Is it true that humans didn't always sleep for 8 hours every night?

 Yes, it is true that historical and cultural factors have influenced sleep patterns, and the idea of a consistent 8-hour sleep duration is not necessarily universal or fixed throughout human history. The notion of a continuous 8-hour sleep period is a relatively recent development.

Historical records, literature, and anthropological studies suggest that in pre-industrial societies and even up until the 19th century, people often had different sleep patterns compared to contemporary norms. Some historical sleep patterns included:

1. **Biphasic Sleep:**

   - Many historical accounts describe a biphasic sleep pattern, where individuals would have a first sleep period, followed by a waking period in the middle of the night, and then a second sleep period. This wakeful interlude might involve quiet activities or socializing.

2. **Segmented Sleep:**

   - Some societies practiced segmented sleep, where individuals had multiple sleep periods with short periods of wakefulness in between. The night's sleep was divided into two or more distinct segments.

3. **First and Second Sleep:**

   - Historical references, such as in medieval literature, often mention "first sleep" and "second sleep" as natural and accepted parts of the sleep cycle.

4. **Napping:**

   - Napping during the day was a common practice in many cultures, providing an additional period of rest.

The shift toward consolidated, uninterrupted sleep became more pronounced with the advent of industrialization and changes in lifestyle. Factors such as electric lighting, the standardization of work hours, and the influence of societal expectations contributed to the establishment of a more uniform sleep pattern.

In the modern era, the idea of an 8-hour sleep cycle has been popularized as a norm, with recommendations from health authorities advocating for a consistent and adequate duration of sleep for overall well-being. However, it's important to recognize that individual sleep needs can vary, and the idea of a single, universal sleep pattern does not fully capture the diversity of historical and cultural sleep practices. Some contemporary societies still maintain different sleep patterns, and understanding these variations can provide insights into the flexibility and adaptability of human sleep.