Updated: August 2026
In 2017, three scientists received the Nobel Prize in Physiology or Medicine for discoveries that helped explain one of the most familiar but surprisingly complex features of life: why our bodies operate on an approximately 24-hour biological clock.
Jeffrey C. Hall, Michael Rosbash and Michael W. Young were jointly awarded the 2017 Nobel Prize in Physiology or Medicine for their discoveries of the molecular mechanisms controlling circadian rhythm.
Their research helped scientists understand how genes and proteins inside cells create a biological timing system that allows humans and other organisms to anticipate and adapt to the regular cycle of day and night.
The discovery goes far beyond explaining when we become sleepy.
Circadian rhythms influence sleep, hormone release, body temperature, metabolism, eating behaviour and many other physiological processes.
What Is Circadian Rhythm?
A circadian rhythm is a natural biological cycle that operates over approximately 24 hours.
Humans, animals, plants and even many microorganisms have biological processes that change according to the time of day.
In humans, the most obvious example is the sleep-wake cycle.
You are normally more alert during certain parts of the day and become sleepy at other times. But sleep is only one part of the system.
Circadian rhythms also influence:
Body temperature
Hormone levels
Metabolism
Blood pressure
Eating patterns
Alertness
Behaviour
Sleep timing
Light and darkness are particularly important signals for synchronising these rhythms with the external environment.
The National Institute of General Medical Sciences explains that almost every tissue and organ in the human body has its own circadian rhythm, with these rhythms coordinated with the daily cycle of day and night.
Who Won the 2017 Nobel Prize in Medicine?
The Nobel Prize in Physiology or Medicine 2017 was awarded jointly to:
Jeffrey C. Hall
Jeffrey C. Hall is an American geneticist whose research helped reveal the genetic and molecular mechanisms controlling biological rhythms.
Michael Rosbash
Michael Rosbash is an American geneticist and chronobiologist whose work with Hall contributed greatly to understanding how clock genes generate approximately 24-hour biological rhythms.
Michael W. Young
Michael W. Young is an American geneticist whose discoveries of additional clock genes helped explain how the molecular biological clock maintains its timing.
Each scientist received one-third of the Nobel Prize.
The Nobel Assembly awarded them the prize specifically “for their discoveries of molecular mechanisms controlling the circadian rhythm.”
What Did Hall, Rosbash and Young Discover?
Scientists had known long before 2017 that living organisms possess internal biological rhythms.
The major unanswered question was:
How does the biological clock actually work inside a cell?
Hall, Rosbash and Young helped provide the molecular explanation.
Much of their Nobel-winning research used the fruit fly Drosophila melanogaster.
Fruit flies might appear very different from humans, but they have proved enormously useful for understanding genetics and fundamental biological processes.
The researchers studied genes involved in controlling the flies' daily rhythms and discovered a remarkable feedback system.
The Period Gene and PER Protein
An important breakthrough involved a gene known as period.
Earlier research had already linked mutations in the period gene with abnormal daily rhythms in fruit flies.
Hall and Rosbash, working together, and Young independently isolated and characterised the period gene during the 1980s.
The researchers subsequently demonstrated how the gene participates in a molecular feedback system.
The period gene produces a protein called PER.
PER accumulates in cells during the night and is broken down during the day.
As PER accumulates, it eventually helps suppress the activity of the gene responsible for producing it.
When PER levels subsequently fall, the gene becomes active again.
This creates a repeating molecular feedback loop.
In simplified terms:
period gene activated → PER protein produced → PER accumulates → period gene activity is inhibited → PER declines → gene becomes active again.
This cycle contributes to the approximately 24-hour rhythm of the biological clock.
Michael Young and the Timeless Gene
There was still an important problem with the emerging explanation.
PER needed to enter the cell nucleus to influence the activity of the period gene.
How did that happen?
In 1994, Michael Young discovered another clock gene called timeless.
This gene produces the TIM protein.
When TIM binds with PER, the proteins can enter the cell nucleus and contribute to blocking period gene activity.
This helped explain an important missing part of the biological feedback loop.
The Doubletime Gene
Young subsequently identified another gene called doubletime.
The protein produced by this gene helps delay the accumulation of PER.
That delay contributes to adjusting the biological cycle so that it more closely corresponds to approximately 24 hours.
Together, these discoveries helped scientists understand that the biological clock is not simply an abstract response to sunrise and sunset.
It is supported by an intricate molecular system operating inside cells.
Why Was This Discovery Important Enough for a Nobel Prize?
Life on Earth has evolved in an environment where light and darkness change predictably because of the Earth's rotation.
Organisms therefore benefit from being able to anticipate those changes rather than simply reacting after they happen.
The biological clock helps coordinate physiology and behaviour with different phases of the day.
The work of Hall, Rosbash and Young revealed fundamental mechanisms behind that timing system.
Their discoveries also established principles that extend beyond fruit flies.
