Mole rats are a pretty ugly, obscure bunch of creatures. They live underground in Africa, where they use their giant teeth to gnaw at roots. Those of you who know anything about mole rats most likely know about naked mole rats, which have evolved a remarkable society that is more insect than mammalian, complete with a queen mole rat ruling over her colony. But according to a paper in press at the Journal of Human Evolution, mole rats are important for another reason. Their evolution and our own show some striking parallels that may shed light on how our ancestors diverged from other apes.

The authors of the paper, Greg Laden of the University of Minnesota and Harvard’s Richard Wrangham, believe that the rise of hominids was marked by a shift in food. Reviewing the evidence from fossils and living apes, they argue that common ancestor of humans and our three closest relatives (chimpanzees, bonobos, and gorillas) dwelled in a rain forest. If this ancient ape was anything like living chimps and gorillas, it depended mainly on fruits. When it couldn’t find fruits, it turned to other so-called “fallback foods” such as soft leaves and pith.

Judging from the fossils of plants and animals found alongside early hominid bones, it seems that hominids shifted from dense rain forests to woodlands, and much later to open, arid savannas. It would have been harder to survive on the diet of a gorilla or a chimpanzee in such places. Laden and Wrangham point out that in Gabon, gorillas that live in rainforests don’t venture into the surrounding savannas, despite the fact that the savannas get a lot of rain. The problem is that outside of rainforests, there just aren’t enough of their fallback foods to sustain them.

So how did hominids survive? Laden and Wrangham argue that they began to rely on a new fallback food: roots, tubers, and other “underground storage units.”(To me this term sounds too much as if it came from a subterranean Ikea catalog, so I’ll just use the word tubers.) The idea was first proposed in 1980 by other scientists who observed that one important difference between hominids and other apes is their teeth. Chimpanzees and gorillas have shearing edges on their teeth that help them slice up leaves. Hominids had teeth that resembled those of pigs and bears, which can chew tough, fiber-rich food. Pigs dig up tubers with their snouts, bears with their claws. Fossil discoveries suggest that hominids might have used sticks or horns. But they all chewed the tubers in much the same way.

In the new paper (posted by Laden here), Laden and Wrangham explore this idea in much more detail. They point to evidence that tubers are more diverse in savannas than in rain forests, and grow at densities that can be hundreds of times higher. This makes intuitive sense when you consider that tubers are probably adaptations to dry, unpredictable climates where plants need to store away energy underground. In the stable dampness of a rain forest, there isn’t much use for a tuber. Laden and Wrangham also point out that human foragers who live where lots of tubers grow take advantage of them. They prefer other food, like ripe fruits, but in tough times they dig up their meals.

Laden and Wrangham then turn from the present to the past. If their hypothesis is right, hominids must have lived in places where they might have eaten tubers. That’s a tricky question to answer directly for most sites where hominid fossils have been found, because scientists haven’t found enough plant fossils associated with them.

Enter the mole rats.

Mole rats love tubers, and where you find mole rats, you generally find a lot of tubers for them to gnaw on. What’s more, mole rats and humans have a taste for many of the same species that produce underground storage units. Mole rats have left a long fossil record in Africa since they first appeared some 20 million years ago–not coincidentally when tuber-rich habitats may have begun to spread through Africa.

Laden and Wrangham predicted that hominids and mole rats should tend to have left fossils in the same habitats. They looked at fossil sites from six million years ago to half a million years ago in eastern and southern Africa, where hominids lived. They then picked out sites where either hominids or mole rats had been found, or both. Of the 21 sites that had mole rats, 17 also had hominids. Less than a fifth of the sites without mole-rats had hominid fossils. The pattern suggests that mole-rats and hominids both evolved to take advantage of the rich supply of tubers in African savannas. They came at the tubers from below, we from above.

