This female praying mantis is finishing up the last tasty bits of the male that just mated with her. In the lead article in tomorrow’s science section of the New York Times, I talk to scientists who study females of some species that sometimes devour their mates. Sexual cannibalism is not common, but it is revealing. The evolutionary forces that shape the sexes can drive them into some extreme conflicts, even turning one sex into a meal for the other. In some cases, males actually become partners in their own demise–passively or complicitly. A new study indicates that male praying mantises are not so willing. They can tell when females are hungry, and they take extra precautions.

I focus on new research in my article, but the history of sexual cannibalism is just as interesting. Scientists have been debating the nature of sexual cannibalism for over twenty years, and their debates capture one of the biggest struggles over how to study evolution. I could only touch briefly on this history in the article, so let me explain here what I mean…

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Before I moved the Loom to this address earlier this year, I got a fair amount of comments on my blogs about evolution from creationists. (See this entry, for example.) They fell off after the move, but now they’re back in fine form. Today we are joined by Kevin Anderson, editor-in-chief of the Creation Research Society Quarterly.

Here’s a little background: last week I wrote here about stumbling across a radio show put out by the Institute of Creation Research. It claimed that recent research on the human genome supports Young Earth creationism. Dr. Anderson spoke on the program about how sickle-cell anemia and lactose tolerance, and other genetic changes in human populations have nothing to do with evolution but are just the result of original sin.

Dr. Anderson’s outfit is not shy about how life began. Here I quote from their “statement of belief”:

1. The Bible is the written Word of God, and because it is inspired throughout, all its assertions are historically and scientifically true in the original autographs. To the student of nature this means that the account of origins in Genesis is a factual presentation of simple historical truths.

2. All basic types of living things, including man, were made by direct creative acts of God during the Creation Week described in Genesis. Whatever biological changes have occurred since Creation Week have accomplished only changes within the original created kinds.

3. The great flood described in Genesis, commonly referred to as the Noachian Flood, was an historic event worldwide in its extent and effect.

Are we clear?

The radio show I caught was perfectly consonant with this belief. In my post, I pointed out some of the many errors and misleading statements in the show, including some made by Dr. Anderson. Well, today he has left a comment on the blog that’s a doozy.

Check it out, and check out my response in the comment thread. I’ll be curious to see where this goes…

Update: 8/1 9:50 am: I appreciate the comments that are already coming in–as always, interesting stuff. Rather than splitting comments between two posts and dispersing the conversation, could people leave all their comments on the original post? Thanks.

The language of DNA is written in a four-letter alphabet. The four different chemical units of DNA (called nucleotides) create an incomprehenisbly vast range of possibility codes. Consider a short sequence of 41 nucleotides. There are over 4.8 trillion trillion possible sequences it could take. In this vast universe of possibilities, how can natural selection hit on new DNA sequences that help life survive?

All living things have genes. Enzymes read those genes and produce a copy of their code, which a cell can then use to build a protein. But in order to read a gene, the enzymes must first lock onto a distinctive segment of DNA near the gene, known as a promoter. Promoters act like switches, which a cell can use to turn genes on and off. Different genes carry different promoters, so that they can be switched on under different conditions.

Scientists have studied the promoters of the bacteria Escherichia coli more closely than those of any other species, and they’ve identified some of its switching patterns. When Escherichia coli is growing quickly, it produces a lot of gene-reading enzymes factors called sigma 70. Sigma 70 can switch on several hundred genes that allow the microbe to feed and build up its biomass and reproduce. If Escherichia coli begins to starve, it slips into a sort of suspended animation, and produces a different enzyme factor called sigma S. Sigma S recognizes a different set of genes that begin to make the proteins necessary for shutting the microbe’s operations down.

Here we have a wonderfully precise system for controlling genes. Now imagine that Escherichia coli acquires a gene with no promoter at all–just a random sequence of DNA next to the gene, 41 nucleotides long. Imagine that this DNA starts going through cycles of mutation and natural selection. Would it be possible for a random sequence to change into one Sigma 70 could grab? Could it go from nothing to a promoter?

The answer is yes. How long would it take? According to some recent experiments, two days. Two.

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Cut-and-paste creationism?

