Scientific truths are always provisional at some level. We once believed that the continents were fixed on the surface of Earth; now we know they move. We thought the universe was static; now we know it is expanding. We thought margarine was healthier than butter and that hormone-replacement therapy was the right treatment for vast numbers of postmenopausal women; now we know better.

But while scientists do not know everything, there is plenty they do know. Especially within this political climate, it is dispiriting to see how many people—including pundits—bizarrely reject some of the most basic, evidence-based truths that underlie modern science.

We ordinarily report on the latest advances in scientific and technological research, but we thought it appropriate to take a step back and discuss some of science's firmly established facts. There is essentially no debate among legitimate scientists about these truths, which are based on verifiable evidence, which have been accepted for decades and which have only become more strongly established as new evidence continues to accumulate.

Psychological research has shown that being confronted with that mounting evidence can actually harden the positions of the truth deniers, so we do not pretend that the essays that follow will fix the problem. Nevertheless, we feel it is our duty to point out that some things actually are true, even in the constantly growing and evolving world of science. —The Editors

Evolution is the only reasonable explanation for the diversity of life on earth

On January 14, 1844, Charles Darwin wrote a letter to his friend Joseph Hooker, recalling his voyage around the world on the HMS Beagle. After five years at sea and seven years at home thinking about the origin of species, Darwin came to this conclusion: “At last gleams of light have come, & I am almost convinced (quite contrary to opinion I started with) that species are not (it is like confessing a murder) immutable.”

Like confessing a murder. Dramatic words. But it doesn't take a rocket scientist—or an English naturalist—to understand why a theory on the origin of species by means of natural selection would be so controversial. If new species are created naturally—not supernaturally—what place, then, for God? No wonder that more than a century and a half later people of some religious faiths still find the theory so terribly threatening. But in those intervening years scientists have found so much evidence in support of the theory that it would be truly astonishing if it turned out not to be true—as shocking as if the germ theory of disease fell apart or if astrophysicists were forced to abandon the big bang model of the universe. Why? Because of a convergence of evidence from many lines of inquiry.

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For example: Comparing data from research in population genetics, geography, ecology, archaeology, physical anthropology and linguistics, scientists discovered that Australian Aborigines are genetically more closely related to South Asians than they are to African blacks—which makes sense from an evolutionary perspective because the migration pattern of humans out of Africa led them to Asia and then to Australia.

The consistency of dating techniques also gives us confidence that the theory is true. Uranium-lead, rubidium-strontium and potassium-argon dating, for example, are all reasonably consistent in their determination of the age of rocks and fossils. The ages are given in estimates, but the margins of error are in the range of 1 percent. It is not as if one scientist finds that a fossil hominin is 1.2 million years old while another one finds it is 10,000 years old.

Not only are the dates consistent, but the fossils also show intermediate stages—something antievolutionists still insist don't exist. There are now at least six intermediate fossil stages in the evolution of whales, for instance, and more than a dozen fossil hominins, several of which must have been intermediate with humans since the hominins branched off from chimpanzees six million years ago. And geologic strata consistently reveal the same sequence of fossils. Trilobites and mammals are separated by many millions of years, so finding a fossil horse in the same geologic stratum as a trilobite—or even more drastically, a fossil hominin in the same stratum as a dinosaur—would prove problematic for the theory of evolution, but that has never happened.

Finally, vestigial structures are signs of evolutionary history. The Cretaceous snake Pachyrhachis problematicus had small hind limbs, which are gone in most of today's snakes. Modern whales retain a tiny pelvis for hind legs that existed in their land-mammal ancestors. Likewise, flightless birds have wings. And of course, humans are replete with useless vestigial structures—a distinctive sign of our evolutionary ancestry—such as wisdom teeth, male nipples, body hair, the appendix and the coccyx.

As the great geneticist and evolutionary theorist Theodosius Dobzhansky famously noted, “Nothing in biology makes sense except in the light of evolution.” —Michael Shermer

Homeopathy has no basis in science

Homeopathy is a system of medicine that purports to treat disease with minute doses of substances that in a healthy person would produce symptoms of that disease. It is based on the unscientific thinking of a single misguided individual, a German doctor named Samuel Hahnemann, who invented it in the early 1800s.