Dribs and drabs of this hypothesis have trickled out over the past six years. In a 1999 paper in the journal Current Anthropology, Laden and Wrangham and their colleagues suggested that tubers were important to hominids and then became really important about 1.9 million years ago. At that time, hominids began emerging who were much taller and bigger-brained than their ancestors, and who also had smaller teeth. Laden and Wrangham argued that hominids at this time must have discovered fire, which would have allowed them to cook down tubers, liberating much of the nutrition in them. In this 2002 article Natalie Angier offers a nice summary of their thinking at the time—along with the skeptical reaction it drew from some experts. One big problem is that the oldest good evidence for fire is only a few hundred thousand years old, not almost two million.

The new paper doesn’t address the skepticism about this later part of their scenario. Instead, it looks back at the first four million years of our life with tubers. Laden and Wrangham propose testing their hypothesis by looking at the trace elements and isotopes in tubers to see if the patterns are reflected in the composition of hominid fossils. I also wonder about how they got hold of the tubers. Were the earliest hominids able to fashion digging sticks, or were they merely using their hands, the way savanna baboons do today? How exactly, I wonder, did we get to be the upright mole rats?

(Update: 8/15 10 am: Thanks to Hoopman for pointing out some new findings that may show evidence of fire 1.5 million years ago. Here’s a BBC article with some details. As far as I can tell, though, the results have only been presented at a conference. They haven’t been published in a journal.)

It’s bad enough to see basic scientific misinformation about evolution getting tossed around these days. USA Today apparently has no qualms about publishing an op-ed by a state senator from Utah (who wants to have students be taught about something called “divine design”) claiming there is no empirical evidence in the fossil evidence that humans evolved from apes. I’m not sure what we’re supposed to do with the twenty or so species of hominids that existed over the past six million years. Perhaps just file them away under “divine false starts.”

But history takes a hit as well as science. Creationists try whenever they can to claim that Darwin was directly responsible for Hitler. The reality is that Hitler and some other like-minded thinkers in the early twentieth century had a warped view of evolution that bore little resemblance to what Darwin wrote, and even less to what biologists today understand about evolution. The fact that someone claims that a scientific theory justifies a political ideology does not support or weaken the scientific theory. It’s irrelevant. Nazis also embraced Newton’s theory of gravity, which they used to rain V-2 rockets on England. Does that mean Newton was a Nazi, or that his theory is therefore wrong?

Creationists are by no means the only people who are getting history wrong these days. Yesterday in Slate, Jacob Weisberg wrote an essay in which he claimed that evolution and religion are incompatible. He claims to find support for his argument in Darwin’s own life.

That evolution erodes religious belief seems almost too obvious to require argument. It destroyed the faith of Darwin himself, who moved from Christianity to agnosticism as a result of his discoveries and was immediately recognized as a huge threat by his reverent contemporaries.

I get the feeling that Weisberg has yet to read either of the two excellent modern biographies of Darwin, one by Janet Browne and the other by Adrian Desmond and James Moore. I hope he does soon. Darwin’s life as he actually lived it does not boil down to the sort of shorthands that people like Weisberg toss around.

Darwin wrestled with his spirituality for most of his adult life. When he boarded the Beagle at age 22 and began his voyage around the world, he was a devout Anglican and a parson in the making. As he studied the slow work of geology in South America, he began to doubt the literal truth of the Old Testament. And as he matured as a scientist on the journey, he grew skeptical of miracles. Nevertheless, Darwin still attended the weekly services held on the Beagle. On shore he sought churches whenever he could find them. While in South Africa, Darwin and FitzRoy wrote a letter together in which they praised the role of Christian missions in the Pacific. When Darwin returned to England, he was no longer a parson in the making, but he certainly was no atheist.

In the notebooks Darwin began keeping on his return, he explored every implication of evolution by natural selection, no matter how heretical. If eyes and wings could evolve without help from a designer, then why couldn’t behavior? And wasn’t religion just another type of behavior? All societies had some type of religion, and their similarities were often striking. Perhaps religion had evolved in our ancestors. As a definition of religion, Darwin jotted down, “Belief allied to instinct.”