Yesterday I pointed readers to a column attacking evolution by Jack Kemp on the web site Town Hall. Today a sharp-eyed commenter pointed out that it is almost entirely identical to a column from Phyllis Schlafly from August 16 on the Eagle Forum. I don’t know if these pages are going to be pulled down or otherwise altered if word gets out, so here’s a screengrab of Kemp and of Schlafly. It looks pretty much word for word identical to me. You be the judge…

Update 2:50 pm: I wonder if Town Hall got its columnists jumbled. This page lists Kemp’s column and a piece by Schlafly right next to one another on Monday.

Update: 3:20 pm: What’s also funny is that several commenters on Town Hall have pointed out this eerie similarity as well, but apparently to no avail…

Update: 4:00 pm: Like a radioactive tracer flowing through the bloodstream, Kemp’s column spreads now to David Horowitz’s Frontpage. [Hat tip: Darwin Central blog.)

Update: 4:20 pm: MYSTERY SOLVED. “Chris,” who calls himself “Team Lead” at Town Hall informs us that:

FYI: This is not some conspiracy. Jack Kemp’s syndicators were substituting a column by Schafly because he is on vacation. Our system received the column by Schafly under Kemp’s name automatically, and the editor who marked the column live didn’t catch that it was a guest column.

Now the column appears under Schlafly’s name. Direct your critique of the column to her.

Scoop up some dirt, and you’ll probably wind up with some slime mold. Many species go by the common name of slime mold, but the ones scientists know best belong to the genus Dictyostelium. They are amoebae, and for the most part they live the life of a rugged individualist. Each slime mold prowls through the soil, searching for bacteria which it engulfs and digests. After gorging itself sufficiently, it divides in two, and the new pair go their separate, bacteria-devouring ways. But if the Dictyostelium in a stamp-size plot of soil should eat their surroundings clean, they send each other alarm signals. They then use the signals to steer toward their neighbors, and as many as a million amoebae converge in a swirling mound. The mound itself begins to act as if it were a single organism. It stretches out into a bullet-shaped slug the size of a sand grain, slithers up toward the surface of the soil, probes specks of dirt, and turns around when it hits a dead end. Its movements are slow – it needs a day to travel an inch – but the deliberateness of the movements eerily evokes an it rather than a they.

After several hours, the Dictyostelium slug goes through another change. The back end catches up with the tip, and the slug turns into a blob. About 20 percent of the cells move to the top of the blob and produce a slender stalk. In order to keep the stalk from flopping over, these cells must produce rigid bundles of cellulose. Unfortunately, this cellulose also tears apart the amoebae that make it. The remaining amoebae in the blob then take advantage of the suicide of their slugmates. They slide up to the top and form a globe. Each amoeba in the globe covers itself in a cellulose coat and becomes a dormant spore. In this form the colony will wait until something – a drop of rainwater, a passing worm, the foot of a bird – picks up the spores and takes them to a bacteria-rich place where they can emerge from their shells and start their lives over.

The individual amoebae forming the stalk make the ultimate sacrifice so that other Dictyostelium may live and perhaps reproduce. These stalk-formers are not marked for death when they are born. When the amoebae mix together and the slug takes shape, the individuals that wind up in the front end of the slug will be the ones that form the stalk. In other words, they get a losing ticket in the Dictyostelium lottery. Aside from their rotten luck, they are indistinguishable from the amoebae that will survive as spores.

It is remarkable that stalk-forming amoebae should remain loyal to their fellow amoebae. Why should they willingly join a group of other amoebae when their loyalty will end in its and their death? Why shouldn’t amoebae just stay away from the group and try to tough it out on their own? Of course, just joining a group is not a guarantee of loyalty. It’s not hard to imagine amoebae finding a way to avoid the lottery of death. Actually, we don’t even have to imagine them: scientists have discovered that some Dictyostelium will cheat their fellow amoebae, thanks to genes that ensure that they will form spores rather than stalks.

The puzzle of loyal amoebae is, at its foundation, a puzzle about evolution. In each generation, the members of a population will vary in all sorts of ways – in their size, in their shape, and in their behavior. Depending on the environment in which the population lives, some of these variations will give certain members an edge when it comes to surviving and reproducing. Genes that make successful variations possible will become more common, while the unsuccessful genes will become less common.