Similar biological-clock mechanisms operate in other animals, plants and humans.
That transformed scientists' understanding of how genes can create self-sustaining biological rhythms.
What Does the Biological Clock Control in Humans?
Circadian timing affects many processes in the human body.
Sleep and Wakefulness
The sleep-wake cycle is probably the most familiar circadian rhythm.
The biological clock helps determine when the body is prepared for wakefulness and when it is prepared for sleep.
This is one reason maintaining dramatically different sleep times from day to day can feel difficult.
Hormone Release
Several hormones follow daily patterns.
Their concentrations can rise or fall at characteristic times, helping coordinate physiological processes with the body's expected periods of activity and rest.
Body Temperature
Core body temperature changes throughout the day rather than remaining perfectly constant.
These variations are influenced partly by circadian timing.
Metabolism
Circadian systems interact with metabolism and the timing of food intake.
The body does not necessarily process every physiological activity identically at every hour of the day.
Blood Pressure
Blood pressure also follows daily patterns influenced by sleep, activity and biological timing.
What Happens When Circadian Rhythms Are Disrupted?
The biological clock can become temporarily misaligned with the external environment or a person's behaviour.
Two familiar examples are jet lag and shift work.
Jet Lag
Suppose someone travels rapidly from Nigeria to a country several time zones away.
The local clock may say it is morning, but the traveller's internal biological system may still be operating according to the previous time zone.
The body needs time to adjust.
This mismatch can produce:
Daytime sleepiness
Difficulty sleeping at the appropriate local time
Reduced concentration
Poor coordination
General fatigue
This is jet lag.
The existence of jet lag provides an everyday demonstration that the body cannot instantly reset its internal timing simply because a person changes the clock on a phone.
Shift Work
People who regularly work at night may need to remain awake and active during a period when their biological system would normally promote sleep.
They may then try to sleep during daylight hours when environmental signals promote wakefulness.
This can create repeated circadian disruption, particularly when work schedules frequently change.
Does Using a Phone at Night Affect Your Biological Clock?
Light is one of the most important environmental signals affecting circadian timing.
Exposure to light during the evening and night can influence biological clocks.
Electronic devices are therefore relevant, especially when bright screens contribute to prolonged nighttime light exposure and delayed sleep.
However, phones should not be presented as the sole cause of sleep problems.
Sleep can be affected by many factors, including:
Work schedules
Stress
Caffeine
Medical conditions
Medicines
Noise
Environmental light
Irregular sleep schedules
Mental health conditions
Reducing unnecessary bright light and screen exposure close to bedtime can form part of healthier sleep habits, but persistent sleep problems may require proper assessment.
Is Circadian Rhythm the Same as Sleep?
No.
Sleep and circadian rhythm are closely connected, but they are not identical.
Circadian rhythm describes approximately 24-hour biological cycles affecting many functions.
Sleep is one of the processes influenced by those rhythms.
This distinction matters because the biological clock affects far more than whether someone feels tired.
What Is Chronobiology?
Chronobiology is the scientific study of biological rhythms and how biological processes change with time.
Circadian biology is an important part of this field.
Research now examines questions such as:
How sleep timing affects health
How shift work affects physiology
How light changes biological timing
How circadian rhythms interact with metabolism
How ageing affects biological clocks
Whether the timing of medicines influences their effects
How circadian disruption interacts with disease
The Nobel-winning discoveries helped provide a molecular foundation for this much broader research field.
Can Circadian Disruption Affect Health?
Short-term disruption can clearly affect alertness, concentration, coordination and sleep.
Long-term circadian disruption and chronic sleep loss have also been associated with increased risks of several health problems.
Research continues into relationships involving:
Obesity
Diabetes
High blood pressure
Cardiovascular health
Mood disorders
Metabolic disorders
Some cancers
Neurological conditions
Association does not mean that an irregular night's sleep directly causes these diseases.
Human health is influenced by genetics, behaviour, environment, occupation and many other factors.
The important point is that biological timing is now recognised as an important component of physiology and health.
Circadian Rhythm and Mental Performance
Circadian rhythms also influence alertness and cognitive performance.
When the internal biological clock is poorly aligned with required activity, people may experience:
Drowsiness
Difficulty concentrating
Slower reactions
Reduced coordination
Problems maintaining attention
This becomes particularly important in occupations involving driving, machinery, healthcare, aviation and other safety-sensitive activities.
Why Were Fruit Flies Used?
One of the most interesting aspects of the Nobel-winning research is that much of it was performed using fruit flies.
Scientists use model organisms because many fundamental biological mechanisms have been conserved through evolution.
Fruit flies:
Reproduce quickly
Are relatively easy to study
Have well-characterised genetics
Allow researchers to study gene mutations
Share important biological mechanisms with more complex organisms
Discoveries made in fruit flies can therefore reveal principles that scientists can subsequently investigate in humans and other organisms.
This is a powerful example of why basic biological research matters.