Yet these were little more than thought experiments, a few speculations that distracted Darwin every now and then from his main work: of discovering how evolution could produce the natural world. Darwin did experience an intense spiritual crisis during those years, but science was not the cause.

At age 39, Darwin watched his father Robert slowly die over the course of months. His father had confided his private doubts about religion to Darwin, and he wondered what those doubts would mean to Robert in the afterlife. At the time Darwin happened to be reading a book by Coleridge called Friend and Aids to Reflection, about the nature of Christianity. Nonbelievers, Coleridge declared, should be left to suffer the wrath of God.

Robert Darwin died in November, 1848. Throughout Charles’s life, his father had shown him unfailing love, financial support, and practical advice. And now was Darwin supposed to believe that his father was going to be cast into eternal suffering in hell? If that were so, then many other nonbelievers, including Darwin’s brother Erasmus and many of his best friends, would follow him as well. If that was the essence of Christianity, Darwin wondered why anyone would want such a cruel doctrine to be true.

Shortly after his father’s death, Darwin’s health turned for the worse. He vomited frequently and his bowels filled with gas. He turned to hydropathy, a Victorian medical fashion in which a patient is given cold showers, steam baths, and wrappings in wet sheets. He would be scrubbed until he looked “very like a lobster,” he wrote to his wife Emma. His health improved, and his sprits rose even more when Emma discovered that she was pregnant again. In November 1850 she gave birth to their eighth child, Leonard. But within a few months death would return to Down House.

In 1849 three of the Darwin girls, Henrietta, Elizabeth, and Anne suffered bouts of scarlet fever. While Henrietta and Elizabeth recovered, nine-year old Anne remained weak. She was Darwin’s favorite, always throwing her arms around his neck and kissing him. Through 1850 Anne’s health still did not rebound. She would vomit sometimes, making Darwin worry that “she inherits I fear with grief, my wretched digestion.” The heredity that Darwin saw shaping all of nature was now claiming his own daughter.

In the spring 1851 Anne came down with the flu, and Darwin decided to take her to Malvern, the town where he had gotten his own water-cure. He left her there with the family nurse and his doctor. But soon after, she developed a fever and Darwin rushed back to Malvern alone. Emma could not come because she was pregnant again and just a few weeks away from giving birth to a ninth child.

When Darwin arrived in Anne’s room in Malvern, he collapsed on a couch. The sight of his ill daughter was awful enough, but the camphor and ammonia in the air reminded him of his nightmarish medical school days in Edinburgh, when he watched children operated on without anesthesia. For a week–Easter week, no less–he watched her fail, vomiting green fluids. He wrote agonizing letters to Emma. “Sometimes Dr. G. exclaims she will get through the struggle; then, I see, he doubts.–Oh my own it is very bitter indeed.”

Anne died on April 23, 1851. “God bless her,” Charles wrote to Emma. “We must be more & more to each other my dear wife.”

When Darwin’s father had died, he had felt a numb absence. Now, when he came back to Down House, he mourned in a different way: with a bitter, rageful, Job-like grief. “We have lost the joy of our household, and the solace of our old age,” he wrote. He called Anne a “little angel,” but the words gave him no comfort. He could no longer believe that Anne’s soul was in heaven, that her soul had survived beyond her unjustifiable death.

It was then, 13 years after Darwin discovered natural selection, that he gave up Christianity. Many years later, when he put together an autobiographical essay for his grandchildren, he wrote, “I think that generally (and more and more as I grow older), but not always, that an agnostic would be the most correct description of my state of mind.”

Darwin did not trumpet his agnosticism. Only by poring over his private autobiography and his letters have scholars been able to piece together the nature of his faith after Anne’s death. Darwin wrote a letter of endorsement, for example, to an American magazine called the Index, which championed what it called “Free Religion,” a humanistic spirituality in which the magazine claimed “lies the only hope of the spiritual perfection of the individual and the spiritual unity of the race.”

