I recently finished watching Planet Earth, the award-winning BBC nature documentary series narrated by David Attenborough. As its title implies, Planet Earth is an effort of considerable ambition: the filmmakers set out to produce a series that would provide a survey of our world's natural grandeur and biodiversity. To a remarkable extent, I think they succeeded. Of course the full richness of Earth's biosphere could not be exhaustively chronicled, but this series touches on many of the high points. It sweeps across every region of the planet, documenting our world's remaining wildernesses and some of the more important species that live in them, in the process filming things that have never been caught on camera before. In its scientific breadth and scope, in the beauty it depicts, and in the reasons it gives us both to fear, and more importantly, to hope, Planet Earth compares favorably to Carl Sagan's Cosmos.

The series consists of eleven episodes, each of which chronicles a different type of ecosystem flourishing on our planet. Over the course of the series, we're taken from icy tundra and boreal forest to tropical jungle, from the rich shallow seas to the blackness of the ocean abyss, from soaring mountains to desolate deserts to the eerie dark worlds of the cave systems beneath the planet's surface. Each episode is fifty minutes, plus a ten-minute ending segment called "Planet Earth Diaries" that shows how some of the more difficult-to-obtain shots were filmed - a nice touch that gives one appreciation for the truly heroic dedication of the photographers who traveled to some of the most remote, wild areas of the planet, braving all manner of harsh and grueling conditions, and worked in some cases for weeks on end just to catch a few moments of action on film. Three additional episodes, collectively titled Planet Earth: The Future, make the case for conservation using footage from the series and interviews with prominent advocates for the environment.

But the focus of the show, as I said, is on the breathtaking natural beauty of our planet and the wonderful, intricate tree of life that flourishes upon it. I couldn't do justice to all the high points in this one post, but here are a few that particularly stood out to me:

• a snow leopard, one of our planet's rarest and most elusive predators, hunting twisted-horned markhor antelope in the Himalayas of eastern Pakistan - the first close-up images of snow leopards in the wild ever filmed;
• the vast precipice of Venezuela's Angel Falls, the world's highest waterfall - a sheer drop of nearly a kilometer, so high that the falling water is blown into mist before it reaches the bottom;
• Nile crocodiles exploding out of the water to grab migrating wildebeest crossing their river - the terrifying tenacity of the bull crocodiles is shown when one of them, after grabbing a wildebeest's leg in its jaws, wrestles with its unlucky prey for over an hour before finally dragging the wildebeest into the water and drowning it;
• parachute divers leaping into the sunlit shaft of Mexico's Cave of Swallows, a dizzying sheer drop deeper than the Empire State Building is tall;
• a male polar bear, starving and exhausted after a long swim in the open water of the melting Arctic, desperately attacking a herd of bull walruses;
• a spectacular sequence in which an entire pride of African lions hunts and kills an elephant;
• the elaborate courtship displays of New Guinean birds of paradise;
• a band of chimpanzees waging war on a rival tribe, slipping silently into their adversaries' territory before erupting in a furious charge of intimidating shrieks and hoots; the savage hand-to-hand fighting ends with the losers being torn apart and, in some cases, devoured by the winners;
• banded sea kraits - aquatic snakes - swimming as smoothly as eels to hunt fish among the coral reefs of the Pacific;
• Borneo's Deer Cave, where a flock of three million bats has created a guano mound the size of a large building, covered with swarming, voracious cockroaches;
• in the Azores, a school of hundreds of dolphins herding scad mackerel, working in unison to encircle their prey and drive them closer to the surface, where diving cory shearwaters soar down to share in the hunt;
• the lush communities of strange life that thrive around hydrothermal vents on the ocean floor, powered by the superheated plumes of mineral-rich water erupting from fissures in the crust, like oases in the abyssal dark. When these vents stop erupting, a whole community can collapse from vibrant life into a dead, frozen forest of tube-worm skeletons - a devastation treated by the film with all the gravity of an empire's fall;
• a vast flock of migrating Baikal teal - hundreds of thousands of birds, all flying in unison - and the camera pulls back, and back, and still further back, until each individual bird is just a tiny speck, and still the whole flock cannot fit on the screen at once;
• and last but not least, time-lapse shots of the seasons changing, even time-lapse shots from space that show rivers flood, forests turn green, snow and glaciers advance - I don't know how these were taken or whether they were special effects.

The one caveat I would offer is that Planet Earth is a nature documentary, which means most of the sequences are of animals doing what animals normally do in the wild. If you're the kind of person who finds that boring, you'll probably be bored by this as well. There are plenty of hair-raising moments, but the purpose of the show is not to keep viewers constantly on the edge of their seat. Personally, I found it a spectacular glimpse of some of the Earth's last remaining places of wild beauty. If that description appeals to you, then I can safely say that you'll love Planet Earth, and I would definitely recommend it.

By now, I assume, the entire blogosphere has heard about the public-relations fiasco which the producers of the creationist film Expelled have brought upon themselves. If you haven't, here's a brief rundown: last week, everyone's favorite fire-breathing atheist blogger and biology professor, P.Z. Myers, went to see an advance screening of the film. It seems only fair that he'd get to see it - he was deceived into appearing in it by the producers, who told him it was going to be called Crossroads and would be an exploration of the relationship between science and religion, not the hardcore anti-science polemic it turned out to be. But while he was standing in line at the theater, he was met by security, who demanded he leave the premises immediately. It turned out the film's producers didn't want him to see it. But in the grandest stroke of irony ever, Myers' guest - who is also interviewed in the film, and whom the producers apparently did not recognize - was allowed in to see it. That guest? Richard Dawkins.

