Till Roenneberg’s “Internal Time”: Book Review, Notes + Analysis

Poor Ash’s Almanack > Book Reviews > Science > Biology

Overall Rating: ★★★★★★★ (7/7) (life-changing)

Learning Potential / Utility: ★★★★★★★ (7/7)

Readability: ★★★★★★★ (7/7)

Challenge Level: 3/5 (Intermediate) | 231 pages ex-notes (288 official)

Blurb/Description: Chronobiologist Till Roenneberg delivers a profoundly important, insightful, and witty scientific investigation of chronotypes and the circadian rhythm.

Summary: I’ve known about Peter Thiel’s favorite question – “tell me something that’s true, that almost nobody agrees with you on” – for a long time.  I never thought I had a good answer.

Till Roenneberg’s phenomenal Internal Time made me realize I did.  My answer to the Peter Thiel question in two words: chronotypes matter.  In a few more: they matter for productivity, health, and happiness on both an individual and social level.  Pushing high school start times back by a few hours, and general workplace start times by at least an hour, would be the holy grail of public policy: a “free lunch” providing substantial benefits at little to no cost.

In a brief and accessible yet insightful, engaging, and deeply scientific book, Roenneberg provides a thorough, thoughtful explanation of our “internal clock,” driving home a lot of mental models in the process ranging from schema bottlenecks to culture / status quo bias to trait adaptivity.

Highlights: Chronotypes have a particular resonance for me personally because one of the major inputs into my decision to start my own fund is that I’m a latechronotype (~7:30, per the way chronobiologists actually measure it), and chronic sleep deprivation on account of my job was causing a diverse, severe, and unbearable range of physical and emotional challenges.  The substantial majority of these resolved nearly immediately upon being able to control my sleepschedule, and the remainder resolved over time.

I’d go so far as to call sleep my secret weapon: even when I was working full-time while taking 2x the normal load of courses in grad school, I prioritizedsleep above all else, because that was the only thing that made everything else go.  While sleep is certainly not the sole component or driver of my overall health – I’m also focused on eating right, exercising, and minimizing stress – it’s fair to say that sleep is my #1 health priority, and the primary driver of both my physical health and my ability to make effective decisions.

My case is an extreme example, because most people’s circadian rhythms are somewhat more adaptable than mine (though, as Roenneberg points out with irrefutable evidence, not nearly as much as morning types claim they are.)  As such, I don’t expect all readers will get the same mileage out of it that I do, but I strongly believe that sleep (and, specifically, the chronic sleep deprivation that results across the population as a result of a maladaptive  culture heuristic carried over from previous eras that conflicts with a very different modern environment causing us to be laterchronotypes than we were historically) is a fundamental topic that deserves far more attention than it gets.

Lowlights: None, other than the fact that the science is somewhat technical at points and you may need to read slowly / read a few times to fully understand, for example, the process of entrainment.

Mental Model / ART Thinking Points: utility, emergence, disaggregationinversionculture, one to many, multicausalityfeedback, intrinsic motivation, sample sizeempathyschemabottleneck,sleepproduct vs. packagingagencycontrast biassaliencetrait adaptivity

You should buy a copy of Internal Time if: you’re a person who sleeps.  Or a person who likes learning.

Reading Tips: Readers will likely get more out of this book if they’re already familiar with the general principles of evolutionary biology; at the very least, I’d recommend flipping through the trait adaptivity mental model.  Some understanding of genetics would also be additive, but isn’t a hard prerequisite. 

Some of the science is inherently technical, but unlike, say, James Gleick in The Information, Roenneberg actually does a good job of trying to help the reader understand, and it’s worth rereading the technical pages several times (or rereading the whole book a few times) to deeply understand the underlying principles.

Pairs Well With: This twenty-minute presentation and interview.

Dr. Matthew Walker’s “Why We Sleep” (Sleep review + notes) – a more general-purpose book on the fascinating (and hugely important) science of sleep.  I bought all ACM clients of Why We Sleep to celebrate the launch of PAA; I’ve called it “the most important book of the century.”

Peter Godfrey-Smith’s “Other Minds” (OthM review + notes), or Jennifer Ackerman’s “ The Genius of Birds” ( Bird review + notes).  Other great examples of  trait adaptivity and how it can change over time.

