[GrumpyGoblin]

> based on the brain scans of nearly 4,000 people aged under one to 90, mapped neural connections and how they evolve during our lives.

That is an absurdly small sample size to make such a conclusion.

It seems this age range could at least partly be culturally attributed. In modern industrialized life, many people don't have to "grow up" until a later age. At the risk of generalizing, people have more support from family, friends, and society at large.

Is the forming of those neurons based on some natural law, or is that people just haven't had to live the experiences that do so until their 30's nowadays?

As far as I know, forming neurons isn't something that "just happens". It happens due to catalysts in life. In pre-modern society, and indeed most likely in under-industrialized nations today, those catalysts, those experiences, would happen earlier. As others mentioned, there is a clear correlation with the typical age in which modern society gets married, settles down, and has kids.

I wonder what that era age would have been 200+ years ago.

[GeoAtreides]

>That is an absurdly small sample size to make such a conclusion.

Please show the statistical calculations in support of such assertion.

[GrumpyGoblin]

You require "statistical calculations" to support the notion that a sample size of 4000 people in two countries, two of the most modernized and affluent nations on the planet at that, is too small for a study to conclude how the human brain works across billions of people alive today across the world, Much less in human history? How about common sense?

Ok, let's do some math.

Approximately 108 to 117 billion humans are estimated to have lived in human history. Let's take 110 billion (the low end) for our purposes.

4,000 / 110,000,000,000 = 0.000003636%

Let's just go with people living today, which is approximately 8 billion (the low end).

4000 / 8 billion = 0.00005%

Not sure if that covers the "statistical" part of your requirement, but it covers the "calculations" part.

I myself would be hesitant to make claims about knowing how neurons and brains and ages work based on a sample size of pessimistically 0.000003636% or even optimistically 0.00005% of the human population and their brains.

[GeoAtreides]

oh man, prepare to have your mind blown:

https://en.wikipedia.org/wiki/Sample_size_determination

Sample size is a whole chapter in statistics, and it's surprisingly how small the sample can be (if certain conditions are present)

[AHatLikeThat]

Not sure why this is downvoted. The authors themselves note that parenthood could be a catalyst for the change at 30-- in previous centuries, when parenthood happened much earlier, why could it not affect the brain's timeline? This study is simply descriptive of a particular dataset, a collection of snapshots at a particular time and place. Certainly the brain is elastic and responsive to external conditions.

What I noticed is that the 4000 samples are all from England and the U.S. Replicating this study with a greater geographical and socio-cultural diversity would be very useful in supporting or expanding these results.