Mark Mathis, the producer of Expelled, has rapidly cycled through excuses in the past several days trying to explain this. First it was alleged that P.Z. Myers was being disruptive (a lie), then it was alleged that he was gate-crashing a private screening (also a lie; there was an open registration on the internet for anyone who wanted to attend). Finally, he seems to have settled on the ad hoc excuse that he simply wanted Myers to pay to see it. Apparently, Mathis is oblivious to the hypocrisy of making a film which asserts that dissenters are being unfairly shut out of scientific discourse, then banning people whom he disagrees with from seeing it and threatening them with arrest if they don't comply. (A post filed on another screening of Expelled reports that Mathis is still threatening people with expulsion for asking too many non-supportive questions. The producers have also tried to make critics sign non-disclosure agreements in an apparent bid to prevent them from writing negative reviews.)

By most accounts, Expelled is a remarkably shoddy piece of filmmaking. Its entire premise is that evolution led directly to the Holocaust, making its case by showing footage of scientists followed by footage of Nazi death camps. Of interest, it also drops the flimsy pretense of intelligent design being "science", instead claiming repeatedly and straightforwardly that ID is religious. The film's strategy of marketing directly to churches and homeschoolers ties in with that. (I really, really hope some Christian group congratulates the film's narrator, Ben Stein, on how many souls his wonderful movie is bringing to Christ. Stein is Jewish, incidentally.)

All in all, this affair has proved to be a wonderful piece of good news for friends of science. This whole affair has made the creationists look like hypocrites, and not only that, it's shone a light on the shoddy and deceptive tactics of their film and the ID movement as a whole, the very outcome they were hoping to avoid. How could this have turned out any better?

However, at least one non-creationist thinks this is somehow a disaster for us. Anyone care to guess who?

As long as Dawkins and PZ continue to be the representative voices from the pro-science side in this debate, it is really bad for those of us who care about promoting public trust in science and science education. Dawkins and PZ need to lay low as Expelled hits theaters. Let others play the role of communicator, most importantly the National Center for Science Education, AAAS, the National Academies or scientists such as Francis Ayala or Ken Miller. When called up by reporters or asked to comment, Dawkins and PZ should refer journalists to these organizations and individuals.

If Dawkins and PZ really care about countering the message of The Expelled camp, they need to play the role of Samantha Power, Geraldine Ferraro and so many other political operatives who through misstatements and polarizing rhetoric have ended up being liabilities to the causes and campaigns that they support. Lay low and let others do the talking.

The above piece of condescending concern trolling is courtesy of Matt Nisbet, the "framing" proponent who's only ever offered one piece of advice: namely, telling atheists to shut up and not voice their views or criticize religion. He's done this before, but this latest statement is by far the most arrogant and obnoxious one he's offered.

Nisbet's attitude seems to be that religious believers are overwhelmingly powerful, their opinions cannot be changed, and thus we must genuflect to them or else. His above post is of a piece with a long line of writings he's produced urging atheists to go back into the closet and hide - a ridiculous piece of advice which, I'm happy to say, has been treated with the contempt it deserves.

Nisbet's piece says bluntly, "It's Time To Let Others Be the Spokespeople for Science", with a prominent photo of P.Z Myers and Richard Dawkins. This claim displays a serious misunderstanding of what is going on here. Nisbet seems to assume that this position is some kind of mantle that can be passed from person to person. What he hasn't grasped is that, to whatever extent Myers and Dawkins are viewed as influential scientists whose opinions are worth listening to, they earned that authority by their own effort. They are doing just what they've always done - writing, speaking, publishing their opinions. Their following was not bestowed upon them from on high; they created it for themselves by presenting persuasive arguments that won people over. In other words, they're winning the battle of ideas, and Nisbet is not. His ridiculous call for them to shut up and hand that authority over to him is really just a plea for him to be handed the acclaim that he's failed to achieve by his own effort. The similarities with creationists are instructive.

Nisbet's post also displays what I call "the myth of the silenced middle": the notion that there's some reasonable, moderate center that's being drowned out by those on both extremes. The truth of the matter is that no one is being prevented from speaking their minds exactly as they wish. If Nisbet can't hear this mythical centrist majority, perhaps it's because they're not speaking out - and I agree that they're not, which is precisely why we radical, uncompromising atheists have arisen in the first place. We're tired of the fundamentalists shoving government and the media around without anyone standing up to them forcefully or effectively. We believe people's minds can be changed, and we intend to do just that. The vested interests of religion have not silenced us. I can assure Matt Nisbet that his comparatively feeble efforts are not going to succeed either.

UPDATE: Further thoughts.

Anointing the Sick

The New Testament's Book of James gives some very unusual instructions on how to treat illness:

"Is any sick among you? let him call for the elders of the church; and let them pray over him, anointing him with oil in the name of the Lord: And the prayer of faith shall save the sick, and the Lord shall raise him up; and if he have committed sins, they shall be forgiven him."

—James 5:14-15

In eras when human knowledge was far less advanced, it's not surprising that people would turn to superstitious practices such as prayer and anointing with oil in an attempt to cure illness. What's far more surprising is how many people still believe in these practices today, despite our far more advanced knowledge of scientific medicine, as well as ample evidence that faith healing does not work.

The Greek Orthodox Church, for example, makes anointing a regular practice, and claims that it offers physical healing:

At the conclusion of the service of the Sacrament, the body is anointed with oil, and the grace of God, which heals infirmities of soul and body, is called down upon each person.

...The Sacrament of the Unction of the sick is the Church's specific prayer for healing. If the faith of the believers is strong enough, and if it is the will of God, there is every reason to believe that the Lord can heal those who are diseased.

The Assemblies of God says the same thing:

In the Assemblies of God we believe neither the laying on of hands nor anointing with oil is indispensable for healing, for often in Scripture healing takes place without either. But at times the touch of a praying person and the application of oil are an encouragement to faith, and such a practice is enjoined by Scripture (James 5:14-16).