Homeopathy not only doesn't work; it couldn't possibly work. It is inconsistent with our basic knowledge of physics, chemistry and biology. Oliver Wendell Holmes thoroughly debunked it in 1842 with his essay “Homeopathy and Its Kindred Delusions.” He would have been appalled to think anyone could still believe it in 2016.

Few users of homeopathy have bothered to inform themselves about what they are taking or the wacky ideas behind it. The simplest way to explain homeopathic theory is with this example: If coffee keeps you awake, dilute coffee will put you to sleep—the more dilute, the stronger the effect. If you dilute it until there isn't a single molecule of coffee left, it will be even stronger. (The water will somehow remember the coffee that is no longer there.) If you drip the coffee-free water onto a sugar pill and let it evaporate, the memory of coffee will be transferred to the sugar pill, and the pill will relieve insomnia.

If any of that makes sense to you, you should be worried.

You wouldn't think anyone would buy a medicine that contained no active ingredient, but they do. A product called Oscillococcinum is sold in most American pharmacies, bringing in an estimated $15 million a year from customers hoping to relieve the symptoms of flu and colds. The name is that of the oscillating bacteria that a French physician, Joseph Roy, imagined he could see in the blood of flu victims and in duck liver; no one else ever saw them. The box says the active ingredient is Anas barbariae 200 CK HPUS. That means Muscovy duck (the heart and liver), and it means they diluted it 1:100 and repeated that process 200 times, “succussing” it after each dilution (it is shaken, not stirred). Any chemistry student can use Avogadro's number to calculate that by the 13th dilution, there is only a 50–50 chance that a single molecule of duck remains, and by the 200th dilution the duck is history. All that remains is the quack.

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Homeopaths' prescribing methods are unbelievably silly. They ask a laundry list of irrelevant questions (What color are your eyes? What foods do you dislike? What are you afraid of?). They consult two books. The first is a Repertory listing remedies for every possible symptom—for example, clairvoyance (yes, it considers this a symptom), dental caries and “tearful” (sic). The second is a Materia Medica listing the symptoms associated with each remedy (“dreams of robbers” are linked to table salt!). Yes, dilute table salt and pretty much anything imaginable can be a remedy. Some of my favorites: Berlin wall, eclipsed moonlight, dog's earwax and the south pole of a magnet. It's absurd, but an estimated five million adults and one million children use homeopathic remedies every year in the U.S., mostly self-prescribed and purchased in a pharmacy.

Even though there are published studies claiming that homeopathy works, you can find a study to support almost anything, and rigorous scientific reviews of the entire body of research have consistently concluded that it works no better than placebos. As Edzard Ernst, emeritus professor of complementary medicine at the University of Exeter in England, and author Simon Singh have written, “The evidence points towards a bogus industry that offers patients nothing more than a fantasy.”

The FDA allows the sale of homeopathic remedies under a “grandfather” clause exempting them from the requirement to demonstrate effectiveness, but it is considering changes in regulation. I wish they would require a label stating, “Contains no active ingredient. For entertainment purposes only.” So far people have used homeopathy instead of effective drugs, vaccines and malaria prophylaxis with disastrous results. People have died.

Homeopathy was bunk in 1842, and it remains bunk today. By now we ought to know better. —Harriet Hall

Climate change conspiracy theories are ludicrous

I'm always baffled that some people have convinced themselves that the scientific consensus underpinning anthropogenic global warming is a vast conspiracy to destroy the American way of life, foist socialism on the unsuspecting masses, or ... insert your favorite gripe here.

If it is a conspiracy, it is a truly remarkable one, spanning nearly two centuries and the scientific communities of dozens of nations. The foundations of our understanding of planetary temperature begin with the work in the 1820s of French physicist Joseph Fourier, who established that a planet's temperature is determined by the balance between energy received from the sun and infrared radiation emitted back into space. Quantification of Fourier's basic idea depended on the development of blackbody radiation theory by Austrian Ludwig Boltzmann in the mid-1800s and his German contemporary Gustav Kirchhoff. Irish-born physicist John Tyndall brought carbon dioxide into the picture in the late 19th century by showing that it traps infrared radiation, and Swedish chemist Svante Arrhenius put it all together shortly thereafter.