Cass Sunstein and Richard Thaler’s “Nudge” (NDGE review + notes).  One of the most interesting elements in Internal Time is Roenneberg’s cogent and insightful analysis of  culture / status quo bias and why the morning myth has gotten “stuck” in our cultural consciousness.  Nudge provides a fascinating exploration of some of the mechanisms underlying this.

Reread Value: 5/5 (Extreme)

More Detailed Notes + Analysis (SPOILERS BELOW):

IMPORTANT: the below commentary DOES NOT SUBSTITUTE for READING THE BOOK.  Full stop. This commentary is NOT a comprehensive summary of the lessons of the book, or intended to be comprehensive.  It was primarily created for my own personal reference.

Much of the below will be utterly incomprehensible if you have not read the book, or if you do not have the book on hand to reference.  Even if it was comprehensive, you would be depriving yourself of the vast majority of the learning opportunity by only reading the “Cliff Notes.”  Do so at your own peril.

I provide these notes and analysis for five use cases.  First, they may help you decide which books you should put on your shelf, based on a quick review of some of the ideas discussed.  

Second, as I discuss in the memory mental model, time-delayed re-encoding strengthens memory, and notes can also serve as a “cue” to enhance recall.  However, taking notes is a time consuming process that many busy students and professionals opt out of, so hopefully these notes can serve as a starting point to which you can append your own thoughts, marginalia, insights, etc.

Third, perhaps most importantly of all, I contextualize authors’ points with points from other books that either serve to strengthen, or weaken, the arguments made.  I also point out how specific examples tie in to specific mental models, which you are encouraged to read, thereby enriching your understanding and accelerating your learning.  Combining two and three, I recommend that you read these notes while the book’s still fresh in your mind – after a few days, perhaps.

Fourth, they will hopefully serve as a “discovery mechanism” for further related reading.

Fifth and finally, they will hopefully serve as an index for you to return to at a future point in time, to identify sections of the book worth rereading to help you better address current challenges and opportunities in your life – or to reinterpret and reimagine elements of the book in a light you didn’t see previously because you weren’t familiar with all the other models or books discussed in the third use case.

Page 2: universal time as a modern concept didn’t exist until trains made travel fast enough for sun time to not be helpful.  Roenneberg’s book analyzes the interaction between three times or “clocks” – that set by the sun, that set by society, and that set by your internal biology (the “internal time.”)

Page 4: on how the engine works versus turning it on:

“I soon realized that the true aim of my interests concerned humans and that physics just didn’t get me any closer to understanding them.”  

Kind of an emergence thing.  Also, Roenneberg faced Thaler’s challenges because he didn’t fit into a neat little box…

Page 6: setting aside the subject matter, I love Roenneberg’s approach.  First of all, unlike Daniel Kahneman, Roenneberg is a capable of being a rigorous scientist without losing all sense of good writing; unlike James Gleick, Roenneberg is capable of educating rather than insulting a lay audience.

Roenneberg notes that:

“the drawback of traditional learning has always been the dissociation between the theory and its application ‘Why do we have to learn this?’ is probably one of the most frequent and justified questions teachers hear.’”  

Roenneberg’s book is very long utility and very short non-utility.

Page 10: Mental note: I need to get me a t-shirt that says “Early to rise and early to bed makes a bird healthy, wealthy, and dead.”

Pages 12 – 14: two separate (but interrelated) concepts are an individual’s chronotype and their natural sleep duration, both of which vary.  Sleep duration represents the length of time an individual sleeps, if given the opportunity.  

Chronotype is measured by the midpoint of an individual’s sleep, to account for differences in sleep duration among individuals.  So, for example, I typically sleep somewhere in the neighborhood of nine hours from 3 AM to 12 PM.  

So my “ chronotype” would be 7:30 A.M., which is definitely on the “late” side of the curve Roenneberg presents, but (surprisingly) not as late as you might imagine.  Roenneberg, later, notes that social time is too early for about 60% of the population, for a variety of reasons.


*Note: in the twenty-minute linked presentation, Roenneberg clarifies that for most working adults, sleep duration can be measured on neither weekdays or weekends, because many, particularly late chronotypes, get way too little sleep on weekdays and need weekends to catch up, and most people are generally chronically sleep-deprived.  This was certainly true for me when I wasn’t able to control my own sleep schedule as I do now.

See also, of course, Dr. Matthew Walker’s “Why We Sleep” (Sleep review + notes) – sleep loss is an epidemic.

