Humans have evolved to sleep in a monophasic sleep pattern, which means sleeping once per 24-hour cycle. However, some argue that biphasic sleep, which involves sleeping in two segments per day, may be more in line with our natural circadian rhythms.
The Evolution of Monophasic Sleep
For most of human history, biphasic sleep was the norm. Humans would tend to sleep in two segments, with a period of wakefulness in between. The first sleep period began around dusk and lasted for 3-4 hours. Then people would wake up for 1-2 hours before going to sleep again until dawn.
This pattern emerges because of our natural circadian rhythms. The hormone melatonin rises in the evening, inducing sleepiness. In the early morning hours, melatonin levels drop while cortisol rises, causing us to wake up.
With the advent of artificial lighting, humans began condensing their sleep into one continuous block at night. Work schedules and social demands also reinforce monophasic sleep. This monophasic pattern is now dominant in modern industrialized societies.
The Case for Biphasic Sleep
Proponents of biphasic sleep argue that two sleep periods better align with our natural circadian rhythms and may provide health benefits:
- The afternoon nap aligns with the post-lunch dip in alertness and performance.
- Splitting sleep may enhance creativity and problem-solving.
- Napping may improve alertness and performance.
- Biphasic sleep allows greater light exposure in the morning and evening.
- Disruptions at night are less detrimental if daytime naps can compensate.
Some studies do show cognitive and health benefits to biphasic sleep. Performance and alertness increase after a short nap. Blood pressure drops after a midday nap.
Challenges of Biphasic Sleep
While biphasic sleep may seem intriguing, adopting this pattern in modern society presents difficulties:
- Most work schedules are not compatible with a daytime nap period.
- People may not be able to fall asleep for a nap due to mid-afternoon troughs in melatonin levels.
- Biphasic sleep requires strict timing of sleep periods.
- Too much daytime sleep can adversely affect nighttime sleep quality.
- Social norms dictate sleeping mainly at night.
Biphasic sleep is most practical for situations like shift work or jet lag, where circadian rhythms are already disrupted. The majority of people conform to monophasic sleep for functionality.
Individual Variation in Sleep Patterns
There is tremendous individual variability in sleep needs and patterns. Some people thrive on less sleep, while others require more. Genetics, age, medications, and health conditions also influence sleep. Some people function well on polyphasic sleep cycles with multiple naps.
In certain cases like insomnia or sleep disorders, biphasic sleep may help. People who struggle to get continuous nighttime sleep can try splitting sleep into two periods. For others, biphasic sleep may hinder sleep consolidation at night.
Ultimately, there is no single “right” way to sleep. Each person must determine their optimal sleep pattern based on their circadian rhythms, lifestyle factors, and individual needs.
Conclusion
Humans are biologically adapted for biphasic sleep, with circadian dips and rises in sleep drive across the 24-hour cycle. Modern society favors monophasic sleep for practical reasons. While we have evolved from our biphasic ancestral sleep patterns, biphasic sleep remains beneficial for some individuals. There is no universal optimal sleep pattern. Individuals must determine the sleep cycle that allows them to feel rested and function at their best.