There were many later developments in the 20th century, culminating in a quite complete theory incorporating both carbon dioxide and water vapor feedback, which Syukuro Manabe developed while working at NOAA's Geophysical Fluid Dynamics Laboratory in the 1960s and 1970s. We have learned plenty since then, but Manabe basically nailed it. Our understanding of the connection between greenhouse gases and global warming rests on the same principles that underlie heat-seeking missiles, weather satellites and infrared remote controls. It would take quite a conspiracy to fake all that.

It would take an even greater conspiracy to fake the changes in Earth's climate that theory predicts and scientists have observed, including higher global average temperatures, rising sea levels, dwindling ice in the Arctic and Antarctic, melting glaciers, increases in the intensity and duration of heat waves, and more. The cabal would also have to fake all the data from past climates that tell us there is no magic mechanism (clouds or otherwise) that will save us from the well-established warming effects of carbon dioxide acting in concert with water vapor. It would have to fake the observations that tell us that subsurface ocean waters are warming—evidence that the energy that is heating the planet's surface is not coming from the oceans. (Energy is conserved, so if the oceans were causing surface warming, then they would be cooling down in response. Conservation is not just a personal virtue—it's the law!) Likewise the carbon isotope and carbon budget data that prove that the carbon dioxide accumulating in the atmosphere really does come from deforestation and burning fossil fuels. It would have to fake the observed conjunction of stratospheric cooling with tropospheric warming, which is characteristic of the influence of carbon dioxide and other long-lived greenhouse gases on the atmosphere.

And so on and so forth. It adds up to an awful lot of stuff to fake and makes faking the moon landing look like a piece of cake.

Science rewards those who overturn previous dogma (think quantum theory versus classical mechanics), so the fact that the basic theory of anthropogenic global warming has weathered all challenges since appearing in its modern form in the 1960s is saying a lot. Global warming is a problem, and we caused it. That's still true even if Donald Trump disagrees. Arguing about the basic existence of the problem has no place in a sane discourse. —Ray Pierrehumbert

Vaccines do not cause autism

It has been almost 20 years since a paper published in the Lancet gave birth to the notion that vaccines caused autism. Since then, more than two dozen studies have refuted the claim, and the original paper has been retracted.

For the most part, the money and time devoted to studying the vaccine-autism hypothesis have been worth it. First, media outlets no longer carry this story under the false mantra of balance, telling two sides when only one is supported by the science. Now the story is one of a disproved claim proposed by a discredited doctor. Second, most parents no longer believe that vaccines cause autism. A recent study showed that 85 percent of parents of children with autism do not believe that vaccines were the cause.

Unfortunately, despite the mountain of evidence refuting the association, a small group of parents still believe that vaccines might cause autism. Their failure to vaccinate their children not only endangers the children but also weakens the “herd immunity” that keeps disease outbreaks contained. There are several plausible reasons why they feel this way.

One possibility is that the cause or causes of autism remain unknown—the same situation that applied to diabetes in the 1800s, when no one knew what caused it or how to treat it. At the time, people proposed a variety of crazy causes and heroic cures. Then, in 1921, Frederick Banting and Charles Best discovered insulin, and all these false beliefs melted away. Until a clear cause and cure for autism emerge, the vaccine hypothesis will be hard to put completely to rest.

Another possibility is that the notion that vaccines cause autism is comforting—certainly far more comforting than studies that have shown a genetic basis. If autism is caused by events occurring outside the womb, then parents can exercise some form of control. If the disorder is genetic, there is no control.

And everyone loves a bogeyman. It is nice to be able to point a finger at an evil force causing autism, especially if it is big pharma or big government. Conspiracy theorists argue that the only reason studies have shown that vaccines do not cause autism is that a vast international conspiracy is hiding the truth. Although only a small group of parents hold this belief, their voices are disproportionally represented on the Internet.

Finally, parents of children with autism often perceive them as developing normally up to about 12 months of age. Then, after receiving a series of vaccines, the child misses speech, language, behavior and communication milestones typically seen in the second year of life. In fact, several studies examining videotapes taken in the first year of life show that these children were not developing normally. But from the parents' perspective, they were.

The most encouraging aspect of the vaccine-autism controversy has been the emergence of academics, clinicians, public health officials and parents who have taken to the Internet, the airways and the print media to represent the science that has exonerated vaccines. As a consequence, the tide has turned. We now hear the voices of parents who are angry that other parents, by choosing not to vaccinate, have put all children at risk.