And, as Jeffrey Shallit reports, Prof. Clifford Blake of the University of Waterloo is an unabashed believer in faith healing through anointing and other, equally mystical methods:

Some people believe healing was only in the time of the Bible. But he knows it is happening now. When he began to use healing oil, he got more consistent results.

Granted, there are also Christians who believe the anointing is merely symbolic. And the reason they believe that should be obvious: because it is abundantly obvious, to those who know how to think critically, that anointing people with oil is not an effective method of curing illness. If there was any evidence that this was an efficacious treatment, we can be sure it would be universally employed in every Christian church, and would not be explained away as symbolic. But as scientific medicine has progressed and our ability to work real cures has increased, superstitious practices like this have become increasingly superfluous and have gradually faded away (although, as shown, there are still plenty of holdouts).

Certainly, the Bible's description of this does not seem like mere symbolism: it says clearly that "the prayer of faith" will save the sick, and in conjunction with the oil, "the Lord shall raise him up" (the Greek word, egeiro, means "to cause to rise", i.e., from a seat or a bed). My question to modern believers who view this passage symbolically is, if you know this doesn't work, how do you know that - and do you apply that same standard to the rest of the Bible? And to those who still use faith healing and dabs of magical oil, in an age of genetic manipulation, transplant surgery and antibiotics, my question is: Do you really believe that?

Other posts in this series:

• Do You Really Believe That?

Some news from earlier this year you might have missed: James Randi is officially ending his million-dollar challenge to those who claim they have psychic or supernatural powers. The challenge will be offered for two more years, and assuming no one succeeds and claims the money, will be terminated in March 2010.

It's not hard to see why Randi would do this. After ten years without a single successful applicant, I think he's made his point. Unsurprisingly, the best-known, most prominent psychic pretenders (Sylvia Browne, John Edward, etc.) have refused to even come near the challenge. The people who do apply are usually either recalcitrant and uncooperative or obviously mentally disturbed, in either case forcing Randi's staff to spend inordinate amounts of time and effort trying to get them to commit to a clear, testable claim. Here are some typical applications from the JREF's blog:

There are alternate versions of myself in different types of highly evolved states that work interchangeably to form the time process in its phasic reflective capacitations of experiential transience.

I want to show the matrix. To prove solutions and cures are withheld. Prove manipulations of sinister intent exist.

This money can be more effectively used to promote the causes of scientific inquiry and skepticism, rather than being held in trust while its caretakers try to sort through this river of nonsense. If there were any prospect that high-profile psychic claimants would agree to be tested, then I would encourage the challenge to continue, since debunking their claims in a major public forum could attract attention and interest that would greatly advance the skeptics' cause. But of course, these famous psychic pretenders know full well that this would be the outcome, and so they steadfastly avoid Randi's challenge. From their perspective, sad to say, it's a rational decision: why risk near-certain exposure and embarrassment by going up against a canny skeptic, when they can make comparable sums by safely exploiting the credulous and the gullible?

Interestingly, Randi's challenge is not the only one of its kind. The Skeptic's Dictionary lists numerous similar challenges offered by skeptical groups around the world. So, to handle the inevitable flood of flimflam artists who will step forward just after the challenge ends and announce that they could have won it, I advise pointing them to one of these challenges instead. A person who could win one or several of them would have an excellent claim for having their powers scientifically validated. Randi has also said, I believe, that he'd consider temporarily resurrecting the challenge if a famous psychic wanted to apply - so we can rest assured that woo-woo advocates will not be able to wriggle away from those pesky requests for proof, either now or in the years to come.

Human beings, like all other species on this planet, have a history. We came into existence through a process of slow, grinding trial-and-error, occurring over geological time via the sieve of differential survival. And like all species, our bodies and our genes reflect and bear witness to that history. Far from being perfect, one-time creations, we still bear the scars of the evolutionary process that made us.

This post will discuss some of the lines of evidence which hint at humanity's past. I won't repeat that well-known example of an evolutionary vestige, the human appendix. Instead, I'm going to focus on a few other examples that aren't as widely discussed.

• Toes. It's only because we're used to having toes that we don't usually consider how strange they are. Why do our feet have these stubby, non-functional digits on the ends? They can't grip nearly as well as fingers, and we don't need them to balance or to walk. (Why not just have a fused front of the foot?) By contrast, anyone who observes other primate species can see that they have, not two hands and two feet, but four hands, all of which are good for grasping. As human beings gained the ability to stand and walk upright, our feet lost their grasping function, but the digits themselves, though now shrunken and largely useless, remain.

• Lanugo. This little-known developmental phenomenon is an important clue to our mammalian past. Lanugo is a coat of fine, downy hair that fetuses grow while in the womb, covering the entire body except for the soles of the feet and the palms of the hands. Typically, lanugo is shed by the seventh or eighth month of pregnancy, although premature infants may retain it for several weeks after birth. The question is why we grow it at all, and the theory of evolution can easily explain this as a vestigial characteristic retained from our furry ancestors.

• Goosebumps. Fitting neatly together with lanugo is the vestigial human trait called the pilomotor reflex. When a person is cold or frightened, tiny muscles at the base of each hair contract, causing body hair to stand on end. In animals with thicker fur, this is a useful reflex: erect hairs trap air to create a layer of insulation, and they also make the animal appear larger and more intimidating. In humans, however, it is pointless. Like lanugo, goosebumps are a giveaway clue indicating that relatively hairless human beings are descended from furry progenitors.

• Hiccups. Yes, hiccups are a sign of humanity's evolutionary past. In fact, unlike goosebumps or lanugo, which merely point to our shared history with hairier mammals, hiccups point all the way back to the time when humanity's ancestors were amphibians. According to this article by Neil Shubin (HT: The Panda's Thumb), the hiccup reflex is controlled by an area of the brain that we share with tadpoles. The hiccup consists of a sharp inhalation followed by a closing of the glottis (the valve at the top of the windpipe). In tadpoles, which have this same reflex, the inhalation draws water into the mouth, where the gills can process the oxygen it contains, but closes the glottis so the water does not enter the lungs. For tadpoles, it's a vital breathing reflex; in humans, it's a hiccup. And the same measures that often arrest hiccups in human beings (inhaling carbon dioxide, stretching the chest wall by taking a deep breath) also stop the gill-breathing reflex in tadpoles.