Pages 17 – 22: Roenneberg brings up (before summarily dismissing) the flawed/anachronistic paradigm wherein “practically every culture declares early risers as good and late risers as bad people.”


He brings up (briefly; discussed in more depth later) the concept of trait adaptivity: i.e. the reason we have biological clocks in the first place is because there’s an evolutionary advantage to having them, but when circumstances change far more rapidly than evolution (as has happened with modern industrialized society, wherein our exposure to natural light during the daytime has been dramatically reduced and exposure to artificial light well beyond dark has been dramatically increased), curious things can happen – like the fact that most of us are now far later chronotypesfrom a phenotypic perspective than we would have been historically (assuming equivalentgenotypes).

It’s worth quoting Roenneberg’s dry retort to the supposed moral superiority of morning people at length, because via inversion, it pretty perfectly summarizes the trait-adaptivity argument for why the argument may once have held, but doesn’t any longer:

“As long as all individuals have similar [chronotypes],  the earliest bird has an advantage over anyone getting up later.  This was probably true for most preindustrial societies; hence the persistence of the early-bird proverbs.  [But under modern circumstances]… the temporal chicken-and-egg problem starts to apply […] [extremely] late chronotypes would still be awake [before early birds rise].  There is no reason why these extreme late types couldn’t gather all the mushrooms before the early risers arrived […]

This myth that early risers are good people and that late risers are lazy has its reasons and merits in rural societies but becomes questionable in a modern 24/7 society.”

culture / status quo bias.  See also my note on pages 148 – 149.  A significant body of research – for example, I love Chris Barnes’ writings in HBR on the topic (1, 2, 3) – has confirmed the commonsense notion that there’s widespread societal discrimination against late chronotypes, despite research indicating that the majority of the population is a late chronotype.  More to come on this from Roenneberg later in the book.

(It’s worth noting that there’s also some discrimination against early types, though not as much – apparently they have trouble sleeping in, so it’s really hard on them to go out with friends in the evenings, because they can’t catch up on sleep on the weekend like late types.)

Pages 26 – 30: Roenneberg notes that our sleep/wake cycles are modulated by two separate controls: our internal clock telling us what time it is, and how tired we are.  Ironically, one of the hardest times to fall asleep, per the research, is immediately before the time we begin to become capable of falling asleep.

This explains the phenomenon many people experience of lying awake, exhausted, yet not being able to sleep.  (This is what happened to me every weeknight when I had a job, unless I took, as my doctor quipped the first time I met him, “enough Benadryl to tranquilize a horse.”)

Pages 32 – 33: French astronomer Jean Jacques d’Ortous de Mairan (almost as challengingly named as Mihaly Csikszentmihalyi) discovered in 1729 that his mimosa’s leaves lifted to face the sunlight… even if the plant was kept in the dark.  Clearly, the plant somehow knew when it was light outside.  But how?

Page 35: In an example of “the future is here, it’s just not evenly distributed” (one to many), Roenneberg notes that de Mairan correctly identified some phenomena that it took 200 years for scientists to re-engage with.  Reminds me a bit of poor Mendel’s peas…

Pages 38 – 40: a fascinating example of a test subject in a free-running environment ending up with a two-day circadian rhythm.

Pages 42 – 44: it turns out that our biological functions (such as hormone production and temperature) and our sleep times are synchronized… but they don’t have to be; they can desynchronize under certain conditions.  These subjects, surprisingly, didn’t notice – they thought their days were normal length.

Pages 45B – 46: Back to trait adaptivity – Roenneberg queries, on behalf of the reader: well,

why [was] evolution so sloppy as to create a biological clock that cannot keep track of time properly?”  

The answer is that it’s the environment, rather than the clock, that’s malfunctioning (from an evolutionary perspective).  Roenneberg notes that “the biological clock did not evolve in a time-free world” – in other words, the experiments were essentially seeing what the biological clock did under constant light conditions, a completely unnatural set of external circumstances in (most) of the external world.

Page 49: with a 25-hour body clock and a 24-hour external clock, in the absence of light to synchronize, the desynchronization can lead to challenges.  This often happens to the blind. (More on non-24 and blindness here.)

Pages 50 – 51: Roenneberg provides a useful overview of human vision: light goes through the lens in our eyes; it hits the back of our eye (the retina), which sends the data to the brain via the optic nerve.  Near behind the bridge of our nose is the optic chiasm, where the nerves cross and go into the other side of the brain for cross-processing to put the image together.

