, scientists find a number of so-called pseudogenes, which can no longer encode a protein because of a crippling mutation. A mutation may, for example, insert a “stop” command, so that cells can no longer read the full sequence of a gene and make a full protein. Other mutations can shift a big chunk of DNA over a couple positions, garbling the code. Imagine shifting all the spaces in a sentence to the left. Y ouwou ldg etsomethi ngli kethis.

Despite these devastating mutations, pseudogenes often manage to retain a strong resemblance to their working counterparts. We, for example, have hundreds of pseudogenes that show a striking resemblance to hundreds of other genes that encode a variety of receptors in our noses. So Springer and his colleagues sequenced an enamel-building gene called ENAM in 49 mammal species, including toothless or enamel-less ones to see what happened to the gene along the way.

Their results were pretty much what they expected, but they’re still pretty amazing. There were no frameshift mutations in ENAM among the mammals with teeth. But 17 out of 20 species without teeth or enamel had at least one. In all 20 enamel-free species, a stop command (known as a stop codon) was present. These genes are shot.

The scientists then probed the evolution of the ENAM genes by taking advantage of the fact that only some letters in a gene encode a protein and others are ignored. Mutations that change the structure of a protein may have serious effects on an animal. They may be good effects or really bad ones–in either case, they may change the overall reproductive success of individuals who carry the mutation. On the other hand, silent mutations may have no effect (or at least just a small one).

It turns out that in mammals with teeth, the ENAM gene has experienced something call purifying selection. In other words, very few protein-changing mutations have endured for millions of years because tinkering with the recipe for enamel is a really bad thing to do if you need hard teeth to survive. In mammals without enamel, on the other hand, the ENAM gene evolved in a different way. It experienced what’s known as neutral evolution: the silent mutations and the protein-changing ones have occurred at about the same rate. It just doesn’t matter to the mammals anymore, because the genes are, as I mentioned before, shot.

These genomic vestiges don’t just provide evidence of how teeth were lost. They also provide some clues to when they were lost. By comparing closely related species that don’t have enamel, the scientists could tally up the mutations that had arisen since their last common ancestor. And since neutral mutations tend to pile up at a fairly steady rate, the scientists were able to estimate how long ago the ENAM gene turned from an essential gene to a useless one. In some cases, the scientists predict, paleontologists will find toothless members of these lineages millions of years older than the oldest known fossils without teeth–such as with pangolins, as this figure illustrates.. It is a remarkable convergence, of traces of history recorded in molecules tucked away in anteater cells, and skulls that have managed to turn to stone. But from them, a single picture emerges.

The stork UPS man pitched a box through the front door this morning. Inside was an advance copy of my new book, The Tangled Bank: An Introduction to Evolution. The paternal photographer in me took over, and now I have to show off my snaps. Above is a picture that I like for two reasons. One is the way it shows off Carl Buell’s lovely (and crowd-critiqued) cover. The other is the way it illustrates the book’s far-less-than-a-doorstop mass, which is all too typical for textbooks these days. In fact, the book’s smaller than Tino, our far-less-than-a-doorstop cat.

I also took some pictures of the inside, because I’m always astonished by how different pictures and text look when they’re actually on a physical book page, rather than on a monitor or spat out from a printer. (Fortunately, in this case, they look better.)

Here’s a typical chapter opener–living microbes growing in mats (known as stromatolites) above 3.5 billion year old fossils of stromatolites (some of the oldest evidence of life on Earth). To the right is paleontologist Abigail Allwood, who studies these fossils.

Conveying the vast time scales of life’s history is a perennial challenge. We chose to run a timeline across the front and back endpapers (the back one, covering the last 600 million years is in this picture).

Another challenge in a book like this is to get readers to start thinking about evolution in trees, rather than as linear marches of progress. Kevin Padian, a UC Berkeley paleontologist (and Tangled Bank advisor), has called for new illustrations he calls “evograms.” These are pictures that combining the branches of the tree of life with details showing homologies and fossil evidence. (Here’s an open-access paper he wrote about evograms last year.) I have a number of evograms in my book, like this one for birds. I think The Tangled Bank is the first textbook to use evograms, and now that they’re in print, I am glad I followed Kevin’s advice.