• The true human tail. One of the most shocking - for creationists, anyway - human atavisms is the true human tail. On rare occasions, human infants are born with short, non-prehensile, but undeniably real tails, up to several inches in length and containing nerves, blood vessels, muscle fibers, and sometimes even extra vertebrae. They can move through voluntary muscle contraction.

In fact, all human embryos grow tails while in the womb, and normally they are reabsorbed before birth. The true human tail is the result when this does not happen. Usually they are surgically removed, although they are benign. For an evolutionary scientist, the reason why we grow them is obvious: we are descended from an ancestor species which had them. For creationists, who claim that human beings were created complete and separate as we currently are, it must be difficult to explain why we have so many vestigial structures that link us to other species of mammals.

• The fused chromosome 2. It's long been known that human beings have 23 pairs of chromosomes, while the other great apes such as gorillas and chimpanzees have 24. It is all but impossible that the lineage that led to humans could have completely lost all this genetic material and still produced a viable organism. Where, then, did the extra chromosomes go?

Chromosomes are tipped with distinctive segments of DNA called telomeres and have another special segment called a centromere in the middle. Lo and behold, human chromosome 2 has a telomere on one end, then an inactivated centromere, then a segment of telomeres in the middle, then another centromere, then a final telomere - the structure we would expect to find if two chromosomes had fused into one. When we compare this chromosome to the two appropriate ape chromosomes, we find a compelling match, indicating that this chromosomal fusion occurred at some point after the human lineage split from our ape relatives.

• The vitamin C pseudogene. Unlike most mammals, human beings can't synthesize their own vitamin C; we must ingest it as part of our diet, or else we get the disease of scurvy. Under the hypothesis of special creation, humans were created this way from the beginning, so we wouldn't expect evidence that we once had this ability but have since lost it. However, according to evolution, we are descended from other mammals, and since most mammals can make their own vitamin C, we'd expect that human ancestors did have this ability at some point as well. If this is so, our genes may preserve evidence of it.

Sure enough, human beings have a version of the vitamin C synthesis gene, but ours is "broken", disabled by mutations. Our primate relatives, who also lack this ability, also have broken versions of the gene. Just as evolutionary theory would predict, the same disabling mutations that exist in the human gene can be found in the genes of chimpanzees, orangutans, and macaques - compelling evidence that we are all descended from a primate common ancestor who incurred this mutation at some point in the past. (It's likely that this mutation wasn't selected against because all primate diets are rich in fruit, providing abundant vitamin C.)

Taken together, the scars of evolution provide abundant evidence of humanity's history. Like all species on this planet, we are not unique special creations. We are one end result of a long process of mutation sieved through selection, a countless series of adaptive compromises and tradeoffs. Our very bodies testify to the natural forces that have shaped us through the vast expanses of time.

You've just been to the doctor, and she has some bad news. There's a deadly new disease sweeping the population - one which strikes 1 out of 100 people and invariably kills everyone who catches it. Medical science has developed a test that is 95% accurate during the incubation period: that is, when given to someone who has the disease, it correctly returns a positive result 95% of the time, and when given to someone who does not have the disease, it correctly returns a negative result 95% of the time. Your test results have just come back positive. Are you doomed?

Before I say anything more, a simple exercise: Based on the facts I just gave, estimate the probability that you actually have the disease. A detailed calculation isn't necessary - just write down what you think the general neighborhood of the number is.

So, a 95% accurate test has indicated that you have this 1-in-100, invariably fatal disease. Should you feel terrified? Should you feel despair? Should you call your lawyer and start making out your will?

Nope. In fact, you should be optimistic. The probability that you actually have the disease is only about 16%.

Did you write down 95%, or something in that range? If so, you're probably not alone. That's the common answer. But without an education in statistics, human beings are not very good at calculating conditional probabilities off the cuff. To see where your unexpected reprieve came from, we have to consider a famous statistical principle called Bayes' rule.

Named for its discoverer, the 18th-century mathematician Thomas Bayes (also a Christian minister, ironically), Bayes' rule is a theorem for calculating conditional probabilities. In other words, if you have two possible events, A and B, each with its own independent probability, and you know the probability of B given A, Bayes' rule is the formula for determining the probability of A given B.

This may sound abstract, so let's frame it in terms of concrete events rather than variables. Let's say that A is the probability of catching the deadly disease I mentioned earlier. That's 1 out of 100, or in other words, 1%. We can write that as 0.01 for convenience.

Let's also say that B is the probability that your test results came back positive. This is a little more complicated to calculate, but we'll come back to it. We know the probability of B given A - given that you actually have the disease, the probability of a positive test is 95%, or 0.95. What you really want to know is the probability of A given B - the probability that you actually have the disease, given a positive test result.

Here's what Bayes' rule says (read "|" as "given"):

P(A|B) = ( P(B|A) * P(A) ) / P(B)

Let's fill this out with some numbers. P(A), the probability of having the disease, is 0.01. P(B|A), the probability of a positive test result given that you have the disease, is 0.95. That gives us:

P(A|B) = ( 0.95 * 0.01 ) / P(B)

What we need to know is P(B), the overall probability of a positive test result. To figure this out, let's break it down into cases.