Imagine that a Dictyostelium divides in two, and one of its offspring undergoes a mutation that makes it cheat. It escapes the stalk lottery, and is guaranteed to become a spore. Over generations, its descendants would become more common because none of them have to die making a stalk. Its cheating gene would become more common in the population as a result. Other individuals might also mutate into cheaters on their own, and their offspring would thrive as well. Meanwhile, genes that promote cooperation would become less common. It might be possible for Dictyostelium to continue organizing slugs and stalks if only a small fraction of amoebae cheated. But in time natural selection could produce so many cheaters that a slug would fail to produce a stalk, dooming the spores to death. As plausible as this scenario may be, scientists don’t see it happening in the real world. Dictyostelium is thriving happily in forests around the world. Clearly betrayal has not evolved to catastrophic levels. Why not?

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I’m happy to report that the eyes are back.

My third book, Evolution: The Triumph of an Idea, came out in 2001. It’s a survey of the history and cutting edge of evolutionary biology, from the origin of new species to mass extinctions, from the rise of complex life to the emergence of humans. The book explores evolutionary races between hosts and parasites, between males and females. It puts evolution in a historical context as well, showing how Darwin’s theory emerged out of the science of his time and how social and political tensions foster hostility to evolution today. Scientific American called it “as fine a book as one will find on the subject.” (More information, as well as an excerpt, can be found here.)

HarperCollins has now reissued Evolution, with a new introduction from yours truly.  I reflect on the past five years of science and politics. For the politics, I focus on the Dover intelligent design trial last fall, which brought the current controversies over how to teach evolution into sharp relief. For the science, I look at new research in human evolution, from the search for genes that make us human to new discoveries about the oldest known hominids. As these links suggest, the introduction sprang from the fertile ground of this blog. So if you want to get some more writing about evolution on the printed page rather than the computer screen–or if there’s someone you know who wants to know what all this stuff about Darwin is about–please check out the book. The official release date for the reissued edition is September 5, but Amazon will let you buy it now.

Like many parasites, a species of bacteria called Wolbachia takes charge of its own fate. Wolbachia can only survive inside the cells of its hosts–invertebrates such as this lovely common eggfly. This way of life limits Wolbachia’s opportunities for long-term survival. If Wolbachia lives inside a female insect, it can infect her eggs. When those eggs hatch and mature into adult insects, they will be infected by Wolbachia as well. But if Wolbachia should find itself in a male, it has reached a dead end. It cannot infect sperm cells, and thus it has no escape from a male host. When a male host dies, Wolbachia dies as well.

Wolbachia’s solution: kill the males before they kill you.

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I was happy to see that my post on Tuesday about the evolution of whales attracted a lot of readers. One commenter asked about seals and manatees. As other commenters kindly explained, those mammals descend from other ancestors (relatives of bears and elephants, respectively) that independently moved into the water. This transition has occurred many times since vertebrates moved on land. In some cases, the animals have adapted completely to the water (such as marine reptiles). In other cases, the transition has not been so complete. Other relatives of elephants evolved into desmostylians, sometimes called “sea-bears.” They looked like polar bears but fed on aquatic plants. (pdfs here and here) The picture here is of Paleoparadoxia, from Siberia.

And then there were the aquatic sloths. Yup–sloths. Here’s a post I wrote on their transition to the sea.

The textbook explanation of DNA goes something like this: enzymes in our cells read a stretch of DNA and convert its code into a single-stranded RNA molecule, which is then used by ribosomes as a template for building a protein. That stretch of DNA biologists call a gene. The protein it encodes drifts off to do some job–building cell membranes, maybe, or switching off other genes, and so on.

This is a fairly accurate picture–for less than two percent of the human genome. The rest of our DNA does not encode proteins. Much of it may be made up of genetic material from viruses and disabled genes. That does not mean that this genomic dark matter is all useless to us. Scientists have known for decades that some small chunks of DNA act like switches for nearby genes. Proteins grab onto these switches to prevent our cells from making proteins from the genes, or to speed up the process.

Far more mysterious, however, are segments of DNA that our cells use to build RNA, without then turning that RNA into proteins. These RNA molecules are a shadowy network of molecules that quietly control much of the activity in a cell. They can interfere with other RNA molecules, blocking the construction of proteins. In some cases, they can act like sensors, able to grab onto particular kinds of molecules. When they sense a molecule, they may then stop a gene from being copied.

