I see these claims pop up occasionally and I have found them both very overstated but potentially insightful.

With a perspective that goes farther back in time and a wider geography the sleep patterns promoted here as universal simply stated are not.

However, humans have always been flexible in their sleep patterns, and a lot of modern sleep pattern promotion is overly inflexible.

There are studies of hunter gatherers that lived close to the equator. Most of them did not nap most of the time, but in the summer they might nap during the day 20% of the time. They usually slept 6-7 hours in one stretch. [1]

But sleep was very flexible. In some cultures people would go to sleep at different times so there was always someone around the campfire. Mothers would nurse babies. Some cultures might for example once a month during a full moon stay up and party at night and then nap a lot the next day. And the sleep patterns mentioned in the submitted article show further flexibility.

Your sleep quality is likely a lot lower than a hunter gather due to modern light pollution, ability to use devices and have entertainment at night, and a lot of other factors. Unless you are monitoring your sleep with tracking devices there is a good chance you are probably getting a lot less (like an hour) than you might think. So committing to a 9 hour sleep window is still a good idea even if it might be natural in ideal settings to sleep for just 7 hours. Ultimately though you want to feel well rested with energy for your day rather than satisfying a belief system about sleep.

My approach with young children is to go to bed early so that if I get woken up I can deal with that and have time to go back to sleep. I might end up in the biphasic pattern of northern Europe sometimes with that. There was a time where I more intentionally tried to take a short nap during the day. But now I just take a nap if I feel tired.

References

  * [1] Hunter Gather Sleep study: https://www.cell.com/current-biology/fulltext/S0960-9822(15)01157-4
  * Why We Nap
  * The Old Way
  * Keep the River on Your Right

Solar-based sleep patterns compared to modern norms