Of course, while the tree of life is a powerful metaphor for evolution, it does not work in some cases. I particularly liked the way the biologists Ford Doolittle and Tal Dagan have visualized the complex, web-like patterns of evolution brought about by horizontal gene transfer. So I included them in the book, too.

And, of course, the book includes as many paintings as we could squeeze out of Carl Buell. Here’s one showing the convergent evolution of saber toothed marsupials and placentals.

The book’s not perfect, of course; I see things I should have done better, and even a couple errors to be fixed at the soonest opportunity. I’ll set up an errata page when the book comes out in October, and I’ll welcome notes from readers. But, for now, I’m just reveling in the real-ness.

(To see what E.O. Wilson and other biologists have to say about The Tangled Bank, check out this post.)

Chimpanzees get AIDS.

This is an important discovery, but what intrigues me most about it is how the discovery was made. It is a story of two kinds of science, both of which are essential to getting a deeper understanding of life, but which today are staggeringly out of balance.

In the 1960s, Jane Goodall carried out some of the first long-term studies on chimpanzees in the wild. Goodall made important observations, noting that chimpanzees can be surprisingly cooperative but also quite violent, with troops engaging in war-like conflicts.

Goodall’s research was part of a long tradition of going to where the animals are, and tracking them for years on end. Goodall didn’t take giant crates of lab equipment with her to Tanzania; instead, she brought patience and careful observation.

Of course, doing this sort of science poses some serious challenges. Field biologists often end up studying relatively few individual animals, because they’re so hard to find. Small sample sizes always make sweeping generalizations risky. Animals in the wild are also embedded in a marvelously complex environment. They are influenced by a vast number of variables–the weather, the food supply, the latest disease outbreak, the latest kerfuffle between the top male and his younger rivals. The state of an animal at any moment may be influenced by many of these variables, making it even harder to uncover important underlying rules of its natural history. And since this kind of science takes so long, it can seem meager if you only learn about it through the papers that the scientists publish.

The contrast between Goodall’s kind of science and, what goes on in, say, a virology lab is enormous. Instead of just watching viruses, scientists can run experiments to test hypotheses–experiments that are controlled with exquisite precision. Scientists can genetically alter viruses to discover how each bit of its genetic material helps (or doesn’t help) it infect its host. They can carefully select the hosts to infect, comparing two sets of hosts for instance that might differ only in one particular cell receptor. They can trace the virus’s journey through the cell and out again; they can sequence viral genes as easily as you might crack open a fortune cookie. And they can churn out many papers a year on what they discover.

The divide between these different kinds of biology has existed for decades, as I wrote in this essay for PLOS Computational Biology. That divide has led to some unfortunate biases. Natural history is sometimes treated like glorified butterfly-collecting. Meanwhile, lab-based molecular biology is sometimes seen as sterile and pointlessly reductionist. But it would be a mistake for one side to think it could live without the other. Understanding the origin of AIDS is a case in point.

In 2007, an estimated 33 million people worldwide had HIV infections, and an estimated 3.1 million people were dying of AIDS-related causes every year. Yet, as diseases go, HIV is a latecomer. Scientists only became aware of it in the early 1980s, when it was still relatively rare, after which it swiftly became a global epidemic. Scientists have tried to search through medical records and blood samples for earlier cases of HIV infection that might have been overlooked. The earliest sample of HIV comes from a blood sample taken from a patient in Kinshasa, the capital of the Democratic Republic of Congo, in 1959.

The mysterious appearance of HIV led to many speculations about where it came from–including accusations that vaccination campaigns introduced it into people with vaccines contaminated with a monkey virus. But when scientists reconstruct the evolutionary tree of the virus and its relatives, they can reject those claims.

As soon as scientists discovered HIV, it was clear that it belonged to a group known as the lentiviruses. Lentiviruses are small particles with spiky knobs on their surface, and they encode their genes in RNA. They infect mammals, such as cats, horses, and primates, typically invading certain types of white blood cells. Genetic studies revealed that HIV is most closely related to strains of lentivirus that infect monkeys and apes–known as simian immunodeficiency virus, or SIV for short. HIV is not actually a single lineage. It is several different strains with different origins.