Yet when the Index asked Darwin to write a paper for them, he declined. “I do not feel that I have thought deeply enough [about religion] to justify any publicity,” he wrote to them. He knew that he was no longer a traditional Christian, but he had not sorted out his spiritual views. In an 1860 letter to Asa Gray—a Harvard botanist, the leading promoter of Darwin in America, and an evangelical Christian–he wrote, “I am inclined to look at everything as resulting from designed laws, with the details, whether good or bad, left to the working out of what we may call chance. Not that this notion at all satisfies me. I feel most deeply that the whole subject is too profound for human intellect. A dog might as well speculate on the mind of Newton.”

In private Darwin complained about social Darwinism, which was being used to justify laissez-faire capitalism. In a letter to the geologist Charles Lyell, he wrote sarcastically, “I have received in a Manchester newspaper rather a good quib, showing that I have proved ‘might is right’ and therefore that Napoleon is right, and every cheating tradesman is also right.” But Darwin decided not to write his own spiritual manifesto. He was too private a man for that.

Despite his silence, Darwin was often pestered in his later years for his thoughts on religion. “Half the fools throughout Europe write to ask me the stupidest questions,” he groused. The inquiring letters not only tracked him down to Down House but reached deep into his most private anguish. To strangers, his responses were much briefer than the one he had sent to Gray. To one correspondent, he simply said that when he had written the Origin of Species, his own beliefs were as strong as a prelate’s. To another, he wrote that a person could undoubtedly be “an ardent theist and an evolutionist,” and pointed to Asa Gray as an example.

Yet to the end of his life, Darwin never published anything about religion. Other scientists might declare that evolution and Christianity were perfectly in harmony, and others such as Thomas Huxley might taunt bishops with agnosticism. But Darwin would not be drawn out. What he actually believed or didn’t, he said, was of “no consequence to any one but myself.”

Darwin and and his wife Emma rarely spoke about his faith after Anne’s death, but he came to rely on her more with every passing year, both to nurse him through his illnesses and to keep his spirits up. At age 71, a few weeks before his death, he looked over the letter she had written to him just after they married. At the time she was beginning to become worried about his faith and urged him to remember what Jesus had done for him. On the bottom he wrote, “When I am dead, know that many times, I have kissed & cryed over this.”

It is a disservice to Darwin, and to history, to turn his tortured, complex life into a talking point in a culture war.

(Much of this post is adapted from the last chapter of my book, Evolution.)

I’ve got two stories in tomorrow’s New York Times about getting sick.

One is about malaria. I’ve always been fascinated by how parasites can manipulate their hosts for their own ends, and much of my book Parasite Rex is dedicated to explaining how this creepy remote control works. I’ve come across many new examples from time to time. Now a new study shows that the parasite that causes malaria can alter us humans to turn us into good mosquito bait. As with most stories about life, this one is ultimately about evolution—in this case, how parasites repeatedly have evolved ways to boost their own reproductive success by manipulating hosts like us.

I’ve never gotten malaria (knock on wood), but I have just experienced the subject of my second piece: appendicitis. Three weeks ago I got appendicitis, and if I lived 150 years ago my appendix would have probably ruptured and I’d have died. Fortunately, I got to the hospital without a hitch and had a straightforward operation to get the appendix out. Once the anesthesia cleared from my head, I began mulling how odd it was that I was born with an organ so exquisitely suited to failure and so useless to me. The manipulations of the malaria parasite are remarkable adaptations, but the appendix is, to a great extent, an maladaptation.

In the article, I offer some of the ideas scientists have had about how we all ended up with an appendix, but there was one interesting take on the appendix that I didn’t have room to include in my story. Evolutionary biologists Randolph Nesse and George Williams wrote an article a few years back in Scientific American, in which they argued that all things being equal, natural selection should favor mutations that made the appendix dwindle away to nothing. So why isn’t it gone? Perhaps if the appendix got even smaller than it is now, it would become even more prone to appendicitis and cause more deaths. Natural selection, in other words, has reached a dead end.