Rods are grayscale; cones compute color.  There is a new type of receptor, melanopsin, which is similar to how amphibians change their skin color.  Can’t tell whether or not it’s similar to what is described about octopus color-changing on pages 108 – 112 of Peter Godfrey-Smith’s wonderful Other Minds ( OthM review + notes).  Anyway, melanopsin is what feeds information to the clock.

Pages 57 – 59: In lower animals, the clock is in the pineal gland (which produces melatonin).  Light can sometimes directly hit the pineal gland in other animals. The pineal gland produces melatonin, the chemical signal for darkness.  In humans, the clock is in the suprachiasmatic nucleus, which is tiny (only twenty thousand cells, apparently). It can be transplanted, apparently.

Pages 62 – 63: Roenneberg starts to get into the science of entrainment and how the clock actually works: it’s actually the length of our internal day/rhythm, rather than the timing, that is genetically controlled.  Shorter days (for reasons we’ll see later) get entrained to “early” chronotypes; longer days get entrained to “late” chronotypes.  Also, most of us are late, having longer-than-24-hour days, if I read correctly.

Pages 64 – 65: Notes on the genetics of the tau hamster’s clock gene.  Also some hamster incest.  (This is surprisingly common in genetics research, it seems.)

Pages 68 – 69!: Mormons are, among other things, apparently useful for genetic research because of their large families and well-kept family trees.  See also pages 279 – 281 of The Gene where Mormons are used to study linked genes.

Anyway, a nice example of multicausality here – discussing a large, close-knit Utah family (statistically, they’re Mormons!) with ASPS/ASPD (advanced sleep phase syndrome, or disorder), he notes that in them, the clock protein cannot be modified as easily, whereas in the tau hamster, the protein was normal but the enzyme modifying it wasn’t.  Two different kinds of mutations can lead to the same result.

Also, Roenneberg is very focused on the human side of this: when he discusses the data from his research with a colleague, their (very unscientific) response is surely the biological clock is only an issue for very sensitive people.”  Roenneberg takes a lot of issue with this sort of ignorance and bias later.  

Page 70: Not original or unique, but Roenneberg tells the Max Planck chauffeur anecdote here.  Whether or not it’s true, it’s fun.

Page 72: A nice example of feedback effects: the biological clock follows the pretty standard Central Dogma approach.  The clock gene DNA is transcribed to mRNA, which is translated into a protein.  When enough protein has been made, it ends up inhibiting mRNA transcription, and eventually all of the proteins are “destroyed”… and the cycle starts again.

That’s actually an oversimplification; there’s not just one gene or protein, but directionally that is how it works.

Pages 75 – 77: In an anonymized version of a real incident (see the notes), “Oliver” the doctoral student couldn’t get a certain experiment to work because he was a lark, while the postdoc who had originally done the experiment was an owl…

Page 79!: … why didn’t the experiment work until Oliver stayed up all night?  Because, as referenced earlier, hormone production is also coupled to the circadian rhythm.  This is no laughing matter; Roenneberg notes explicitly that “the point of this chapter is to show how profound the influence of circadian timing is.”  

He points out that this is important for drug delivery; certain drugs are more or less effective at certain times of day.  But of course, these times of day aren’t absolute – they’re relative to the individual’s chronotype, i.e. internal time.  So, for example, Roenneberg cites the example of patients going in for blood labs at 8 AM after an all-night fast… I’m not gonna get up at 8 for that, but going at noon or 1 PM is probably about the same for me, considering that my one-o-clock (biologically) is equivalent to that of a median-chronotype person who wakes up at 7 or so.

Page 80: Quantification: 15 to 40% of genes are switched on and off at different times of the day.  Metabolism, under other systems, is “under the control of the circadian clock.”  Circadian rhythms are present not just in the brain, but in other organs, where they can be controlled by other things than light.

Page 84?: kind of off topic but I found it funny that the scientists endearingly named their dinoflagellates “Gonies” (nickname for Gonyaulax).  It reminded me of the “love them because you care for them” dynamic discussed in, of all things, All Joy and No Fun.  I kind of want to return to this at some point in the context of intrinsic motivation

Page 86: This chapter is pretty stellar contextualization of evolutionary biology, i.e. trait adaptivity, in understandable terms; it’s a little bit like an abbreviated version of Peter Godfrey-Smith’s “ Other Minds” OthM review + notes).  I can’t do this justice without just scanning images of the whole pages here, so I won’t.  It’s a gem worth pulling out the book and rereading.