There are two main forms of HIV, HIV-1 and HIV-2. HIV-2, which is relatively mild, evolved from SIV that live in a monkey called the sooty mangabey. The story of HIV-1, which  causes the vast majority of AIDS cases, is more complicated, as this diagram shows. (It comes from my upcoming book, The Tangled Bank: An Introduction to Evolution.) This tree reveals that it is actually several strains, all of which jumped from chimpanzees.

Scientists first discovered SIV in chimpanzees by looking at captive animals. But in order to get a sense of the true diversity of the virus, they had to leave the relative comforts of laboratories and head out to the places where chimpanzees live. Wild chimpanzees don’t take very well to a blood draw, so scientists developed methods for extracting virus DNA from the feces chimpanzees leave behind. But in order to find those chimp feces, you have to find the chimps (and the trees in which they spend the night).

These studies showed that two subspecies of chimpanzees carry SIV, but HIV-1 has only evolved from one, P. troglodytes trogloydytes, found in west Africa around Kinshasa (marked Ptt on this tree). Goodall’s central African chimpanzees, Pan troglodytes schweinfurthii, have SIV of their own (Pts).

These studies indicate that SIV evolved into HIV as hunters killed apes and monkeys to sell in a growing “bush-meat” industry. Viruses in the blood of the primates could have entered cuts in the skin of the hunters, where a few of them mutated and evolved adaptations to their new host.

Knowing the structure of the HIV tree allows scientists to pinpoint those adaptations. It turns out, for example, that as all three strains of HIV-1 evolved from chimp virus ancestors, they all acquired the same new amino acid in the same position in the same protein. No strain of SIV in chimpanzees produces that amino acid. This mutation altered a gene encoding the shell of the virus, and experiments suggest that it was crucial to the success of the new HIV strains in humans. It’s possible that the mutation allowed the virus to do a better job of manipulating its new hosts into building new copies of itself.

Of course, AIDS is more than just a virus. Once a person is infected with HIV, it may take years for the virus to wipe out his or her immune system, allowing a menagerie of parasites to move in. When scientists studied captive chimpanzees infected with SIV, they didn’t see anything that looked like AIDS. This was intriguing to say the least. Perhaps the chimpanzees and the viruses had coevolved to a peaceful coexistence. When HIV-1 jumped to humans, its evolution took a nasty turn.

But what about chimpanzees out in the real world? Do they get AIDS? That’s a very short question that has taken a very long time to answer. A team of scientists set up shop at Jane Goodall’s study site in Gombe National Park, and took advantage of her decades of field work to track 94 individual chimpanzees for nine years. They searched chimpanzee feces for SIV, and then kept track of the chimpanzees themselves, observing their health, their offspring, and their lifespan. When the chimpanzees died, the scientists autopsied them to see what effect, if any, SIV had on them.

The results, published today in Nature, are stark. Out of the 94 chimpanzees, 17 had SIV. The SIV-infected chimpanzees had a mortality rate 10 to 16 times higher than the uninfected chimpanzees. Fewer infected female chimpanzees gave birth than uninfected ones, and none of their babies survived to a year. Pathologists found that dead infected chimpanzees looked like they had AIDS, with a lower level of immune cells called CD4+ T cells and damaged lymph tissue.

This discovery raises all sorts of questions. The Gombe chimps get sick, but not as sick as humans do from HIV-1. Why? There’s no evidence that SIV jumped into humans from P. t. schweinfurthii. Instead, it jumped three or more times from P. t. troglodytes. As far as anyone knows, those chimpanzees don’t get AIDS. But, then again, nobody has yet published a study like the one that has just come out on the Gombe chimps. What will that study reveal, if anyone ever carries it out? Is P. t. trogolodytes the source of a recent infection of both humans and the Gombe chimps?