This societal outcry in favor of vaccines was made all the more immediate by the 2015 measles outbreak, which began at the Disney theme park in California and spread to 189 people, mostly children, in 24 states and the District of Columbia. Sadly, nothing educates better than the virus. Invariably, it is the children who suffer our ignorance. —Paul Offit

No credible evidence of alien visitations exists

Millions of people in the U.S. claim they have been abducted by aliens, according to a 2013 story in the Washington Post. That's an impressive tally for the aliens. And yet the government's response has been tepid. That should tell you something: either the Feds think it's not happening, or they're part of the problem.

Many people believe the latter. They say that the government knows the aliens are here but keeps the evidence under wraps at Area 51 or some other top-secret venue.

But hold on.

Unless extraterrestrials prefer Americans (and exceptionalism aside, why should they?), then the rate of abduction worldwide shouldn't be terribly different from what it is here. Assuming an aliens-without-borders effort, tens of millions of folks around the world have been grabbed by the grays. I think the United Nations would notice. I think you'd notice.

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Abductions, of course, are only one component of the so-called UFO phenomenon. The majority of the evidence is composed of sightings—eyewitness accounts, photographs and videos. Most of these can be explained as aircraft, rockets, balloons, bright planets or, occasionally, hoaxes. Some remain unexplained—but that only means they are unexplained, not that they are flying saucers, no matter how convinced the people who report them might be. There remains no scientifically validated evidence that extraterrestrials have been here, either recently or in the distant past. The pyramids, the Nazca lines in Peru and all the other artifacts that have been ascribed to ancient astronauts can be straightforwardly explained by human activity.

In fact, few scientists or science museum curators feel that the claim we are being visited is even plausible. Even aside from the formidable technical challenges of interstellar travel, ask yourself this: Why are they here now? Homo sapiens has been broadcasting its presence to the universe only since the advent of television and radar. Unless the extraterrestrials come from a very close star system, there has not been adequate time for them to learn of our existence and fly to Earth.

Even if they could get here at the speed of light (which they could not), they would have to live within 35 or so light-years of us—and there are not all that many close stars. Besides, high-speed space travel requires an enormous amount of energy. Would you pay a gargantuan utility bill just for a little “catch and release” sportfishing for hominins?

Nevertheless, for decades polls have shown that roughly one third of the populace believes our world is host to cosmic visitors. If despite the lack of good evidence, you insist on believing this is true, you also have to admit they are the best guests you could ever have. They don't kill us, they don't foment unrest, they don't steal the silverware. The Roswell incident was nearly 70 years ago. If aliens have been here since, they deserve good conduct medals. —Seth Shostak

10 More Irrefutable Facts

MONSTERS, INC.—Bigfoot, the Loch Ness monster and similar creatures do not exist. The idea that large, unknown animals roam the woods of the Pacific Northwest, glide through chilly Scottish waters and hike the Himalayas is eerily appealing, but the evidence is basically zero.

GMOs ARE NOT SCARY—“Frankenfoods” sound like a terrifying concept, but despite extensive testing, genetically modified organisms have never been shown to be dangerous.

100% BS—No, we do not use only 10 percent of our brainpower. Nobody knows where this “fact” even came from, but it's nonsense.

THIS IDEA IS ALL WET—You do not need to drink eight glasses of water a day. You do have to replace fluids lost to urine and perspiration, but some comes from food, and there's no set amount.

EXPENSIVE URINE—Unless you have a deficiency or no access to healthy food or a balanced diet, vitamin supplements are pretty much a waste of time and money.

DON'T FALL OFF THE EDGE—No, just kidding. Earth is not flat. Christopher Columbus knew it when he set sail. You know it, too. Or most of you do, anyway.

NO FREE LUNCH—Free energy and perpetual motion sound great. But thermodynamics says no way, and that's the law.

CRIME SEEN—Or rather, not seen. Criminal activity does not increase during the full moon. It can seem that way, even to police officers, because you notice things that confirm your expectations. But despite a handful of suspicious-looking studies, most research says the idea is lunacy.

RATATOUILLE—Treating cancer in rodents is not the same as doing so in humans. Animal tests have led to many new treatments. But if you hear that a cure based on rodents is on the way, you should smell a rat.