Hi there,

This week I've got some science news that won't put you to sleep, but might help you sleep better when you take a siesta. Researchers pulled together a bunch of research about naps – specifically about what makes them good for you or bad for you, and the result is a neat perspective on the habit, along with a bit of advice about how to nap better. That's my #1 story.

Before that, a tale of 1,000 people who buried their underwear for science, a critique of online critiques, and a neat paper about something your dog's been doing to show their love to you that you probably haven't even noticed.

Before we get to those, though, one of the most interesting scientific questions I've seen in a while: What is it about the acoustics of bird calls that makes them so pleasing to the ear? Let's start there.

Here's an example of a fabulous question. I just love this: We all know that people tend to like the sounds that birds make, but which bird sounds are most pleasing to the human ear, and why?

To answer that lovely question, researchers in Germany got humans' ratings for the sounds made by 123 different bird species that occur in that country, and then looked for correlations between those sounds' acoustic characteristics and their popularity. What they found was really quite cool.

In the study, 84 adults listened to 15-second recordings of each bird, and then rated its sound on a scale from 1 (not pleasant) to 5 (very pleasant). It was like one of those TV shows where judges sit in red chairs and say mean things to people who perform for them, but less cold-hearted and disrespectful.

Anyway, the big winner among the German birds included in the study was the Eurasian Blackbird, with a score of 4.52 out of five. And if you listen to each of them, you can see why. It's not hard to understand why Paul McCartney did NOT write his song about a Barn Owl singing in the dead of night.

(Here are links so you can hear them yourself: Eurasian Blackbird, Barn Owl).

Had the researchers stopped there, the study would have been a popularity contest, and nothing more. But they didn't stop there. They ran the analysis on call structure, and this is where things get super cool. People like a bird's sound if...

• The lowest pitch of the bird call, and the bulk of the sound overall, aren’t very low-pitched.
• The bird’s call is not too loud.
  
• The complexity of the call is high (lots of different notes) – but the bird’s call stays within a narrow band of frequencies (pitches).
• The highest pitch of the bird song isn’t too high – it doesn’t hit that sweet spot at which our hearing is most sensitive, around 2.4–5.5 kHz (where babies cry, and brakes squeak).

Interestingly, whether someone was a hardcore birder or a total novice made no difference to their ratings; the only personal trait that mattered was how much someone said they generally valued birds in the first place – people who value and like birds rate their sounds as more pleasant.

Scientists in Switzerland asked 1,000 volunteers to bury cotton underwear in their gardens, farms, and lawns, then dig them up a month or two later, to see how much they'd decomposed. The idea is that the underwear's degradation should be a good index of a soil's biological activity. And involving the public helps to make those people more aware of the importance of soil health.

Private gardens devoured underwear fastest, breaking down 58% of the fabric within two months, while lawns lagged behind at just 40%. Farm fields and grasslands landed somewhere in between. Much of the difference comes down to fertilizer; home gardeners put far more nutrients into their soil than their plants can use, and microbes flourish as a result.

The citizen science angle is fun. Researchers recruited volunteers through a media blitz on Swiss TV and radio, and then mailed out activity packs. Each one containing two pairs of organic cotton underwear, a dozen teabags, and instructions for burying everything about eight centimetres deep. After one month, participants dug up the first pair of underwear along with some teabags, and after two months, they retrieved the rest. And people loved it. Of the 1,100 kits (2,200 pairs of underwear) mailed out, people returned more than 1,700 pairs of decomposed underwear and more than 7,000 teabags. That's some serious participation! Here's a link to the paper.

In general, online reviews are a good way to guess a product's overall quality. But a new commentary in the journal Nature Human Behaviour, based on two decades of research on consumer behaviour, points out three reasons those reviews might not be telling you what you think they are.

1. To mislead consumers for personal gain: If I run a restaurant, I might encourage my friends and family to write negative reviews about the restaurant across the street.
   
2. To be funny: The 5-star reviews of the wolf shirt in the image above are a classic example of this (“Upon first glance, I knew this shirt was the living incarnation of all mankind was meant to be and achieve.”). You can also find ironic one-star reviews of the Grand Canyon on travel sites, lamenting its lack of roller coasters, for example.
3. To make a political statement: Lots of people "review bombed" this summer's film The Odyssey because they were bothered by the racial/gender diversity of the cast. A similar thing happened when one of the characters on Stranger Things came out as gay in an episode. Many people panned the show in response, having never even watched the episode in question.

