Nature rarely moves in a straight line. Day becomes night, winter gives way to spring, plants germinate, grow, flower, seed, decline and return to the soil, and tides rise and fall. Activity is followed by rest.
Yet modern life often asks something quite different of us: consistency. The same alarm; the same working hours; the same expected productivity. All the while artificial light stretches the day long beyond sunset, while electricity, screens and climate-controlled buildings increasingly insulate us from the rhythms outside (although I’m grateful for climate-control during winters in Cape Town).
But a living body is not a machine designed to produce the same output at every hour of every day – it is rhythmic.
Nature Keeps Time
Plants are not simply responding passively to sunrise and sunset. They possess internal circadian clocks that anticipate daily changes in their environment. These clocks influence photosynthesis, metabolism, growth and other processes, while seasonal changes in day length help regulate events such as flowering (1,2).
Humans also possess biological clocks. Our circadian system produces rhythms of approximately 24 hours and helps coordinate sleep and wakefulness, hormone secretion, metabolism, body temperature and many other physiological functions. Rather than one clock controlling everything, clocks exist throughout the body and communicate with one another, with a central timing system in the brain helping synchronise them (3).
Light is one of the strongest environmental signals setting this system.
This is why morning and evening are biologically different experiences – not simply different numbers on a clock.
We Were Never Designed for Constant Daylight
For most of human history, bright light meant daytime and darkness meant night. Modern artificial lighting has changed that relationship dramatically.
Light reaching the eyes in the evening and at night can shift or disrupt circadian timing, although the effect varies with its intensity, timing, duration and wavelength (4). Research into the long-term health consequences of artificial light at night is continuing, and some proposed effects remain less certain than popular discussions sometimes suggest.
The broader principle, however, is well established:
Our biology pays attention to when things happen.
Sleeping at midnight is not necessarily biologically identical to sleeping at midday. Eating, exercising and receiving light at different times can interact differently with our internal clocks. Timing matters.
There Is a Time for Growth… and a Time for Rest
One of the lessons I find particularly valuable in nature is that growth is never continuous. A tree does not apologise for winter. A seed does not fail because it has not yet germinated.
Rest, dormancy and decline are not interruptions to nature’s productivity. They are part of its cycle. I think we often forget this when thinking about ourselves. We expect energy to remain constant despite illness, emotional difficulty, poor sleep, demanding work or changing circumstances. Tiredness becomes something to overcome and rest becomes something we must earn.
But perhaps the better question is: What season is this person in right now?
There are periods in life suited to building, learning, creating and expanding. There are also periods for recovery, consolidation, grieving, withdrawing and simply maintaining what already exists. Neither is inherently better. A cycle requires both.
Rhythms Within Rhythms
Human physiology contains many overlapping rhythms. The sleep–wake cycle is perhaps the most obvious, but hormones, immune activity, metabolism and gene expression also change across the day (3,5).
Sleep itself is intertwined with circadian timing rather than being merely a period when the body “switches off”. Sleep pressure and circadian rhythms interact continuously to influence when we become sleepy, when we wake, and aspects of physiological recovery (5).
These daily cycles then sit within larger ones: stages of life, reproductive cycles, changing seasons and the inevitable movement between activity and rest. We live within rhythms inside rhythms.
Cyclical Rhythms in Traditional Western Herbal Medicine
For me, this principle changes an important question in herbal practice. Instead of asking only what support a person needs, we should sometimes ask when it is needed: When is their energy strongest? When do symptoms worsen? How do they sleep? What happens before those symptoms appear? Has their routine become disconnected from daylight, regular meals or adequate periods of rest? Are we supporting activity when the body is asking for recovery?
Herbs can form part of that support, but they do not exist outside time either.
A stimulating herb in the evening and the same herb in the morning are not necessarily the same intervention in practice. Likewise, relaxing herbs, meals, exercise, rest and light all occur within a biological day.
Traditional practice therefore encourages observation. Not every variation requires correction. Sometimes the body is not malfunctioning – sometimes it is just cycling.
Returning to Rhythm
Cyclical Rhythms does not mean rejecting modern life and attempting to live according to some imagined prehistoric schedule. It means remembering that beneath our calendars, deadlines and electric lights, an older clock is still ticking. We are organisms living on a rotating planet where light becomes darkness, and activity requires rest. Growth gives way to decline, and decline creates the conditions from which new growth eventually becomes possible.
Perhaps health is not about remaining permanently at our peak. Perhaps it is partly about learning to recognise the season we are in – and allowing ourselves to move through it.
Nature does not demand sameness. It asks us to participate in time.
References
- Mortada, M., Xiong, L. & Mas, P. “Dissecting the Complexity of Local and Systemic Circadian Communication in Plants.” npj Biological Timing and Sleep 1, 1 (2024). DOI: 10.1038/s44323-024-00003-3.
- Wang, F., Han, T. & Chen, Z.J. “Circadian and Photoperiodic Regulation of the Vegetative to Reproductive Transition in Plants.” Communications Biology 7, 579 (2024). DOI: 10.1038/s42003-024-06275-6.
- Mortimer, T. et al. “Circadian Clock Communication During Homeostasis and Ageing.” Nature Reviews Molecular Cell Biology 26, 314–331 (2025). DOI: 10.1038/s41580-024-00802-3.
- Mendoza, J. “Circadian Disruptions and Brain Clock Dysregulation in Mood Disorders.” Nature Mental Health 2, 749–763 (2024).
- Franken, P. & Dijk, D.-J. “Sleep and Circadian Rhythmicity as Entangled Processes Serving Homeostasis.” Nature Reviews Neuroscience 25, 43–59 (2024). DOI: 10.1038/s41583-023-00764-z.