Human beings are shaped by their habits and heritage. In the era before alarm clocks, the start of a new day was heralded by the crowing of roosters, ushering in the morning with a natural wake-up call. Farmers would rise with the sun, tending to their fields, milking cows, and settling down for the night as daylight waned. In those times, there was no electricity, and the cycles of life were closely intertwined with the rhythm of day and night.
Fast forward to the modern lifestyle, and we find a stark contrast to those bygone days. Nowadays, many of us are jolted awake not by the soothing sounds of nature but by the shrill beeping of alarm clocks or the buzz of clock radios. Getting out of bed can be a struggle, and we often resort to hitting the "snooze" button, craving just a few extra moments of precious sleep. Heavy drapes on our windows block out the early rays of sunlight, keeping us shielded from nature's daily spectacle. In the evenings, the pull of late-night TV shows can keep us awake until the wee hours of the night, often past our body's natural bedtime.
Our predicament arises from the fact that our bodies require a certain amount of sleep. Studies on animals reveal that they have well-defined daily patterns, intricately linked to the changing seasons. In the autumn, as many plants and animals prepare for the impending winter, they undergo adjustments in their activities. Food becomes scarcer, and the birds fly south for warmer climes. During this period, they tend to eat less since there's less sustenance available. However, as spring renews the world, nature awakens with vigor. Birds return from their migrations, and trees sprout fresh foliage.
Most animal species synchronize their life events with the seasons, ensuring that crucial functions are carried out when resources are abundant. For example, lambs are born in the spring when their mothers can find ample food to nurse their offspring. In the tropical rainforests, birds time their breeding to coincide with the dry season. In the Arctic, reproduction is synced with the melting of snow and ice.
But how do animals predict these seasons in advance? Temperature fluctuations cannot be the sole answer, as there are occasional "Indian Summers" in the fall, yet the birds continue their natural cycles. It turns out that the most significant factor is the presence of daylight, more specifically, the day-night cycle. Animals and plants detect changes in the length of days and nights, perceiving the coming of winter in the fall and the arrival of spring in the lengthening days. This photoperiod, or day-length, plays a pivotal role in guiding the timing of events in their lives. This phenomenon is well-known to horticulturists who manipulate photoperiod to induce flowering in plants like poinsettias for the Christmas season and daylilies for Easter.
Humans, too, are profoundly affected by light. The natural rhythms of our sleep and wake cycles are regulated by light. In both animals and humans, the hormone melatonin is instrumental in the initiation of sleep. Melatonin is produced by the pineal gland, a tiny structure in the brain. In the evening, the pineal gland responds to diminishing daylight by initiating melatonin production. This hormone is released into the bloodstream, inducing drowsiness. Melatonin secretion peaks in the middle of the night, during our deepest sleep. As morning arrives, bright light entering the eyes signals the pineal gland to halt melatonin production, effectively rousing us from sleep.
The pineal gland is intricately linked with the broader hormonal system, influencing the functioning of other bodily systems. During the dark hours of sleep, melatonin modulates the release of hormones from vital organs like the pituitary gland, which serves as the master regulator of the hormonal system. The pituitary gland, in turn, oversees the secretion of hormones controlling growth, milk production, egg and sperm production. It also governs the thyroid gland, responsible for metabolism, and the adrenal glands, which manage waste elimination in the body. The fluctuations in light and darkness that vary seasonally can profoundly impact growth, reproduction, and activity patterns in animals and, indeed, humans.
Surprisingly, even in our modern lives and the prevalence of "enclosed structures," our bodies continue to respond to external factors and seasonal variations. Research has shown that children's growth rates are influenced by the seasons. Studies conducted in Germany, Sweden, and Scotland reveal that height and weight gains are most pronounced in the spring and early summer. In many countries, the highest rates of conception occur in the summer, when daylight hours are longest. Seasons have been observed to influence the timing and duration of sleep, pain sensitivity, alertness, eating habits, mood, the onset of menstruation in women, and sexual activity.