Science

Michael Lugo pointed out this article explaining why the shape of the moon’s orbit around the sun is not what you might expect.

60-Second Science has a story about a bizarre form of animal defense. There are caterpillars that vomit on attackers. And they don’t spew corrosive chemicals as animals sometimes do. They spew surfactants (think soap). Audio

The duck-billed platypus is the most recent species to have its genome sequenced. These odd animals are even more strange at the DNA level. Some features of their DNA are avian, some are reptilian, and of course some are mammalian. See the Science Daily article for more details.

Yesterday’s Science at NASA podcast had an entertaining story about duct tape and Apollo 17. (Transcript, audio)

The lunar rover lost a fender and they taped it back on with duct tape. That worked for a while, then they had to make a new fender with laminated maps and duct tape.

Why is a fender such a big deal? Without a fender, the astronauts would get dirty. So why is that a big deal?

1. Dirt is dark, and dark absorbs sun light. A dirty astronaut may become a fried astronaut.
2. Dirt scratches visors, making it hard to see.
3. Dirt gets in parts like hinges and breaks them.

According to a Science Magazine story, it looks like humans have been in North America one thousand years longer than previously believed. New DNA evidence suggests people were in North America by 12,000 B.C. The study also suggests that the first Native Americans may have arrived via the Pacific Coast rather than migrating across the land bridge that once connected Asia and North America.

Read the article or listed to the podcast.

According to the latest Scientific American podcast, there is no scientific evidence to back up the common belief that everyone should drink eight glasses of water per day. Nor is there scientific evidence to back up many of the claimed benefits of increased water consumption: improved skin, better regulated appetite, etc.

However, the podcast equates “no scientific evidence” with “not true.” The title of the podcast is The Mythical Daily Water Requirement. “Mythical” means “false.” (There are more nuanced uses of the word “myth,” but I don’t think they are relevant here.)

It has been known for some time that the eight-glass-a-day recommendation is not well substantiated by experiments. That’s not to say increased water consumption isn’t beneficial. After all, there have not been any randomized trials to prove that parachutes improve your chances of survival when jumping from an airplane either.

Randomized trials are not the only way to learn about the world, and are not as effective as commonly believed. Most published research findings are false. Randomized trials are a tool for exploring reality, sometimes the best tool for a particular task, but not the only tool.

It’s plausible that drinking eight glasses of water per day is beneficial, or at least harmless, based on anecdotal evidence. Certainly drinking too little water is fatal (though there have been no randomized trials to confirm this!) and so it is reasonable to presume there is some curve showing increased benefit with increased water intake, up to a point. The curve would go back down at some point, as it is possible to drink too much water. It would be interesting to see randomized studies to explore where the curve flattens out, exploring consumption levels safely between the harmful extremes.

It is widely assumed that parachute use improves your chances of surviving a leap from an airplane. However, a meta analysis suggests this practice is not adequately supported by controlled experiments. See the article Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomized controlled trials by Gordon C S Smith and Jill P Pell. The authors summarize their conclusions in the abstract.

As with many interventions intended to prevent ill health, the effectiveness of parachutes has not been subjected to rigorous evaluation by using randomised controlled trials. Advocates of evidence based medicine have criticised the adoption of interventions evaluated by using only observational data. We think that everyone might benefit if the most radical protagonists of evidence based medicine organised and participated in a double blind, randomised, placebo controlled, crossover trial of the parachute.

In 1601, an English sea captain did a controlled experiment to test whether lemon juice could prevent scurvy.  He had four ships, three control and one experimental.  The experimental group got three teaspoons of lemon juice a day while the control group received none. No one in the experimental group developed scurvy while 110 out of 278 in the control group died of scurvy. Nevertheless, citrus juice was not fully adopted to prevent scurvy until 1865.

Overwhelming evidence of superiority is not sufficient to drive innovation.

Source: Diffusion of Innovations

The March 6 Nature podcast has a story about the Large Hadron Collider. The LHC is expected to gather 15 petabytes (15,000,000 gigabytes) of data. One of the people interviewed said that 15 petabytes of data would require a stack of DVDs the height of Mount Blanc.

You probabily have someone else’s cells growing inside you.

In a phenomena known as microchimerism, mothers pass some of their cells onto their children, and vice versa, during pregnancy. That’s not too surprising in itself. What is more surprising is that these cells can reproduce for decades. It’s not uncommon to find female cells in a grown man, or male cells in a woman who gave birth to a son. 

See “Your Cells Are My Cells” in Scientific American, February 2008.

The 60-Second Science podcast from February 27, 2008 tells of plans for NASA and MIT to build a giant radio telescope on the dark side of the moon. (The “dark” side is really the “far” side, the side that always faces away from Earth. It gets just as much sunlight as the side we’re familiar with.) This side of the moon is shielded from radio noise from Earth, and so a radio telescope there could detect radio signals further back in time than is possible here. The plan is to use robots to assemble radio antennas over two square kilometers.

The February 20^th Science at NASA podcast gives a brief overview of the upcoming lunar exploration efforts by China, Japan, India, Russia, and the United States. Within four years there could be nine satellites orbiting the moon.

The podcast site has a transcript as well as the audio file.

My previous two posts have been about false research conclusions and false positives in medical tests. The two are closely related.

With medical testing, the prevalence of the disease in the population at large matters greatly when deciding how much credibility to give a positive test result. Clinical studies are similar. The proportion of potential genuine improvements in the class of treatments being tested is an important factor in deciding how credible a conclusion is.

In medical tests and clinical studies,  we’re often given the opposite of what we want to know. We’re given the probability of the evidence given the conclusion, but we want to know the probability of the conclusion given the evidence. These two probabilities may be similar, or they may be very different.

The analogy between false positives in medical testing and false positives in clinical studies is helpful, because the former is easier to understand that the latter. But the problem of false conclusions in clinical studies is more complicated. For one thing, there is no publication bias in medical tests: patients get the results, whether positive or negative. In research, negative results are usually not published.

Until quite recently, astronomers thought that comets formed in the outer reaches of the solar system and then were drawn into highly elliptical orbits that pass near the sun. But samples collected from comet Wild 2 look more like they came from the inner solar system like asteroids. Maybe the outer solar system is more like the inner solar system, or maybe comets didn’t form where we thought they did.

For more details, listen to yesterday’s 60-Second Science podcast or read the Science Magazine article the podcast is based on.