Scientists don’t know a lot about this shadow network, but new experiments on it are coming out every week. And now it turns out to have been very important in our own evolutionary history. In Nature today, scientists report that the fastest-evolving part of the human genome is an RNA gene…

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Whales are beautifully ridiculous. They are majestic divers, in some cases plunging nearly two miles underwater. And yet sooner or later they must rise back to the surface to breathe air. They breathe through a rather ridiculous-looking hole on top of their head. Unlike fish, which often reproduce by spraying millions of eggs and swimming away, whales give birth to one calf at a time, which they proceed to nurse for months. Some whales are like underwater bats, shrieking through their blowholes and listening to the echoes. And perhaps most ridiculous of all are whales that turn themselves into giant filters, thanks to a ridiculous tissue called baleen.

Baleen is a giant frond-like growth that sprouts from the jaws of 11 species of whales. Baleen whales open up their toothless mouths, sucking clouds of krill and other animals. They then ram the water out with their massive tongues, trapping food in their overlapping plates of baleen. Licking off the food, they open their mouths for another gulp.

Whales are ridiculous thanks to their history.They evolved from mammals on land. Their swimming, reproduction, breathing, and other adaptations to life in water are all the result of tinkering with a terrestrial animal’s body. Fossil discoveries have documented how coyote-like mammals moved into the water about 45 million years ago and became more and more adapted to the marine life. The evolution of whales was not a single leap, however, but a long series of transitions. Even after whales had abandoned life on land, they were still not yet like whales today. None of them, for example, had baleen.

Among living whales, baleen is an all-or-nothing affair. If you’re a whale you either have baleen or you have none. All other whales are profoundly different, with teeth instead of baleen. And while toothed whales can all echolocate, baleen whales cannot. Studies on whale DNA only reinforce the sharp divide between baleen whales and other whales. All baleen whales share genetic markers not found in toothed whales. In other words, the evolutionary tree of living whales is split into two branches. Paleontologists have found many extinct members of those two branches from the past 30 million years, bearing the hallmarks of either baleen whales or toothed whales.

In a sense, then, the origin of baleen whales is as remarkable as the origin of all whales. Yet that fact does not represent a real challenge to evolution. After all, there was a time when scientists had not yet found walking whales, and now they’ve found plenty. Other scientists have meanwhile been searching for the fossils of the earliest baleen whales. And, as I’ll describe below the fold, they’ve now found a particularly interesting one: a baleen whale without the baleen.

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Can a tumor become a new form of life?

This is the freaky but serious question that arises from a new study in the journal Cell. Scientists from London and Chicago have studied a peculiar cancer that afflicts dogs, known as canine transmissible venereal tumor (CTVT) or Sticker’s sarcoma. It is a cancer of immune cells called histiocytes, and dogs typically develop grapefruit-sized tumors that disappear after a few months.

Some scientists have suggested that Sticker’s sarcoma can be transmitted from dog to dog, either by mating or by licking or touching a tumor. They noted that the tumor cells appeared to share a unique genetic marker. But skeptics noted that virus-like particles are often found in or around Sticker’s sarcoma. There’s lots of strong evidence that viruses can trigger cancers (such as cervical cancer), possibly as a strategy to spread themselves rapidly. Dogs that were struck with Sticker’s sarcoma could just be acquiring a cancer-causing virus from other dogs.

To sort out just what’s going on with this cancer, the authors of the Cell paper made a big survey of dogs with Sticker’s sarcoma, examining sick pooches from five continents. They analyzed the DNA from normal cells in the dogs, as well as the DNA from their tumors. They put the tumor cells in dishes to observe how they interacted with dog cells. The picture they got was remarkably detailed and–please allow me to use the word again–freaky.

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Last night, as my family settled into a three-hour drive home, I began scanning the AM radio dial. The tuner stopped at on a well-produced segment in which the announcer was talking about recent evolution of pigmentation genes and lactose-digestion genes in humans. This is a surprise, I thought, and I settled in for a listen. It took about twenty seconds for me to realize that this was the work of creationists. I spent the next fifteen minutes listening to the piece with jaw aslack, making sure I didn’t get so distracted I missed my exit. There is something so absorbing about the elaborate rhetorical gymnastics that creationists engage in order to square their views with new scientific evidence.

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