There are two cases to consider: the probability that you have a positive test result if you're one of the people who has the disease, plus the probability that you have a positive test result if you're not one of the people who has the disease. Here are those two cases:

1% of people actually have the disease, and 95% of those will test positive. That gives us:

0.01 * 0.95 = 0.0095

99% of people do not have the disease, and 5% of those will test positive. That gives us:

0.99 * 0.05 = 0.0495

Adding up these terms, we get an overall P(A) of:

0.0095 + 0.0495 = 0.059, or 5.9%

Now, put that term into our equation:

P(A|B) = ( 0.95 * 0.01 ) / P(B)

P(A|B) = ( 0.95 * 0.01 ) / 0.059

P(A|B) = ( 0.0095 ) / 0.059

P(A|B) = 0.161, or about 16%

It seems like mathematical sleight of hand, but it's not. A more intuitive way to explain this result is this: the test is highly accurate, but the disease is rare. Therefore, the vast majority of people who are tested won't actually have it - and the number of false positives from that group, though small compared to the size of that group, is larger than the relatively small number of people who actually have the disease and correctly test positive.

Bayesian reasoning turns up in critical thinking contexts as well. One of the best examples is in criminal trials, where both sides often make claims about the odds of a particular outcome occurring given the defendant's guilt or innocence. For example, let's assume that DNA is found at a crime scene and the police cross-check it against a database, and a match is found. The odds that the crime scene DNA would match a randomly selected DNA segment are 1 in 10 million. The police therefore arrest the person whose DNA matches and haul him into court. But the odds of the suspect's innocence are not 1 in 10 million, even though those are the odds of a match. In fact, in a country the size of America, with about 300 million people, we would expect about 30 people in the populace to match. Thus, the chances that the specific person being accused is actually the guilty party are only 1 in 30, or about 3%! (This is sometimes called the prosecutor's fallacy. See also here and here.)

The lesson to be learned here is that we should never let single cases or anecdotes guide our decisions. Given a sufficiently large pool of chance events, even very unlikely things are bound to happen on occasion. Bayes' rule gives us the tools to see those occurrences in context. On the other hand, people who pay attention only to unique and striking events, while disregarding the background they come from, are almost certain to reach incorrect conclusions.

Other posts in this series:

• How to Think Critically

There's been so much important news pouring in this month that it's hard to keep up with it. But despite the flood of information, there've been a few especially significant discoveries that I think shouldn't be overlooked. There are three that I thought deserve special notice:

• On February 13, astronomers announced the discovery of a new solar system that resembles our own more closely than any exoplanetary system that was previously known. The new system, given the unlovely designation of OGLE-2006-BLG-109, is about 5,000 light-years from Earth in the direction of the constellation Scorpius. The home star of this system is about half the mass of the Sun, and thus cooler. It's orbited by at least two planets, both gas giants, one 0.71 times the mass of Jupiter orbiting at a distance of 2.3 astronomical units (1 AU = 93 million miles), and one that's 0.27 times Jupiter's mass and orbiting at a distance of 4.6 AU - both of which now join the nearly 230 exoplanets previously known.

This marvelously specific discovery was made using a new method, called gravitational microlensing. Many exoplanets have been detected by looking for the Doppler shift in a star's light as an orbiting planet tugs it back and forth. But this method is most sensitive to large Jupiter-like planets in close-in orbits, not the best analogues of our own solar system. The new method relies on a chance alignment of stars from our vantage point, in which the light of the background star is bent and magnified in a telltale way by the gravity of the foreground star. Although not yet sensitive enough to detect terrestrial planets like our Earth, the possibility of such planets in this system hasn't been ruled out. Since this star is cooler than our Sun, there could be a habitable zone further in than the orbits of the two giant planets.

What I loved best about this discovery is that it was assisted by two amateur New Zealand astronomers, Jennie McCormick and Grant Christie, using 10-inch telescopes in backyard observatories. Even in this age of multibillion-dollar particle accelerators and space telescopes, I find it greatly inspiring that even a non-professional can still contribute to groundbreaking scientific discoveries.

• On to biology: The peerless Carl Zimmer tells us about a new transitional species in the increasingly complete fossil series that documents the evolution of whales. The 25-million-year-old Aetiocetus provides a key piece in what was a vexing puzzle: how did baleen whales evolve from toothed ancestors?

In the paper, the authors report that Aetiocetus had both teeth and baleen, based on the fossil evidence. Its skull had teeth as well as special bone troughs called nutrient foramina, which supply baleen tissue with blood in modern baleen whales and are not present in modern toothed whales.

• And another transitional fossil - this one a step in the evolution of bats. Named Onychonycteris finneyi, it comes from 52-million-year-old rocks of the Green River formation in Wyoming and is nested more deeply in the bat family tree than any bat species previously known. Although it was capable of flight, it also had several primitive characteristics not found in any living bat, including five well-formed claws on each wing, and an unusual, half-gliding/half-fluttering flying style seen in few modern bats. Based on its inner ear, it also lacked the ability to echolocate. Carl Zimmer, again, writes that it reminds him of Archaeopteryx, another electrifying specimen that gave us a glimpse into the progress of evolution over deep time.

"Saint Jnanadeva is revered for his Bhagavad Gita translation and commentary in the Maharastrian language. Among several miracles that established this 13th-century saint's reputation, the most famous involved a water buffalo. Challenged by the arrogant brahmins of Paithan that he was not qualified to recite the Vedas, Jnanadeva replied, 'Anyone can recite the Vedas.' He placed his hand upon a nearby water buffalo, which proceeded to correctly chant Vedic verses for more than an hour."

—http://www.hinduismtoday.com/archives/1995/12/15_miracles.shtml

"Thousands flocked to temples in Sri Lanka in early August 2006 after media reports that 'miracle rays' could be seen emanating from statues of the Buddha. As news of the extraordinary phenomenon spread, traffic was held up throughout the capital city of Colombo and its suburbs as large numbers of people visited temples and roadside Buddha statues.

