Off the top of your head, what is the world's population?
Did you answer 4.5 billion? 5 billion? 6 billion? more?
The correct answer, according to the UN's latest calculation, is just over 7.5 billion. If you guessed wrong, you're probably in good company, because the wrong answers can predict when you went to high school.
Think there are 6 billion people in the world? You probably went to high school in the late 1990s. 4.5 billion? You probably graduated in the 1980s. 7 billion You likely graduated within the last couple of years.
Why do our guesses about the world's population take us back to our more regrettable hairstyle choices? To answer that, we have to think about facts. There are fixed facts (birthdays, state capitals, building heights) and rapidly changing facts (like the temperature). Samuel Arbesman, writing seven years and 700 million fewer people ago, describes a third kind of fact that changes slowly enough that we often don't realize it, but fast enough for us to be wrong about it within our lifetimes. Arbesman calls these types of facts mesofacts.
Arbesman's best examples are about things we tend to learn when we are very young. Dinosaurs aren't the cold-blooded creatures many of us learned them to be, but warm-blooded, wildly-colored even feathered animals. We all know there are 9--oops, 8--planets (sorry, Pluto), but many of us grossly underestimate how many others there are outside of it: 400 when Arbesman introduced mesofacts. NASA's Kepler telescope, which became operational at about the same time Arbesman wrote that there were 400 known planets, ended up locating over 1,000 more. Given that the Milky Way contains about 100 billion stars, of which our sun is just one, this mesofact is likely to change a great deal more during our lifetimes.
When you start looking for mesofacts, you'll notice them everywhere. For example, if I ask you to name as many dinosaurs as you can, you'd probably list off the ones you know from Jurassic Park: T-Rex, Velociraptor, that tiny one that gets Newman in the face. Maybe you'd even remember Pterodactyl. If you're parent to a young child, chances are you know the names of a lot more. You're also likely to learn that Brontosaurus never existed! Turns out that what paleontologists thought was a new dinosaur was just another apatosaurus. Given its chameleonic tendencies, it's fitting that Apatosaurus means "deceptive lizard."
Mesofacts don't end with interesting trivia. Parents acknowledge mesofacts all the time without using the term. They're just labeled "things grandma gets wrong," parenting practices that were thought to be safe but now are considered unsafe or even deadly. A quick Google search will turn up dozens of articles about what to teach grandma before you let your kids sleep at her house, despite the fact that you, now an adult, are evidence that grandma seemed to manage just fine.
Of course we should tell older family members about "back to sleep" and other evolving safety practices. But given what we know about mesofacts, we should also probably be humble about our own parenting knowledge. It's likely that, a few decades from now, our adult children won't want to leave their children at our house because of all the things we don't know about parenting safely.
What am I doing to help be more attentive to mesofacts?
First, when I encounter a new study about parenting, I try to withhold skepticism. It's so easy to read a headline and immediately conclude that the contents are true or false, depending on my own previous experiences and the political/philosophical leanings of the news organization. Instead of jumping to conclusions that depend on what I want the outcome to be, I try to ask "why" and "how" questions of what I'm reading. This helps keep me more open to changing news instead of ignoring it.
Second, even when I feel I've "mastered" some aspect of parenting (like getting my three-year old to nap for five! days! in! a! row!), my sample size is just one child. There's no evidence that what I'm doing is actually what put my child to sleep, and even if I was keeping careful track of what's different about this week than last week, I could not extrapolate my results to include all other children. All parents are working with tiny sample sizes, so we should all recognize that our knowledge of parenting is tentative and incomplete.
Even as I establish this tentative mastery over day-to-day family life, I'm trying to keep myself open to new and contradictory ideas. So the third move I'm making to keep myself open to mesofacts is finding ways to say "I don't know." I find that, even if I'm doing the same science experiments with my child as we did the day before, or having the same fight about putting away laundry, there are always new things to explore. The more I say "I don't know," the more open and interesting my days are. So I'm trying to stake less claim over things that I know to be true and instead treating everything as something I don't know enough about yet.