It’s an interesting idea, but it would take a study of thousands of people—measuring their appendix and seeing who does or doesn’t get appendicitis—to test it. Perhaps some philanthropist will get appendicitis some day and decide to drop a few million bucks to figure out how exactly we all got stuck with this peculiar little time bomb.

I’ll close the week with an open letter to President Bush just released by the American Astronomical Society’s president, Prof. Robert Kirschner, to express disappointment with his comments on bringing intelligent design into the classroom. Astronomers may not deal with natural selection or fossils, but as a general principle, they don’t like seeing non-science and science getting confused.

Washington, DC. The American Astronomical Society is releasing the text of a letter concerning “intelligent design” and education that was sent earlier today to President George W. Bush by the President of the Society, Dr. Robert P. Kirshner.

Robert P. Kirshner
President, American Astronomical Society
Harvard College Professor and Clowes Professor of Science at Harvard University

A statement from the National Science Teachers’ Association on Bush’s remarks about Intelligent Design:

NSTA Disappointed About Intelligent Design Comments Made by President Bush
2005-08-03 – NSTA

NSTA strongly supports the premise that evolution is a major unifying concept in science and should be included in the K-12 education frameworks and curricula. This position is consistent with that of the National Academies, the American Association for the Advancement of Science, and many other scientific and educational organizations.

The American Geophysical Union just issued a press release in response to Bush’s comments about intelligent design. It’s not online at their web site yet, so I’ve posted it here. (Update: It’s on line now.) This is not the first time that the 43,000 members of the AGU have spoken out against creationism. They protested the sale of a creationist account of the Grand Canyon in National Park Service stores, and condemned the airing of a creationist movie about cosmology at the Smithsonian Institution. But this is the first time they’ve taken on the President.

American Geophysical Union 2 August 2005 AGU Release No. 05-28 For Immediate Release

AGU is a scientific society, comprising 43,000 Earth and space scientists. It publishes a dozen peer reviewed journal series and holds meetings at which current research is presented to the scientific community and the public.

After a day-long road trip from Ohio, I finally had the chance to read the news that President Bush thinks that schools should discuss Intelligent Design alongside evolution, so that students can “understand what the debate is about.”

As Bush himself said, this is pretty much the same attitude he had towards creationism when he was a governor. His statements back in Texas didn’t actually lead to any changes in Texas schools, and I doubt that these new remarks will have much direct effect, either. But, like Chris Mooney, I’m a journalist, and like him I would have loved to have been in the crowd of reporters when Bush made these remarks.

Mooney would have asked Bush how he squares his comments with those of his own science advisor, John Marburger, who dismisses Intelligent Design out of hand. I would follow up on his question by expanding it to a much bigger scale.

Mr. President, I would ask, how do you reconcile your statement that Intelligent Design should be taught alongside evolution with the fact that your administration, like both Republican and Democratic administrations before it, has supported research in evolution by our country’s leading scientists, while failing to support a single study that is explicitly based on Intelligent Design? The National Institutes of Health, the National Science Foundation, and even the Department of Energy have all decided that evolution is a cornerstone to advances in our understanding of diseases, the environment, and even biotechnology. They have found no such value in Intelligent Design. Are they wrong? Can you tell us why?

For plenty of other comments, you can follow the links at Pharyngula

Update 8/2 7:45 pm: I might also ask the President to respond to 43,000 scientists who think he’s putting schoolchildren at risk.

Update 8/3 5:30 pm: Or 55,000 science teachers who are shocked and disappointed by his remarks.

Update 8/6 9:30 am: Or the nation’s astronomers, who think his remarks are bad for all science.

I’ve been on hiatus for quite a while, in part because of some surgery (more on that later), but I just wanted to write a quick post to point you to my latest article in tomorrow’s New York Times, about how birds can sing like cricket. It’s a wonderful example of how sexual selection can alter bodies, not for simple survival but to lure the opposite sex.