Professor ~ Applied evolutionary anthropology | Meta-tribalism | Anti-entropy
Toronto, Ontario
Joined July 2011
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The Sleepless Ape: The Story of Sleep in Human Evolution is officially out today!
To celebrate, here are some of my favorite clips and images from the fieldwork and research that shaped it — chimp nests, hunter-gatherer sleep camps, and the evolutionary puzzle of why humans became the “sleepless ape.”
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Humans sleep less than any other primate studied. How did we evolve to do so much with so little?
That question is at the heart of my book, The Sleepless Ape, and this new feature by Kurt Kleiner in U of T Magazine.
One idea I explore: our ancestors’ move from the trees to the ground transformed sleep. Fire, shelter and the protection of a group may have helped make deeper, more efficient sleep possible—freeing time for learning, strengthening relationships and developing new technologies. Our research with Hadza communities in Tanzania adds another piece to that story. With naturally staggered sleep schedules, there was almost always an adult awake. Individual differences in sleep timing may have helped keep the group safe. I find this possibility fascinating: our capacity to sleep securely may be deeply connected to our capacity to cooperate.
Thank you to Kurt Kleiner and U of T Magazine for exploring how sleep may have helped shape our species. Read the feature: “Sleep Is Essential. So Why Do We Need So Little?”
magazine.utoronto.ca/researc…
Who is really keeping whom up at night — you, or your dog?
I’m thrilled to see this new UTM story on work led by Ming Fei Li and Lavania Nagendran, with Christopher Kiru, Lauren Schroeder, and me, now out in PLOS ONE.
We followed 25 dog owners and 38 dogs over four weeks using actigraphy sensors to examine nighttime movement patterns. The finding I love most: co-sleeping with dogs did not meaningfully disrupt objectively measured human sleep duration or efficiency. But the relationship is wonderfully reciprocal. In many human-dog pairs, nighttime activity was linked — and more often, humans moved first, with dogs following.
So the old question “is my dog disturbing my sleep?” may need a mischievous rewrite: “am I disturbing my dog?” The study also gets at something deeper about the human-dog bond. Sleep is a vulnerable state. Who we allow near us at night says something about trust, safety, routine, and interspecies intimacy.
Congratulations to Ming Fei and Lavania on this beautiful work. UTM story:
utm.utoronto.ca/main-news/yo…
Original paper: journals.plos.org/plosone/ar…
What if loneliness changes the way the sleeping brain listens to the night?
Grateful to John McCarthy for drawing on The Sleepless Ape in this Psychology Today piece on loneliness and the evolution of sleep. One of the stranger things about modern sleep is how solitary it has become. For most of human history, sleep was embedded in a social world: shared sleeping spaces, nearby kin, firelight, overlapping vigilance, and the quiet reassurance that other bodies were close.
From that evolutionary angle, loneliness is more than a feeling that happens during the day. It may shape the physiology of the night. If the social world feels uncertain, the sleeping brain may remain more vigilant. Poor sleep and loneliness can then begin to reinforce each other — biologically, emotionally, and socially.
This is one reason I think sleep is best understood as ecological. It belongs to bodies, relationships, safety, place, and culture.A thoughtful read on a connection we should take seriously:
psychologytoday.com/us/blog/…
Vancouver friends: I am giving a U of T alumni talk on Oct 6.
The Sleepless Ape: What Human Sleep Reveals About Evolution, Health and Modern Life.
Rosewood Hotel Georgia. Free. Remarks at 6:30 PM PDT.
We are the sleepless apes. Compared with our closest primate relatives, we sleep less, yet our sleep is unusually intense, flexible, and social. In this talk I take that story from great ape sleeping platforms to Hadza camps, and ask what it still means for how we live now.
The event is sold out. If you want in, join the waitlist through the alumni page (or email regional.programs@utoronto.ca). There is also a 40% book offer on The Sleepless Ape for pickup and signing at the event.
alumni.utoronto.ca/events/u-…
What can hunter-gatherer sleep teach us about our own restless nights?
Grateful to Amanda Ruggeri for drawing on our conversations — and for mentioning The Sleepless Ape — in this new BBC Future piece on sleep, temperature, light, social time, and hunter-gatherer communities.