...'Thousands vouched for having seen rays emanating from the chest of the Buddha statues and considered it a miracle,' according to an article in a Sri Lankan newspaper."

—http://www.einterface.net/gamini/buddhist.html

"I was heartbroken that my boyfriend decided to leave the relationship, so I had the Retrieve A Lover spell cast. Within a week of the spell casting, he called 'just to talk.' After some pleasant talks and catching up, he asked to see me again.

I felt he had started to turn around. I decided to date someone else just to see. He is absolutely crazy about me now and DOES see the good in me that I had hoped he would.

I am a college grad with a highly professional job. I was looking for answers. I got them.

I was so thrilled that I had the Money Spell cast a few months later. Within days I got a letter from the child support office that my child support was increasing by $172 a month!"

—http://www.calastrology.com/spelltestimonials.html

"In Kirtland, Joseph Smith made friends with a local resident, John Johnson. The Johnsons and several others visited Joseph at his home in 1831. Mrs. Johnson had been ill for years with a lame arm. It made her unable, for example, to lift her hand above her head. One of the group asked Joseph if God had given any man power to heal Mrs. Johnson. A non-member of the Church records what followed:

A few moments later, when the conversation had turned in another direction, Smith rose, and walking across the room, taking Mrs. Johnson by the hand, said in the most solemn and impressive manner, 'Woman, in the name of the Lord Jesus Christ I command thee to be whole,' and immediately left the room. The company was awe-stricken at the infinite presumption of the man, and the calm assurance with which he spoke. The sudden mental and moral shock - I know not how better to explain the well-attested fact - electrified the rheumatic arm - Mrs. Johnson at once lifted it up with ease, and on her return home the next day she was able to do her washing without difficulty or pain."

—http://www.jefflindsay.com/LDSFAQ/FQ_prophecies.shtml

"Narrated Anas:
A man came to the Prophet on a Friday while he (the Prophet) was delivering a sermon at Medina, and said, 'There is lack of rain, so please invoke your Lord to bless us with the rain.' The Prophet looked at the sky when no cloud could be detected. Then he invoked Allah for rain. Clouds started gathering together and it rained till the Medina valleys started flowing with water. It continued raining till the next Friday. Then that man (or some other man) stood up while the Prophet was delivering the Friday sermon, and said, 'We are drowned; Please invoke your Lord to withhold it (rain) from us.' The Prophet smiled and said twice or thrice, 'O Allah! Please let it rain round about us and not upon us.' The clouds started dispersing over Madinah to the right and to the left, and it rained round about Madinah and not upon Madinah. Allah showed them (the people) the miracle of His Prophet and His response to his invocation."

—http://members.tripod.com/maseeh1/advices7/id154.htm

"On May 13, 1917, a vision appeared to three shepherd children near the village of Fatima in Portugal. On a cloud that hovered above an oak tree they saw the shining figure of a woman, 'a beautiful Lady from Heaven'. The lady told the children - Lucia, 10, Francisco, 9, and Jacinta, 7 - to meet her in the same place on the 13th of each month until October.
On the first two visits only the children claimed to have actually seen the lady, but on the third and last visit, a crowd of 50,000 gathered, on a wet and dismal day, to see the last apparition. This time the shining lady, again invisible to all but the children, announced her identity: she was Our Lady of the Rosary, and she told them three 'secrets' about the future.
Then something shocking happened.
The rain suddenly stopped and the sun came out. At first it seemed to start spinning and then it began to plunge crazily toward the earth. The crowd was terrified. After a moment the sun returned to its normal position and then, twice more, repeated the same maneuver."

—http://www.mystae.com/restricted/streams/scripts/fatima.html

"These miracles were common enough in Rome, and among others this was believed, that when the Roman soldiers were sacking the city of Veii, certain of them entered the temple of Juno and spoke to the statue of the goddess, saying, 'Wilt thou come with us to Rome?' when to some it seemed that she inclined her head in assent, and to others that they heard her answer, 'Yea.'"

—Niccolo Machiavelli, Discourses on the First Ten Books of Titus Livius (1517)

Although our age is somewhat less credulous than past eras, human society is still awash in miracle claims. As the above examples show, they come from every faith and belief system, and they run the gamut: faith healings; weather miracles; snake-handling and poison-drinking; speaking in tongues; statues that move, weep, bleed, speak, eat or drink; miraculous prophecies and foretellings; psychics who claim they can view distant locations or communicate with the dead; "deliverances" from demons and evil spirits; spells and prayers to bring love, health and prosperity; "incorruptible" bodies; levitation and bilocation; divine manifestations in burned food and water damage; stigmata; multiplication of food and oil; speaking animals; and many more.

One of the greatest English-speaking philosophers of all time, David Hume, saw the fundamental problem with all these miraculous stories in his 1748 book An Enquiry Concerning Human Understanding:

To make this the better understood, let us consider, that, in matters of religion, whatever is different is contrary; and that it is impossible the religions of ancient Rome, of Turkey, of Siam, and of China should, all of them, be established on any solid foundation. Every miracle, therefore, pretended to have been wrought in any of these religions (and all of them abound in miracles), as its direct scope is to establish the particular system to which it is attributed; so has it the same force, though more indirectly, to overthrow every other system. In destroying a rival system, it likewise destroys the credit of those miracles, on which that system was established; so that all the prodigies of different religions are to be regarded as contrary facts, and the evidences of these prodigies, whether weak or strong, as opposite to each other.

...This argument may appear over subtile and refined; but is not in reality different from the reasoning of a judge, who supposes, that the credit of two witnesses, maintaining a crime against any one, is destroyed by the testimony of two others, who affirm him to have been two hundred leagues distant, at the same instant when the crime is said to have been committed.

