The topic of this article interests me, though I must admit that the excessively witty, urban 'style' that is so prevalent in the Atlantic is really annoying to read. Perhaps I'm just cranky from not enough sleep? Or perhaps it's because as I near my sixties I am less physically exhausted at the end of the day. Don't get me wrong; I'm TIRED, but sometimes not muscularly, more mentally fatigued. And on those nights I sometimes wake in the wee hours, so called because that's when you get up to take a wee, right? ;-) Instead of fighting it, I will get up and journal on paper until I start to feel sleepy again, which is typically around dawn. If I use the computer, even with blue-blocker glasses (which I always wear when using any screen) I'll be up for the day and crashing in mid-afternoon. I'd heard of the 'two-sleep' notion from a friend but I didn't find it particularly compelling the way she described it. I thought this article might have more substance, but no.

I DO think that there is an evolutionary explanation for a wide and weird number of human traits and that having certain periods of our lives be prone to not sleeping very long at a time, could have some serious advantages collectively. For virtually all of the history of our species on the planet, and presuming you count Home erectus, that is likely in the neighborhood of 2,000,000 years, all of which time we lived in small, tribal/extended family groups with fire as our greatest technological innovation.

Which brings me to tending the fire and keeping watch for predators/enemies. Teenagers have notoriously weird sleeping habits and are frequently most energized at night, which could be darn handy for a group trying to sleep but needing to keep a fire lit at the cave mouth to keep the lions and hyenas away! And to simply keep the fire going; which was undoubtedly essential for many thousands of years until someone figured out how to start a fire from scratch; just imagine THAT transformation!

Somewhat similarly with the elderly, though we aren't up in the night because of hormones and excess energy, we're just too sore to lay there any longer! Regardless of the cause, the effect of having a few members of the tribe awake at all times to keep the fire burning, was undoubtedly so advantageous to the survival and reproduction of the group that despite possible disadvantages to the individuals, it became a trait or tendency that was ruthlessly selected for.

So, David, your comment about tending the fire and changing the guard was, I think, absolutely right on.

Well, I did not even skim over the article, but searched on every term I could think of relative to breast feeding an infant. An article that talks about evolutionary sleep habits without addressing how a woman's sleep is interrupted every single night, multiple times, just to keep alive a new generation is missing a big chunk.

Every woman who nursed her children will have stories of sleep deprivation. I'll only say that it was for several months that I had to awaken every two hours to nurse, and that took forty minutes. That means I got sleep in 1 hour, 20 minute episodes. Dear god!-- if I had to stoke the fire or finish daytime chores during the night as well!