Page 93: In addition to the variables discussed earlier, body temperature (specifically, a low body temperature) helps maintain sleep even past the point of our sleep pressure incentivizing it less.  This is why, I think, a lot of people like to sleep cold (… I don’t like to be that cold, although I don’t like to be hot either. But I’m weird.)

Page 95: he briefly mentions “internal lunchtime” here and I think it’s interesting, from a biological perspective, that I more or less seem to have a similar eating schedule no matter when I get up.  When I worked 9 to 5 and had to get up in the morning, I was hungry during the morning and snacked, then had lunch at 11 and an afternoon snack and then dinner at a reasonable social hour.  

Now, I pretty much do the same thing getting up at 11 or noon or 1, minus the snack. (Post the age of, like, eleven or twelve, I’ve never been a breakfast person.)

If I have to get up really early to go somewhere, I usually do try to scarf down a muffin or something, but it’s not because I’m hungry – rather, because otherwise I’ll basically just die before lunchtime from lack of glucose to the brain.  So I play both Ann and Ann’s mother (from one of the book’s first chapter-opening case “stories.”)

I kind of want to figure out why this is and what’s going on metabolically.  I know it does mean that 16/8 is particularly workable for me…

Page 98, Pages 100 – 102: Roenneberg reviews chronotypes: babies/kids have early chronotypes; teenagers have late chronotypes, and we move back toward early as we age from there.  Boys, interestingly, have later chronotypes than girls for much of their lives. Roenneberg jokes that this is why men marry younger women – so they can have breakfast together! (He’s kidding.)

Some lovely graphs and some interesting notes on statistical sample sizes for determining various things.

Page 105: Here, Roenneberg references what I mentioned earlier: the one challenge for larks is that early chronotypes seem to have a real hard time sleeping in to catch up on sleep (which latechronotypes do near-universally).  So, they deserve some empathy too… a little… maybe.  If they’d stop ruining the world for the rest of us 😛

Pages 107 – 109, Pages 110 – 112: I sort of want to photocopy these pages and just walk around handing them out as a public service announcement.  Since Roenneberg’s publisher would probably not love me for doing that, the short version is that:

First of all, as you might imagine, a lot of high school (and college) students don’t function well in the mornings.  This was certainly the case for me.  Or, as Dr. Matthew Walker puts it in Why We Sleep (Sleep review + notes):

“Asking your teenage[r] to go to bed and fall asleep at ten p.m. is the circadian equivalent of asking you, their parent, to go to sleep at seven or eight p.m..  No matter how loud you enunciate the order, no matter how much that teenager truly wishes to obey your instruction, and no matter what amount of willed effort is applied […] the circadian rhythm of a teenager will not be miraculously coaxed into a change.

Furthermore, asking that same teenager to wake up at seven the next morning and function with intellect, grace, and good mood is the equivalent of asking you, their parent, to do the same at four or five a.m.

[…] teenagers’ sleep patterns [… are] non-volitional, non-negotiable, and strongly biological.  We parents would be wise to accept this fact […] and praise it, lest we wish our own children to suffer developmental brain abnormalities or force a raised risk of mental illness upon them.”

Second, even otherwise smart/intelligent people experience a schema bottleneck when it comes to understanding and empathizing with late chronotypes: Roenneberg cites examples ranging from a physics teacher to politicians who make arguments akin to the “invisible handwave” economists used to dismiss Richard Thaler’s work.

This is in spite of overwhelming empirical evidence – here, for example, is a review of 38 studies that finds that later [high school] start times also generally correspond to improved attendance, less tardiness, less falling asleep in class, better grades, and fewer motor vehicle crashes.”

Roenneberg found the level of discussion among teachers and politicians to be frighteningly low and shallow.” In the middle of other arguments, one, for example, noted that students could basically just go to bed earlier… notwithstanding Roenneberg’s exhaustive data to the contrary.

Opponents, for example, cited logistical concerns about bussing students, as if changing bus schedules was more important than ensuring a proper education and (to reference the study above) reducing potentially fatal motor vehicle crashes.  (Daylight Savings Time predictably leads to an increase in car crashes on Monday due to sleep deprivation; note that every weekday represents meaningful sleep deprivation for most teenagers.)