In other words, Hume says, the conflicting miracle claims of various religions cancel each other out. These religions cannot all be true, since they make incompatible theological claims. (I note for completeness' sake that they can all be false.) We can safely assume that, if a religion is false, any miracle claims advanced in its name are exaggerations or frauds. It follows that when considering whether any particular miracle claim is true, we must consider all the miracle claims of all other religions to count as evidence to the contrary. And since there are so many of these, no matter which religion's miracle claims you're considering, the vast number of miracle claims from other religions which stand in opposition to it make the claim under consideration very probably false. It's as if there was a vast crowd of people, and whenever any one person stands to assert a claim, the entire rest of the crowd shouts out to contradict him.

Although it's useful to debunk particular miracle anecdotes - and I have nothing but admiration for the dedicated skeptics who go out to investigate every new wild-goose chase - this argument shows why we don't need to. Seven hundred years later, no one can really know for sure whether a water buffalo spoke on one occasion in the 13th century. But the burden of proof is not on the doubter to disprove. The burden of proof lies on the person making the claim, and no apologist for any religion can offer any evidence for their miracles that is superior to the evidence offered by any other. Thus, these stories offer no grounds for making a decision among all the faiths that promote them. If any miracle could be repeated, tested, under reliable and controlled conditions by independent observers, that would be something. But, so far, no religion has come anywhere close to meeting this high burden of proof.

The sole argument a theist could offer to dispute any of this, which I have no doubt will be offered by some, is for them to say that their miracles are from God, while the "miracles" of other religions are false signs performed by demons to mislead the unwary. But since any member of any religion can use that argument in exactly the same way, it is no help in deciding among them. It may soothe the troubled minds of the faithful, but it cannot have any persuasive force to anyone who is not already committed to one belief.

"Contraception is wrong because it's a deliberate violation of the design God built into the human race, often referred to as 'natural law.' The natural law purpose of sex is procreation.

...sexual pleasure within marriage becomes unnatural, and even harmful to the spouses, when it is used in a way that deliberately excludes the basic purpose of sex, which is procreation."

—http://www.catholic.com/library/Birth_Control.asp

Among Christian religions, it is a common teaching that the "natural" purpose of sex is for the creation of children, and that any other reason for sex is sinful and a subversion of God's law. This belief underlies a great deal of Christian attitudes toward sex, including the religious right's condemnation of homosexuality and extramarital sex and the Roman Catholic church's opposition to birth control.

However, while the overtly theocratic manifestations of this belief - denying civil rights to gay couples, denying emergency contraception to rape victims, attempting to ban pornography, refusing to teach young adults accurate information about sex, opposing the development of vaccines for STDs - have been attacked, and rightfully so, as far as I am aware the belief itself has rarely been challenged. That is unfortunate, because as in many other things, this is an area where the religious right stands on very shaky ground. This post will accordingly examine the facts, or lack thereof, supporting this belief.

First of all, it would seem that if the purpose of sex - the reason for sex's existence - is procreation, then all or most acts of sex should result in pregnancy. However, this is not the case among human beings. Consider what anthropologist Jared Diamond has to say in his book The Third Chimpanzee:

...even young newlyweds who omit contraception and make love at maximum frequency have only a 28 percent probability of conception per menstrual cycle. Animal breeders would be in despair if a prize cow had such low fertility, but in fact they can schedule a single artificial insemination so that the cow has a 75 percent chance of being fertilized! (p.77)

As Diamond points out, human beings are far less fertile than most animal species. And, please note, the numbers Diamond quotes are for young newlyweds. Human fertility declines steeply as we age, especially in women but also in men. Female fertility peaks between the ages of 20 and 24, begins to decline as early as the late 20s, and drops off more sharply during the 30s. By age 45, the vast majority of women are infertile (1, 2). Even if an older woman does become pregnant, her chance of miscarriage remains substantially higher than a younger woman's.

The Bible itself says that the human lifespan is between seventy and eighty years (Psalms 90:10), and given the advances in lifespan brought about by improved nutrition and modern medicine, we can safely use the higher estimate. We should then ask why, if sex is intended for procreation, it is all but impossible to use it for that purpose for about half of our natural lives. Even during the biologically brief window of maximum fertility, our rate of conception is significantly lower than that of most other animals. If sex's only or primary purpose is procreation, then it would seem to be a badly designed mechanism indeed, considering how inefficient it is for that purpose.

There is yet another biological argument that suggests that the primary purpose of sex is not procreation. In our species, females do not experience estrus - that is to say, human women do not go into heat. Virtually every other species of mammal does, and in many of those species, the onset of estrus is marked by conspicuous physical changes that advertise the female's sexual availability. For example, female chimpanzees' genitals become swollen and bright pink when they are ovulating, a sign that is obvious at a glance.

By contrast, ovulation in humans is not just not advertised, it is concealed: there are no external physical or behavioral signs that reliably indicate when a woman is capable of becoming pregnant. In addition, the length of the female menstrual cycle exhibits much more variation than cycles of estrus in other mammals, making accurate prediction difficult. (Ironically, although the rhythm method is unreliable for humans, it would work great for gorillas.) These facts, as Jared Diamond points out, ensure that most human sex acts will take place at the wrong time for fertilization. Again: if the religious right is correct and sex was designed by God primarily for procreation, why would God make it so difficult to use it for that purpose? Why would he design human beings so that we must have sex many times to stand a good chance of initiating a pregnancy?

These difficulties persist as long as one clings to the view that the only reason for sex is procreation. But if we discard that assumption, the matter comes into clear focus. An alternative explanation that accounts for the facts much better is that sex has two primary purposes: for procreation and also for pair bonding. And while pair bonding strengthens the family structure needed to raise healthy children, that is not its only purpose. In nature, it can also be used as a stress reliever, to strengthen group cohesion, as social currency, and simply for pleasure. Even homosexual sex exists in nature. Are animals violating "natural law" when they use sex for these purposes?

