It'll likely be the nth time Matthew Walker is cited here, but in his interview with Joe Rogan, he mentions this is likely a societal trend rather than a biological need:
> Joe Rogan: Yeah, I've heard this recently, that people - that you should have two sleeps. The idea of two sleeps.
> Matthew Walker: Yeah, it's actually a little different than the idea of two sleeps. So there was a time in the sort of Dickensian era where people would sleep for the first half of the night, maybe sort of 4 hours or so. Then they would wake up, they would socialize, they would eat, they would make love, then they would go back and have a second sleep. If you look at natural biological rhythms in the brain and the body, that doesn't really seem to be how we were designed. It certainly seems to be something that we did in society, but I think it's more of a societal trend than it was a biological edict. However, we do seem to have two sleep periods. Those tribes will often sleep about 6.5, 7 hours of sleep at night. And then especially in the summer they'll have that siesta like behavior in the afternoon. And all of us have that, sort of this - what's called the post-prandial dip in alertness, just means "after lunch" - and if I measure your brainwave activity with electrodes, I can see a drop in your physiological alertness somewhere between 2 to 4 pm in the afternoon [irrespective of diet].
https://www.youtube.com/watch?v=pwaWilO_Pig&t=3294
> Joe Rogan: Yeah, I've heard this recently, that people - that you should have two sleeps. The idea of two sleeps.
> Matthew Walker: Yeah, it's actually a little different than the idea of two sleeps. So there was a time in the sort of Dickensian era where people would sleep for the first half of the night, maybe sort of 4 hours or so. Then they would wake up, they would socialize, they would eat, they would make love, then they would go back and have a second sleep. If you look at natural biological rhythms in the brain and the body, that doesn't really seem to be how we were designed. It certainly seems to be something that we did in society, but I think it's more of a societal trend than it was a biological edict. However, we do seem to have two sleep periods. Those tribes will often sleep about 6.5, 7 hours of sleep at night. And then especially in the summer they'll have that siesta like behavior in the afternoon. And all of us have that, sort of this - what's called the post-prandial dip in alertness, just means "after lunch" - and if I measure your brainwave activity with electrodes, I can see a drop in your physiological alertness somewhere between 2 to 4 pm in the afternoon [irrespective of diet].