And what’s particularly interesting, to me at least, is the fact that scientists had not noticed chimp AIDS before. Robin Weiss, an HIV researcher at University College London, and Jonathan Heeney of the University of Cambridge, published a commentary in Nature in which they suggest that the artificial conditions in which captive chimpanzees live protect them from AIDS. Out in the real world, where chimpanzees face an onslaught of pathogens, infections may activate the immune system in a way that brings on the virus’s attack and, ultimately, AIDS.

In other words, only the slow-cooked science pioneered by Jane Goodall allowed scientists to discover one of the most fundamental facts about a virus that has become one of the most devastating scourges humanity has faced in modern history. Slow-cooked science may provide more clues in the future–but only if its value is recognized, and only if chimpanzees can survive SIV and all the other threats to their survival these days.

[Goodall image: Jane Goodall's Chimpanzees]

In response to my post on the endorsements for The Tangled Bank: An Introduction to Evolution, a lot of commenters had questions and reactions. I’ve responded in the comment thread here.

My publisher has been sending out copies of The Tangled Bank: An Introduction to Evolution to some leading biologists for possible endorsements when it comes out in October. Here’s what we’re hearing back so far…

“The Tangled Bank is the best written and best illustrated introduction to evolution of the Darwin centennial decade, and also the most conversant with ongoing research. It is excellent for students, the general public, and even other biologists.” –Edward O. Wilson, Harvard University, author of Consilience

“Carl Zimmer’s excursion through the evolutionary epic is without equal.  His gift for the scientific narrative is on full display through The Tangled Bank, and he leads his readers onward with an energy and delight that never disappoints. This marvelous text is an extraordinary introduction to the depth and richness of evolutionary science.” –Kenneth Miller, Brown University, author of Only a Theory: Evolution and the Battle for America’s Soul and co-author of Miller & Levine’s Biology

“Zimmer has produced a wonderfully thorough introduction to evolutionary biology. With his prose and color diagrams by leading artists produced specially for this volume, The Tangled Bank will be a powerful tool to introduce students to the explanatory power of evolution and the way that it integrates different fields of knowledge. I have no doubt that this important volume will find its way into diverse courses in the curriculum.” –Neil Shubin, University of Chicago, author of Your Inner Fish

“One rarely says of a textbook, ‘I couldn’t put it down,’ but that was how I felt reading Carl Zimmer’s Tangled Bank. Zimmer has applied his award-winning communication skills to producing a readable yet up-to-date and thorough treatment of evolutionary biology. Were I teaching evolution, this is the book I would use.” — Eugenie Scott, Executive Director of the National Center For Science Education and winner of the 2009 Stephen Jay Gould Prize

“Carl Zimmer’s The Tangled Bank is a joy to read. He draws readers into the excitement of the rapidly expanding science of evolutionary biology, as he explains why life on earth is so diverse and how the web of life evolved to be so entangled.  He explains, through elegant prose and beautiful illustrations, the remarkable progress that has been made in recent years in understanding the evolutionary process.” –John Thompson, University of California, Santa Cruz, author of The Geographic Mosaic of Coevolution

“This engagingly written and well-organized book is a wonderful introduction to evolutionary biology.  It beautifully synthesizes the conceptual basis of evolutionary theory with the empirical evidence that evolution has occurred.  The book is remarkably up-to-date, seamlessly moving from discussion of fossils to genomes, and nicely illustrates that evolutionary biology is a vigorous field that increasingly takes an experimental approach.” — Jonathan Losos, Harvard University

[Update 7/6: Two new ones below]

“In clear, accessible prose, Carl Zimmer explains how 21st century science confirms the 19th century’s most radical idea. If you want to understand life’s remarkable past and uncertain future, read The Tangled Bank.” –Andrew Knoll, Harvard University, author of Life on a Young Planet: The First Three Billion Years of Evolution on Earth

“Zimmer weaves cutting-edge findings and essential concepts around the personalities and adventures of the biologists themselves. The result is superb: an up-to-date, articulate, and gorgeously illustrated introduction to modern evolutionary biology. We sorely needed a text aimed at the nonmajor undergraduate, and Zimmer was exactly the right person to write it.” –Douglas J. Emlen, Professor of Biology, University of Montana

To all of these biologists, many thanks from this old English major.