One of the great lessons from studying sleep cross-culturally is that human sleep is deeply ecological. It responds to heat and cold, sunrise and firelight, work and rest, safety and social life. Our ancestors did not sleep in a sealed box with a thermostat, blackout curtains, phone alarms, and a glowing rectangle beside the bed. They slept in living environments.
That wider evolutionary frame changes the question. Sleep becomes less of a rigid nightly performance and more of a flexible biological system — one shaped by bodies, seasons, communities, and place.
A thoughtful read for anyone interested in what ancient sleep can teach modern life:
bbc.com/future/article/20260…
Speakers Spotlight asked a few of us for one piece of advice on feeling and performing at your best.
Here's mine:
Your circadian system evolved under bright mornings and dark nights. Most of us now get the reverse: dim indoor days, bright screens after dusk. That mismatch is fundamentally a signal problem.
Get outside within the first hour of waking. Twenty to thirty minutes of actual daylight. That single cue does more for stable energy than most of the optimization stack.
And stop to read the other experts on the roundup -- all worth reading! Physicians and performance scientists, same question, different levers.
speakers.ca/2026/09/the-doct…
Kirkus gave The Sleepless Ape a “GET IT” verdict — and called it “eye-opening.”
I’m grateful for the review, especially because the book asks a question that sounds simple until you put it beside the rest of the primate order: why do humans sleep so little?
The answer runs through chimpanzee nests, Hadza camps, firelight, lookouts, REM sleep, social sleep, and the strange fact that our species became both the shortest-sleeping primate and one of the most cognitively flexible animals on Earth.
Sleep is often treated as a private wellness variable. I see it as one of the great evolutionary clues hiding in plain sight — a nightly fossil of how humans became human.
Read the Kirkus review here: kirkusreviews.com/book-revie…
“Social commentaries argued that sharing a bed polluted the air and undermined social respect, making it not only unhygienic but also immoral.” Review of The Sleepless Ape by @Primalprimate
kirkusreviews.com/book-revie… #kirkusreviews
David Samson retweeted
“Social commentaries argued that sharing a bed polluted the air and undermined social respect, making it not only unhygienic but also immoral.” Review of The Sleepless Ape by @Primalprimate
kirkusreviews.com/book-revie… #kirkusreviews
Is sleep our secret weapon?
I joined RNZ’s Saturday Morning to talk about one of my favorite evolutionary puzzles: humans sleep less than any other primate, yet our sleep is unusually intense, flexible, and packed with REM.
That paradox sits at the heart of The Sleepless Ape. Why would a species with such large cognitive demands evolve to spend less time asleep? Part of the answer may be that humans became astonishingly good at controlling the conditions around sleep: fire, shelter, social vigilance, safer sleeping sites, and eventually whole cultural worlds built around the night.
We also talked about Hadza sleep, chimpanzee nests, morning light, circadian biology, and why the familiar story of a modern “sleep epidemic” gets more interesting when we look across cultures and evolutionary time.
Many thanks to RNZ for such a thoughtful conversation.
Listen here:
rnz.co.nz/national/programme…
New article out in National Geographic: “Should You Share a Bed With Your Baby?”
This one feels especially meaningful. More than a decade ago, National Geographic helped fund my fieldwork on human sleep. Now some of those questions — about infant sleep, proximity, safety, culture, and evolutionary mismatch — have come home as an article in National Geographic.
I wrote about a difficult tension: the ancient human drive for closeness at night, and the risks created by modern sleep environments. Across much of human history, infant sleep was social: babies slept within a caregiver’s sensory radius. Today, parents are navigating that inherited drive in bedrooms filled with soft mattresses, pillows, duvets, sofas, exhaustion, medications, smoking exposure, and other modern risk factors.
The deeper story is one of evolutionary mismatch. Human infants evolved in a world of proximity, sensory contact, and shared vigilance. Modern safety guidance has to reckon with that biology while also giving parents clear, practical ways to reduce risk on real nights, when fatigue and caregiving collide.
This is personal for me, too. When our son was born, my wife and I felt that ancient tug toward closeness after many sleepless nights. After weighing the evidence, the risks, and the realities of those bleary first months, we chose a breastsleeping arrangement that helped us keep him close while staying attentive to safety. We've done it since day one for our second born.