Roenneberg goes on to note that when students are brought into a sleep laboratory at their normal school start time, many display symptoms of narcolepsy.  Roenneberg’s conclusion?  Traditional school start times “blatantly discriminate against […] the majority of teenagers.  This isn’t a good compromise […] early types, however, could still perform just as well is schools started later.”  

This is also the case for the workplace, incidentally.

The sad thing is that this schema bottleneck is so deeply engrained in our culture that I’ve had little success convincing even most of my close friends and family that I’m not making this shit up (if you’ll pardon my French).  Somehow, they look at the following two pieces of data:

A: I’ve aced every standardized test I’ve ever taken; I graduated from high school at 17 with two years of college done at a 4.0 GPA, I started working full-time my final year in college while stilltaking a full-time courseload and still graduated summa cum laude while getting a perfect performance review at work… and so on and so on, demonstrating that lack of “ willpower” or “ grit” are, directionally, not usually problems for me.

B: I claim that no amount of effort or willpower or structural problem solving has, in my life, ever allowed me to be a functional human being in the morning.

… and they come away with the conclusion that “if you just tried a little harder” or “drank less coffee” or “went to sleep earlier,” I’d be able to get up at 8 and be awake and functional like everyone else.

Like hell I would.  I’ve tried. It doesn’t work.  I’ve been adamant about this. And nonetheless my own mother still doesn’t fully believe that, along with probably half of my closest friends.

It’s a very strange situation because the quasi-moral puritanism around the supposed inherent superiority of mornings is so strong that I think even if you quantitatively proved to most business managers that their employees would be 20% more productive (not a stretch) if allowed to come in two hours later… the managers would still say no.  (See the referenced Chris Barnes piece in HBR on flextime.)

Pages 118 – 124: Roenneberg now details the “entrainment” process by which our internal clocks (of varying lengths) synchronize to the external clock of the earth’s rotation.  Similar to but different from feedback effects, the influence of the “zeitgeber” (the environmental cue – light, in this case) varies depending on the time of the day.

Setting internal dawn (i.e., the time we wake up) at zero, light during the first half of the day compresses the length of the day (i.e., causes us to feel sleepy earlier), while light during the second half of the day (i.e. evening and night) expands the length of the day (i.e., keeps us up later).

The way the math works (see the charts), people with short internal clocks end up becoming early types, people with long internal clocks end up becoming late types.  

Later, Roenneberg discusses how, in the industrialized world, this has resulted in us becoming later types: during the daytime, we don’t receive much light (he notes in the linked presentation that daylight is orders of magnitude stronger than internal light).  

At night, however, we receive lots of light from screens and lights that wasn’t there previously… this makes us later chronotypes. People in big cities, exposed to more light, are fairly predictably later chronotypes as well.

The interesting thing is that, again, to a large degree, this is a trait adaptivity issue – I’ve noticed (to my astonishment) that when I go camping/backpacking, not only am I perfectly able to get up with the sunrise and fall asleep reasonably soon after sunset (or, at least, significantly earlier than I would at home), but I don’t have any of the grogginess that I would at home.

Of course, attempting to eliminate all blue light exposure after sunset, and being outside all day during the daytime, is hardly practicable for a white-collar worker.  But it is a nice real-world example.

Page 127: this “frequency demultiplication” thing is really interesting but I don’t understand it.

Pages 135! – 136!: Roenneberg discusses jetlag… he notes, importantly, that “cognitive states (like vigilance, alertness, and attention) and skills (like motor coordination, performing simple calculations, or memory tasks) are as much under the control of the body clock as sleep and wakefulness.”

I can attest that this is the case: when I had to work 9 to 5, I pretty much sat at my desk vaguely trying (not very hard) to look like I was working until about 2 or 3.  Then I finally woke up enough to do a bit of work, and did most of my real work when I got home in the evenings and (after a nap) was finally lucid enough to do something productive.

It’s not a stretch to state that my productivity increased by an order of magnitude when I started working for myself and got to un-wreck my sleep schedule.

Pages 142 – 143: Here, Roenneberg notes the meaningful sleep deprivation experienced by late chronotypes on workdays as a result of early start times, and the modest sleep deprivation experienced by early chronotypes on weekends as a result of social pressure to stay up / go out late on Fridays/Saturdays.  

