Summary:
- For centuries, humans followed a "biphasic sleep" pattern, where they slept in two segments during the night with a period of wakefulness in between.
- The introduction of electricity and artificial lighting in the 19th century disrupted this natural sleep cycle, leading to the modern "monophasic sleep" pattern of a single continuous sleep period.
- The change in sleep patterns has had significant impacts on human health and behavior, with potential implications for our understanding of circadian rhythms and the importance of natural light-dark cycles.