The authors note when reviews are influenced by these phenomena, the distribution of reviews can end up with a J-shaped pattern, with many, many reviews at one end of the spectrum, instead of a bell-shaped distribution, like you might get for actual ratings. That pattern, they offer, could be a red flag that there’s something going on besides honest reviews. But fundamentally, it’s impossible to know, and the authors warn that generative A.I. could make the problem worse by allowing convincing fake reviews to be produced at scale.

A fun new study shows that when a dog watches a video of its owner blinking, it blinks more often than if it watches a video of its owner with their eyes kept open.

Cool right? But here's something even cooler...

If those same dogs watch videos of strangers, the blinking has no influence. Blinking is like a secret handshake that only works between an owner and their dog.

One other piece of the story is that the effect was especially strong for dogs with female owners. Dogs looking at their male owners increased blink rates by around 75%, but the dogs with female owners responded with increases of 89%, on average. Although they analyzed the genders separately, they didn't analyze whether they were significantly different from one another, so the apparent gender difference might just be statistical noise. But it's clear from the data that the difference between owner and non-owner is as different as night and day.

Why dogs do this is an open question. I'd guess blinking among dogs has some meaning, and that dogs have carried that language over to the way they interact with their owners. And to think we don't even notice! I almost feel bad for not blinking more when my dog blinks!

I started this newsletter off with a good question about birds, now here's a question we thought was good, but that turns out to be bad: Is napping good for you or bad for you?

For decades, scientists have been fighting over this question. Some studies show that naps are linked with improvements in cardiovascular function. Other studies link napping to obesity, diabetes, and increased mortality risk. Which is it – good or bad?

A new commentary in the journal Sleep Health, argues that we haven't answered that question because it's fundamentally flawed. It assumes that all naps are equal. That is like asking whether food is good or bad, without specifying whether we're talking about a kale salad at lunch or a second milkshake at 3AM. For naps, they argue, context matters.

The authors pull together a bunch of research, including their own, and draw up a list of eight variables that they say need to be considered. Some of them come with suggestions (I've highlighted blue), but others are just variables that the researchers think matter, and need to be teased apart in future studies:

• Duration: How long is your nap? Studies have shown that short naps (less than 30 min) improve alertness and cognitive performance, while long naps are linked to bad cardiovascular outcomes. So try to keep your naps under 30 minutes.
  
• Timing: When do you take that nap? One study showed that people with the lowest body mass indices (BMIs) tend to nap 7h:15m after waking (give or take an hour or two), which comes out to about an hour after lunch. People who nap earlier or later than that ideal siesta time tend to have higher BMIs, with the highest BMIs associated with naps 3h after waking up – that is, napping before lunch. So take your nap an hour after lunch.
• Frequency: How many days a week do you nap? There's no clear answer in the literature yet about what is best – it may depend on the context of other factors. The researchers say this probably influences how naps affect you, they just don't know how.
• Motivation: Are you napping to relax, or because you're exhausted? If you're exhausted, your nap may be compensation for insufficient sleep or an increased need for sleep that's caused by some other factor. If you're sleeping to relax, sleep may be serving a different restorative function, or be more of a social habit. Those differences probably influence what effect napping has on your health, but it's unknown how.

• Genetics: Does napping run in your family? Twin studies suggest that genetics may account for up to 65% of the differences in habitual napping among individuals. Some people really are wired for napping, and it's assumed napping is especially helpful for them.
• Environment: Do you live somewhere hot? Siestas are more common in warm places. Is that because they're more restorative when it's hot?
• Seasonality: Are you getting enough sunlight? Are winter naps the same as summer ones?
• Circadian alignment: Do you work nights? How can naps be most helpful to people who have disrupted sleep cycles? 

The hope is that researchers in the field will read this paper, take this list to heart, and start designing experiments and studies that drill down on these variables one at a time.

Last Week's Trivial Answer

Last week's question was "The French word for bat is chauve-souris. What do those two words mean in English?" The correct answer was "Bald Mouse."

Thanks for reading! -Dan