The concealed ovulation of females, and the constant receptivity of both genders, not just allows but encourages human beings to have sex more often than is strictly necessary for procreation. One might say that we are designed this way. If we abide by the religious right's simplistic arguments about what is natural or what we are meant to do, we are not just guided but compelled to the conclusions drawn in this essay.

However, we, unlike other animals, are not rigidly bound by the dictates of evolution and instinct. We are not required to abide by what is "natural". (If the religious right were consistent, they would also oppose eyeglasses and surgery for appendicitis - and priestly celibacy! - since those things are just as "unnatural" as condoms or birth control pills.) The purpose of sex is whatever we decide it is, and so long as we do not use it in ways that harm others or infringe on their equal right of self-determination, that decision is our right to freely make.

In all of human history, the invention of vaccination should be classed as one of our greatest medical triumphs. This innovation has saved millions of lives and prevented untold suffering and misery; it has brought many once-epidemic diseases under control, and eradicated others altogether. Tragically, our era has seen a dangerous new strain of pseudoscience emerge, one that threatens all of these gains.

The theory behind vaccines is conceptually simple. Human beings possess an exquisitely evolved immune system with a remarkable ability to learn from experience. For many diseases, once we've had them, we develop antibodies that "recognize" the particular pathogen that causes it, giving us lifelong protection against ever catching the same disease again. The innovation was to realize that we could administer killed or weakened germs - not enough to make the recipient sick, but sufficient to trigger the immune system and stimulate it to develop antibodies, so we can gain the immunity without ever having had the disease. In modern times, this technique has been refined by introducing not whole germs, but characteristic molecules that appear in a bacterium's cell membrane or a virus' protein coat. Done properly, this is sufficient to trigger the creation of antibodies.

For decades, the benefit of vaccines was unquestioned. But in the last few years, a vehement anti-vaccination movement has erupted. Hysterical, paranoid rhetoric about how doctors and pharmaceutical companies are "poisoning children" for the sake of profit are the stock in trade of this movement, which makes up in shrillness what it lacks in scientific support.

The anti-vaccine movement got its start in 1998, when a British researcher named Andrew Wakefield published a paper in the Lancet. This paper suggested that there was a link between childhood vaccination and autism, claiming that twelve (!) children who had received the measles-mumps-rubella (MMR) vaccine showed developmental regression soon thereafter. (Ten of Wakefield's twelve co-authors have subsequently retracted this interpretation, and it's been reported that Wakefield himself was being paid by trial lawyers seeking to file a lawsuit against vaccine manufacturers. This conflict of interest had not been previously disclosed, and the Lancet's editor has said he would not have accepted the paper if he had known about it.)

Despite the collapse of its scientific claims, Wakefield's paper caused a firestorm. Vaccination rates in the UK showed a significant drop soon afterward. Soon, the antivaccinationists had even identified a supposed causative agent: thimerosal, a preservative that was used in MMR and some other vaccines. The molecular structure of thimerosal contains an atom of mercury, and it was this that antivaccinationists labeled the culprit. Some went so far as to label autism a kind of mercury poisoning - an obvious falsehood for anyone who knows the symptoms of the two conditions.

In response to public fear, scientific bodies such as the CDC asked vaccine manufacturers to remove thimerosal from their products. Although this was an understandable effort to reassure people who were worried, it only added fuel to the fire. Leading antivaccinationists boldly predicted that, as thimerosal was phased out, we would see a dramatic drop in autism rates.

This did not happen. Even after thimerosal was completely removed from vaccines, autism rates continued to rise, confounding the antivaccinationists' predictions. (This is probably due to better screening and a widening of the diagnostic criteria, rather than a real increase.) In addition, numerous large, well-run studies have failed to find any causal connection between vaccination and autism.

An evidence-based movement would have dwindled away by now, but the antivaccination movement is not based on evidence. It is a pseudoscientific movement based on irrational fear, on obstinate mistrust of the medical establishment, and on the cultish sense of us-vs.-them which the movement's leaders have taken care to cultivate. The evidence weighing against thimerosal as a cause of autism has grown so overwhelming that even some antivaccinationists can no longer ignore it, but rather than change their position, many of them have simply shifted the cause of concern to conveniently undefined "toxins" (a common, meaningless buzzword of quack-medicine communities), and continue to rail against the medical establishment with equal fervor.

In some respects, vaccines are a victim of their own success: the terrible diseases they were invented to combat have been so effectively defeated that people have forgotten just how bad they were, and so they no longer fear the consequences of not vaccinating. But few of those diseases have been completely wiped out. Instead, they linger on the margins... and when a significant number of people in a community refuse vaccination, they can come back with a vengeance. In one community in Colorado, whooping cough has reemerged, with sometimes fatal results:

In 2000 it killed seventeen people in the United States, including two Colorado babies, both of whom were taken to the hospital too late. "It was very sad," Tina Albertson, a pediatric resident who cared for one of the infants, told me. "She was a six-week-old girl with a sister and a brother, four and six. The family had chosen not to immunize, and the week she was born, her siblings both had whooping cough. When they're real little, the babies don't whoop—they just stop breathing. This little girl was septic by the time they got her here."

And see also:

"It is a frightening illness to see the paroxysms of coughing, especially in very young children," Clark said. "They can cough uncontrollably and turn blue and not be able to get a breath. And it's all so concerning because it is so exquisitely transmissible."

Worst of all, parents who choose not to vaccinate are putting not just their own families but other people at risk as well. Few vaccines are 100% effective; instead, vaccination as a public health strategy relies on "herd immunity", the idea that an epidemic can never catch hold in a population of resistant individuals. But even a small number of unvaccinated people can serve as reservoirs of disease, providing a repeated source of exposure and increasing the chances that even people who are vaccinated will get sick. This form of pseudoscience is a particularly vivid illustration of the dangers of credulity.

Other posts in this series:

• Popular Delusions