(And, by the way, that is the final cover. Thanks to the 1018 people who cast votes on their favorite mock-ups, as well as to the many who didn’t like any of them and asked, “Where’s the tangled bank?”  You spoke, I listened. In the end, I decided to go with Tiktaalik, but give it some extra company–both animal and vegetable–based on fossils that also date back to this sort of ecosystem 370 million years ago. Thanks to Carl Buell, as ever, for making that idea into a cover.)

Fireflies are the topic of my story on the cover of the New York Times science section tomorrow. It’s the result of a visit I paid last Friday evening to a meadow in Massachusetts, where I listened to Sara Lewis of Tufts University explain the sultry, complex tale of sex, deception, and death that was playing out in front of me.

I first got to know Lewis’s work last summer, when I decided I wanted to include fireflies in my next book, The Tangled Bank: An Introduction to Evolution. Lewis co-authored a fascinating review of firefly biology last year (free pdf from Lewis’s web site). I particularly liked this chart, which shows how different species have evolved different flash signals.

The male, flying around, releases a certain pattern of flashes–a single one second pulse followed by a five secondin the case of Photinus pyralis, for one example. And if a female P. pyralis, sitting on a blade of grass, likes what she sees, she responds three seconds later. Not one. Not six. Three. If she responds at the right interval, he knows he’s found a female of his own species and zeroes in, sending more flashes. She may also be signalling other males at the same time; which male she chooses may come down to subtle features of the flash pattern–for example, a rapid series of pulses as opposed to a slow one.

You can, as I discovered, speak their language with a penlight. You can even play the male or the female, depending on your mood.

There’s lots of strange business going on out among the fireflies. I didn’t have room in the article to describe some of Lewis’s new areas of research. Because female fireflies mate with several males, they can end up with sperm from several males inside them at once. Studies on other animals have suggested that females can choose which male’s sperm they’ll use to fertilize their eggs. Males can also inject chemicals with their sperm that increase their odds of fertilization. It’s clear that in many species, female preferences and male competition can continue after mating ends.

No one knows how this struggle plays out in fireflies. Adam South, one of Dr. Lewis’s graduate students, is investigating this side of the evolutionary equation. He is mating female fireflies with two males apiece and then collecting the eggs they lay. Using DNA tests, he’s determining the paternity of the eggs. Perhaps the males with more attractive flashes have more offspring.

What scientists like Lewis know about fireflies is remarkable, but it’s dwarfed by what they don’t know. Are fireflies on the decline, for example? Unfortunately, there’s no good long-term data. But that’s now an opportunity for some citizen-science you can get involved in. Lewis and some former students have helped organize Firefly Watch, based at the Boston Museum of Science. You can make your backyard part of biology’s new frontier.

Last month, I asked you how to handle the ever-growing pile of science books I receive (before I donate most of them to the library, of course). A plurality of you voted in favor of frequent thumbnail descriptions, rather than alternatives like the less frequent all-out review. That’s a relief, because that was my own preference. So let me pull off the top book from the pile,  Life Ascending: The Ten Great Inventions of Evolution by Nick Lane.

The reason it’s on the top is that it happened to be very useful to me right now with an article I’m working on (more on that next month). Lane has selected a handful of key features of the natural world, from DNA to sex to warm-bloodedness to consciousness, and has written a chapter about each, explaining what we understand about it and how it evolved. The list is, as Lane himself admits, a bit arbitrary, and on first inspection it may give off a whiff of Scala Naturae, arranging life on a ladder from lower to higher. But once you delve into Lane’s writing, those minor qualms will evaporate. Lane, the author of two previous books about biology, writes about tricky topics like the chemistry of photosynthesis with grace and ease. On the topics I’m familiar with, I can vouch that he has picked good studies to showcase. Lane is also a scientist himself, and he not only reports on the latest research on each topic but also sometimes steps in with intriguing ideas of his own.

As with future posts of this ilk, this is not a full-blown book review. Call it a book (p)review: a heads-up about a book that has grabbed my attention. While I started reading Life Ascending for work, I look forward to finishing it for my own enjoyment.