Research that initially appears far removed from everyday human health can uncover fundamental mechanisms relevant across species.
Was the Biological Clock Discovered in 2017?
No.
The 2017 Nobel Prize did not mean Hall, Rosbash and Young suddenly discovered that humans have daily biological rhythms.
Scientists had observed biological rhythms for centuries.
One famous early experiment occurred in 1729, when French astronomer Jean-Jacques d'Ortous de Mairan studied a plant whose leaves opened during the day and closed at night.
When the plant was placed in continuous darkness, its leaves continued following a daily rhythm.
This suggested that the rhythm was generated internally rather than being merely an immediate reaction to sunlight.
Much later, genetic research began revealing the machinery responsible for these rhythms.
In 1971, researchers Seymour Benzer and Ronald Konopka identified fruit-fly mutations that altered normal daily behavioural rhythms.
Hall, Rosbash and Young subsequently helped uncover the molecular machinery behind this biological clock.
The Nobel Prize recognised those molecular discoveries.
When Was the 2017 Nobel Prize Announced?
The Nobel Assembly at Karolinska Institutet announced the Nobel Prize in Physiology or Medicine on 2 October 2017.
Jeffrey C. Hall, Michael Rosbash and Michael W. Young shared the prize equally.
The prize amount in 2017 was 9 million Swedish kronor, divided among the three laureates.
But the lasting significance of the award was not the prize money.
It was recognition of research that fundamentally changed our understanding of how living organisms keep biological time.
Frequently Asked Questions
Who won the 2017 Nobel Prize in Physiology or Medicine?
Jeffrey C. Hall, Michael Rosbash and Michael W. Young jointly received the award.
Why did Hall, Rosbash and Young win the Nobel Prize?
They were recognised for discoveries explaining molecular mechanisms that control circadian rhythm.
What is a circadian rhythm?
A circadian rhythm is an approximately 24-hour biological cycle affecting processes such as sleep, hormone release, body temperature, metabolism and behaviour.
What is the body's biological clock?
The term refers to biological timing systems that help coordinate physiological processes with regular environmental cycles, particularly day and night.
What gene did the Nobel laureates study?
An important part of their research involved the period gene and its PER protein. Their work also helped reveal additional clock components, including timeless and doubletime.
Why were fruit flies important?
Fruit flies allowed researchers to manipulate and study genes involved in daily biological rhythms. The fundamental principles discovered through these experiments proved relevant to biological clocks in other organisms.
Does circadian rhythm only control sleep?
No. Circadian timing influences numerous processes, including hormones, metabolism, body temperature, behaviour and blood pressure.
What causes jet lag?
Jet lag occurs when the body's internal biological timing remains temporarily aligned with the previous time zone after rapid travel across multiple time zones.
Can night-shift work disrupt circadian rhythm?
Yes. Night work can create a mismatch between working and sleeping schedules and the body's normal responses to environmental light and darkness.
Why the 2017 Nobel Prize Still Matters
The 2017 Nobel Prize tells a larger story about scientific discovery.
Hall, Rosbash and Young did not simply identify another gene.
Their research helped reveal a fundamental mechanism through which living organisms measure biological time.
It helped explain why our bodies anticipate day and night, why jet lag exists, why sleep timing matters and why physiological processes change according to the time of day.
Their work also demonstrates the importance of basic science.
Experiments involving tiny fruit flies eventually helped scientists better understand a biological system operating throughout the human body.
Nearly a decade after the Nobel Prize was awarded, circadian biology remains an active field of research with implications for sleep, metabolism, neurological health, shift work and the timing of medical treatment.
The question that inspired the research remains remarkably simple:
How does the body know what time it is?
The discoveries recognised by the 2017 Nobel Prize gave science a major part of the answer.
Key Takeaways
Jeffrey C. Hall, Michael Rosbash and Michael W. Young won the 2017 Nobel Prize in Physiology or Medicine for discoveries of molecular mechanisms controlling circadian rhythm.
Their experiments with fruit flies helped explain how genes and proteins create an approximately 24-hour biological feedback system.
Circadian rhythms influence much more than sleep. They are involved in hormone release, metabolism, body temperature, blood pressure and behaviour.
The biological clock can become temporarily misaligned during jet lag and can be repeatedly disrupted by circumstances such as night-shift work.
Their discoveries transformed circadian biology and helped establish an important foundation for continuing research into biological timing and human health.
References and Further Reading
Nobel Prize. The Nobel Prize in Physiology or Medicine 2017.
Official Nobel Prize 2017 overview
Nobel Prize. The 2017 Nobel Prize in Physiology or Medicine: Discoveries of Molecular Mechanisms Controlling the Circadian Rhythm.
Scientific background to the Nobel-winning discoveries
Nobel Prize. 2017 Nobel Prize in Physiology or Medicine Press Release.
Official Nobel Prize press release
National Institute of General Medical Sciences. Circadian Rhythms.
NIGMS guide to circadian rhythms
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