Pages 144 – 147: Roenneberg goes deeper into the topic, graphically presenting sleep behavior for a variety of chronotypes under a variety of conditions.  He notes that “work times are too early for 60 percent of the population.”  This leads to an odd scalloped-shape graph where late chronotypes are abruptly awoken on work days by their alarm clock, truncating their sleep, and leading to meaningful “catch-up” sleep on the weekends.  The standard workweek, for late chronotypes, is roughly equivalent to permanent jetlag, i.e. commuting across the United States timezones for the workweek.

Pages 148 – 149: Again going to quote at length because I think it’s important to be able to reflect on Roenneberg’s takeaways from a career in chronobiology without my interpretation getting in the way:

“I am often asked whether we cannot get used to given working hours merely through discipline and by confining our sleep habits to certain times.  The assumption inherent in this question is that the human body clock can synchronize to social cues.

I tend to find that any such questioner, who usually also displays a somewhat disdainful tone toward the weakness of late chronotypes, is an early type – someone who has never experienced the problems associated with the scallop-shaped sleep-wake behavior of late chronotypes.”  

Sleep x agency  willpower.  Dr. Matthew Walker comes to similar conclusions in “ Why We Sleep ( Sleep review + notes):

“When a night owl is forced to wake up too early, their prefrontal cortex remains in a disabled, ‘offline’ state.  Like a cold engine after an early-morning start, it takes a long time before it warms up to operating temperature […]

Sadly, society treats night owls rather unfairly on two counts.  First is the label of being lazy […] night owls are not owls by choice.  They are bound to a delayed schedule by unavoidable DNA hardwiring. It is not their conscious fault, but rather their genetic fate.

Second is the engrained, un-level playing field of society’s work scheduling, which is strongly biased toward early start times that punish owls and favor larks.  Although the situation is improving, standard employment schedules force owls into an unnatural sleep-wake rhythm […]

Most unfortunately, owls are more chronically sleep-deprived [than larks]. […] greater ill health caused by a lack of sleep therefore befalls owls, including higher rates of depression, anxiety, diabetes, cancer, heart attack, and stroke.”

See also, here, Chris Barnes’ research on managers preferring larks to owls even if they both have the exact same performance.

In a later 2015 piece, Barnes summarized:

supervisors tend to assume that employees who start and finish work late (versus early) are less conscientious and lower in performance, even if their behavior and performance is exactly the same as someone working an early riser’s schedule”

Great example of a schema bottleneck as well as a status quo bias and  product vs. packaging: if, in an alternate universe, everyone were able to get enough sleep and early chronotypes didn’t enforce blatant systematic discrimination against late chronotypes, we’d be appalled by the proposition of intentionally forcing more than half the population to be routinely sleep-deprived… but because that’s the way things have historically been done, we stick to the morningness heuristic, despite circumstances that have dramatically altered our natural chronotypes.

Roenneberg also goes deeper into some of the chronic consequences of  “social jetlag.”

Pages 154 – 155: The state of Saxony-Anhalt in Germany gets up earlier than anyone else.  A product of their diligence and stoicism? Nope – it’s because the sun rises earlier in the east than the west, a trend that (Roenneberg empirically and exhaustively demonstrates) pretty consistently influences the time people wake up relative to their time zone.

Page 158: You don’t need Excel to come up with this line of best fit.

Pages 160 – 161: Roenneberg notes the interesting fact that we now attempt to conform our body clocks to “social time” rather than “sun time.”

Page 164: The anecdote here about the twins is interesting.  (And not just because twins, like Mormons, turn out to be particularly useful for science!)  It really drives home the trait adaptivitymodel present throughout this book: our body clock did not evolve in an environment that looks anything like the modern-day environment; as such, it’s not surprising that it’s pretty poorly adapted to conforming to an arbitrarily-set schedule that’s nothing more than a heuristic holdover from an era in which it made sense.

Pages 166 – 167: To get a little more scientific about it, what’s happening today (as Roenneberg explains at length) is that the natural variation in chronotypes is amplified by the substantially decreased strength of the “zeitgeber” (the external environmental clue – in this case, light.)  Paradoxically, the modern environment makes naturally early chronotypes earlier and naturally late chronotypes later.

Roenneberg also notes the discrepancy between zeitgebers (and, concomitantly, people’s chronotypes) in towns vs. the countryside; there is a completely perfect explanation here for why I wake up with the sun and feel totally fine when I’m camping, whereas I felt like I’d been hit by a Mack truck every morning when I turned off my alarm clock and rolled out of bed for work.