The Kyoto Prize has gone to Peter and Rosemary Grant, I see from 80 Beats. Congratulations to them both for this Nobel-esque honor. If you don’t immediately recognize their names, you can start with this post I wrote last fall about the Grants’ research on the evolution of Darwin’s Finches, and then finish up with a couple books: their own How and Why Species Multiply: The Radiation of Darwin’s Finches and the Pulitzer-Prize winning The Beak of the Finch: A Story of Evolution in Our Time by Jonathan Weiner.

More and more, scientists are figuring out the molecular changes that have taken place over the course of our evolution. It’s one thing, however, to have a good idea of the ways in which our DNA was altered, but it’s quite another to figure out how those changes affected our ancestors, and how those changes may have spread from an individual to the entire species through a process such as natural selection.

Knowing how genes work makes it possible to come up with hypotheses about how changes to those genes evolved. And today scientists can engineer animals to see if those hypotheses hold up. A couple years ago I blogged about a study on the evolution of our color vision, in which scientists gave mice the power to see the colors that we (and other primates) can see. Now comes a similar study on the evolution of language. The mice involved may not be able to talk, but their brains have changed in some very interesting ways.

This story begins with a family in London who had trouble with language. Some members of the family had trouble speaking and understanding grammar. They turned out to have an inherited language disorder, and scientists were able to use the family’s genealogy to pinpoint the gene involved, which they dubbed Foxp2. Foxp2 encodes a transcription factor, a protein that switches other genes on or off. That can make a gene very powerful, but it can also make it hard for scientists to figure out what it does, since its ultimate effects on a person’s body must first be carried down through a cascade of other genes. But it’s pretty clear at this point that Foxp2 influences the development of the brain.

Foxp2 exists in other animals, and in many cases it appears to have an influence on communication. When scientists have knocked out the gene in mouse embryos, for example, the mice are born having trouble producing the ultrasonic squeaks they need to make in order to get help from their mother. In 2002, Wolfgang Enard of the Max-Planck Institute for Evolutionary Anthropology and his colleagues compared the version of Foxp2 in humans to other animals and found that it had undergone a dramatic evolution in our own ancestry after our ancestors branched off from those of chimpanzees and bonobos. Our hominid ancestors aquired two mutations to the gene that each changed an amino acid in the Foxp2 protein. In 2007, Max Planck researchers announced that they had found the Foxp2 gene in the DNA of Neanderthals, our closest hominid relatives. It turned out they shared that same altered sequence. If Neanderthals share our version of Foxp2 thanks to common descent, that means that the two amino acids changed before our common ancestors split off, some 800,000 years ago. It presumably was one of many changes that took place to many genes in our hominid ancestors on the road to full-blown language.

To get a sense of how this new version of Foxp2 might have changed the brains of our ancestors, Enard and his colleagues have now tweaked Foxp2 in mice into a human form. Because Foxp2 has changed very little in mammal evolution (except in humans), a mouse version of Foxp2 is a fairly good model for what the gene looked like in our own ancestors. And so this experiment can, in very rough form, replay the transition from the old Foxp2 to the new.

As the scientists report in Cell tomorrow, the mice are generally healthy, but their behavior has changed. Their squeaks are lower in frequency. They explore less. They have less dopamine in the brain, a neurotransmitter that we need to control our bodies and to pursue rewarding things like food. Dopamine is produced in the base of the brain by a clump of neurons called the basal ganglia.

Scientists who have studied people with Foxp2 defects have noticed that part of the basal ganglia, called the striatum, is altered. So the researchers looked closely at the striatum of the humanized mice. They discoverd that certain kinds of neurons had longer branches and could sprout new connections with other neurons than in regular mice.

None of these changes should be accepted blindly as having happened in our own ancestors. The effect of a mutation to a gene depends a lot on the other genes it interacts with. When Foxp2 changed in our ancestors, it was interacting with many other hominid genes, not with genes in mice.