As I wrote in the article: "I am an evolutionary anthropologist, not a clinician.... Our experience does not prove that the arrangement was safe or make it a recommendation for another family. But it helped me understand why families keep choosing it. For us, it was not an ideology. It was a way through the night."
nationalgeographic.com/healt…
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New piece in IFLScience on my recent Journal of Human Evolution paper:
“Fire May Have Transformed Humans From Daytime Creatures Into 24-Hour Animals… Kind Of Like Lemurs.”
The article gets at one of the central ideas behind the human diel flexibility hypothesis: humans are basically diurnal animals, but we became capable of extending activity into the night when the social and ecological payoffs were high enough.
Fire was central. It changed the sensory landscape after sunset, reduced predation risk, extended social time, enabled warmth and cooking, and created a protected space for conversation, ritual, planning, teaching, and vigilance.
In other words, the night became usable.
The key nuance is that this does not mean humans evolved to be fully nocturnal. Our circadian system remains strongly anchored to the solar day. But compared with many primates, humans appear to have evolved a remarkable flexibility across the 24-hour cycle — a flexibility that can be adaptive in ancestral contexts and costly when stretched too far by artificial light, shift work, social jet lag, and chronic sleep restriction.
Grateful to Benjamin Taub and IFLScience for covering the work.
Read it here: iflscience.com/fire-may-have…
New conversation in Nautilus: “Where Human Sleep Went Wrong.”
Kristen French and I get into the human sleep paradox, Hadza sleep, circadian function, and why the answer may not be “sleep more” so much as reconnect with the ecology sleep evolved within.
nautil.us/where-human-sleep-…
New episode is live with Dr. Jeremy Koenig on The DNA of Things: “The Human Sleep Paradox.”
We talk Hadza sleep, REM, circadian alignment, and why modern sleep problems may be less about duration than disconnection.
youtu.be/EYd1H7MOdpU?si=1a4L…
Humans are often called a diurnal ape. But that may be too simple.
My new Journal of Human Evolution paper asks whether Homo sapiens is better understood as cathemeral: active across day and night, shaped by firelight, sociality, vigilance, and flexible sleep.
sciencedirect.com/science/ar…
New Rorotoko feature is live: a close-up interview on The Sleepless Ape.
A conversation about ape sleep, human evolution, and why the way we sleep is one of the stranger clues to what made us human.
Read it here: rorotoko.com/micro-interview…
New long-form conversation out on El Podcast: “Everything You Know About Sleep Is Wrong.”
We get into The Sleepless Ape, hunter-gatherer sleep, deep time, and why human sleep is stranger than “we’re doing it wrong.”
Watch here: youtube.com/watch?v=zbyInQyy…
New Rorotoko micro-interview is live: The Sleepless Ape — The wide angle.
This one starts with chimpanzee beds.
Early in my career, I found myself climbing trees in Uganda to measure chimpanzee sleeping platforms — what people often call “nests,” though they are really nightly beds. Chimps build them fresh each evening, selecting particular tree species, weaving branches into stable platforms, and solving a whole suite of sleep problems: safety, thermoregulation, insects, comfort.
That fieldwork changed how I thought about human sleep.
Because at some point in our evolutionary history, our ancestors came down from the trees. We left behind an 18-million-year ape solution to sleep. No more elevated bed. No leafy platform. No arboreal refuge from predators and biting insects.
So the question became: what did humans build instead?
In The Sleepless Ape, I argue that we built a new sleep ecology on the ground: shelter, hearth, environmental preparation, firelight, and social lookouts — what I call the human SHELL. Human sleep did not simply become shorter. It became social, flexible, protected, and astonishingly efficient.
The modern world often imagines good sleep as isolation. But deep in our evolutionary past, sleep was a shared project.
That is part of what made us such weird and beautiful sleepers.
Read the full Rorotoko interview here:
rorotoko.com/micro-interview…
The Wide Awake Ape is on the cover of New Scientist.
This week’s issue features the big idea from The Sleepless Ape: a drastic change in how humans sleep helped propel our species to success.
Humans are the sleepless apes.
newscientist.com/issue/3602/
David Samson retweeted
Co-sleeping isn't just a cultural norm for foragers; it's vital for infant safety, warmth, and feeding. Western advice often oversimplifies, potentially robbing infants of crucial maternal cues and increasing SIDS risk. Full episode: youtu.be/QsrR67hl_Dk @primalprimate