Page 171: more on the strength of the zeitgeber; driving the above-referenced points home, Roenneberg notes that the strength of the zeitgeber in industrialized modern settings is 200 times less than for those who work outdoors.

Page 179 – 182: at this point, nobody should be shocked that Daylight Savings Time, like most other time-related inventions, is harder for late chronotypes than early ones: late chronotypes still haven’t adapted by four weeks after DST.  Roenneberg, unsurprisingly, doesn’t seem to be much of a fan.

Pages 188 – 189: Roenneberg goes deeper into some of the potential health consequences of living out of synch with your chronotype, here delving deeper into shift work and the potential role of melatonin in tumor suppression.  

Roenneberg doesn’t really seem to believe the melatonin-as-antioxidant hypothesis, at least not as much as it’s touted; this would appear to be the consensus (ex. This page from Memorial Sloan Kettering).  Others, like Russel Reiter, seem to be all-in on it.

Page 190!: bringing it back to the more general discussion, Roenneberg notes that:

“In view of the lateness of most people in our modern societies, one could argue that a majority of the workforce is scheduled in a permanent early shift when they work from nine to five.”

Pages 197 – 199: Another interesting example of schema here: men accurately assess their wives’chronotypes, but women don’t accurately assess their husbands’ chronotypes, because men typically go to sleep when their wives do.

There’s also a good contrast bias and salience bias / vividness heuristic here: given that most people are most prominently/saliently exposed to their partner’s chronotype, many people tend to think they’re earlier or later than they really are.

Pages 203 – 205: on pre-modern sleep patterns, which (directionally) I’ve observed to be more directionally the case on camping trips.

Page 207: here’s a morbid curiosity from Roenneberg: mood reaches its lowest point in cold, dreary seasons, but that’s not when suicide peaks.  Nope, that would be in midsummer… why? “The actual act of suicide […] takes a level of energy that depressed individuals cannot muster during their most depressed times of the year.”

Pages 215 – 218: two things: first, back to trait adaptivity.  Here (and moreso in his presentation), Roenneberg makes explicit the idea that there’s a lot of selection bias at play: people who end up in executive roles, for example, tend to be early types because that’s often required by the current culture.  They then, of course, perpetuate that culture.

Second, another dry quip.  Commenting on a study finding that sleep deprivation can lead to medical interns making 36% more “serious medical errors” while providing patient care, Roenneberg notes: “It’s not surprising that someone who works for up to seventy-two hours without noteworthy rest makes more mistakes, but what seems like common sense is worthless without a quantitative basis provided by a properly designed study.”  I can’t tell if he’s being snarky or serious – in context, I’m guessing snarky – but it’s hilarious either way.

See also, of course, Dr. Matthew Walker’s “Why We Sleep” (Sleep review + notes).

Pages 219 – 220: Roenneberg discusses the genetic basis for sleep duration requirements.  He notes the (commonsense, but perhaps worthless without quantitative study!) tendency of toddlers to be unbearable if they’re sleep-deprived.  At the extreme, he discusses children suffering from a particular genetic disorder (Smith-Magenis syndrome) that was thought to cause (among other symptoms) “severe behavioral pathologies.”  

The genetic disorder does cause a lot of challenges, but the behavior actually isn’t one of them (directly, anyway).  The kids are actually just sleep-deprived: in some cases, the syndrome can lead to an inverted melatonin production, i.e. during the day at night.  Treating this and allowing them to sleep properly led to both them and their caretakers having a higher quality of life. Fascinating.

Disaggregation /  multicausality.

Pages 230 – 231: Roenneberg concludes with an interesting diversity argument and some take-home conclusions: “let’s make the most of the chronotype differences within our species […] we would be less tired and more cheerful […] we would perform better […] we would be healthier.  Our work schedules have to acknowledge that most of us are no longer farmers.”

Page 237: In the endnotes, Roenneberg mentions Modafinil as one of the drugs that, quote, “make people feel quite normal in spite of not having slept enough.”  Modafinil, unsurprisingly, happens to be really popular on Wall Street, from what I’ve heard.


First Read: 2017

Last Read: spring 2018

Number of Times Read: 3

Planning to Read Again? um, yeah!

Review Date: spring 2018

Notes Date: spring 2018