Nevertheless, there are many intriguing clues from this study that hint that perhaps these mice are pointing to at least a few changes that gave rise to language. It turns out, for example, that people who produce less dopamine in the basal ganglia do a better job of breaking down the sounds of speech into smaller chunks in the brain in order to undertand the words someone is saying. It’s also intriguing that songbirds have independently evolved Foxp2 as they’ve become excellent singers, and when scientists block Foxp2 expression in the basal ganglia of birds, they do a worse job of singing.

Obviously, mice are no better at singing like birds than they are at talking like us. But it’s possible that their brains have been tweaked in a crucial way, much as happened independently in the ancestors of both birds and people.

Source: Enard et al.: “A Humanized Version of Foxp2 Affects Cortico-Basal Ganglia Circuits in Mice.” Cell 137, 961–971, May 29, 2009. DOI 10.1016/j.cell.2009.03.041 www.cell.com. Publishing in

Thanks to everyone who’s voted so far on the cover for The Tangled Bank. As of Monday evening, 641 people have voted. That’s not a focus group–it’s a focus army. If you haven’t voted yet, please do–I’ll check in from time to time to see how the pie slices morph.

The results are interesting. A whale cover (Whale1) is in the lead, with 22% of the vote. Wasp1 comes in second (21%), and Tiktaalik1 (18%) comes in third. Clearly, no huge conquests in this poll. But if you tally up the covers by beast, the ranking flips. Combined, All the Tiktaalik covers got 38% of the vote, the wasps got 35%, and the whales got 28%. I’m sure there are all sorts of psychological artefacts at play here, but I’m still intrigued at how all-over-the-board the results are.

Fortunately, many of you were also ready to share opinions about the covers, including some who were not satisfied with any of them. (I neglected to add a “None of the above” choice.) A number of people complained that the covers don’t speak to the title, “The Tangled Bank,” which is a phrase Darwin uses in his marvelous close of The Origin of Species, when he writes of the diversity into which life has evolved. The tricky thing about pictures that convey diversity is that they can sink into visual incoherence. That’s the last thing you want on a cover. But I hear you, and I’m going to work more on this with my publisher.

[Update 4:30 pm: I left off one of the covers (Tiktaalik3) from the original poll. You can re-vote now.]

Greetings, readers. I write to you from that frenzy towards the end of writing a book when everything has to be done at once and the sight of the incoming pincers makes me freeze like a deer in the…pincers. See, I can’t even come up with a good metaphor right now.

As some of you may recall, I’m writing a non-majors textbook called The Tangled Bank: An Introduction to Evolution. The book includes the nuts and bolts of selection and drift, along with the origin of complex traits, coevolution, sex (lots of sex), medicine, human behavior (and nonhuman), and the fearsome hand of extinction. It’s going to be heavily laden with cool examples from recent years, from E. coli that break all the rules to kinky ducks. If all goes according to plan, it should be out in time this fall for the 150th anniversary of the publication of The Origin of Species (but, of course, you can pre-order right now).

Right now, I’m signing off on the final proofs for the book and wishing that all scientists would agree to a moratorium on the publication of any interesting new research on evolution for, say, the next two years. And I’m also trying to decide on a cover. I always find this an agonizing process, perhaps because I’m not in touch with my inner designer. So I’d love to get your opinion. Take a look at these eight covers and then vote at the bottom of the post for the one you like. My goal with this book has been to create something that will not only serve well as a textbook but will also be a good read for anyone who wants to get a handle on evolution in the twenty-first century. So I want to avoid a cover that’s too textbooky. (Note that the final covers will, of course, not be watermarked)

The first two (Whale1 and Whale2) are paintings by Carl Buell of Ambulocetus, an ancient relative of today’s whales and dolphins.

The next three (Tiktaalik1-3) are also by Buell. These are of Tiktaalik, a species that lived during the emergence of four-legged land vertebrates from fish.

The last is of a wasp that has been fooled by an Australian orchid into thinking the flower is a female wasp–fooled so far as to actually complete the full act of wasp love. With a vague invertebrate sense of dissatisfaction, the wasp flies off, carrying orchid pollen, which it will deposit on its next bad date. It’s a great story (which I describe at length in the book), but you wouldn’t be able to guess it from this lovely photo.