Comment by dredmorbius | Hacker News Reader

Comment by dredmorbius | Hacker News Reader

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That depends very much on overall birth and death rates, though to a first approximation: half. And half the people alive when you first began would die before you'd completed your meetings.

I've played with the concept a few different ways, some variants:

* Count only your waking, working hours -- roughly 1/3 of your life.

* Take a lifespan and divide it either by people met, or time per person, to find the other.

* Dunbar's Number, 150, divided over 60 years, works out to 146 days per person. If we look at a more historically accurate lifespan of 40 years, that's closer to 100 days experience per person, in a pre-modern tribe or village.

* You can look at training or education and life -- how many effective careers can a person have if they must undergo a college-equivalent retraining between each? A working life of 40 years divided by 4 years gives an upper bound of 10 retrainings. Either we have fewer retrainings, or shorter ones, or both, if we need greater flexibility.

* The power of combined communications, and their limitations. Conversations are two-way, and rarely scale beyond 4-5 participants. Broadcast messaging, starting with lectures, are efficient, but at the cost of interactivity and accomodation betweeen speaker(s) and listener(s).

* The multiplicative power of mass media. The same message reaching hundreds, thousands, millions, or billions of souls. Most of the most highly-repeated messages are propaganda, in the original or contemporary sense, or both.

* Time vs. repetition. Some messages become widely spread, but briefly (say, Gangnam Style, played over 2 billion times). Some have been part of cultural lore for tens of thousands of years, see Idres Shah's collection World Tales for numerous examples. What does it mean for a narrative to be truly embedded in a culture, or multiple cultures?

Another element is looking at the different dynamics of information poor vs. information rich environments. I'm starting to think that a healthy function in one is pathological in the other, and vice versa. This doesn't seem widely recognised.

The 40 year lifespan caught my eye because for a long time I’d always had this idea that in our near past old people were rare. I recently learnt that in historic context that it’s skewed by a lot of infant mortality.

So if you lived over 2 years old you were probably likely to live to be a lot older than 40.

I’ll try and find a source, but at the moment I can’t remember where I read this.

Generally correct -- life expectency at birth was pretty poor, but at 5, 10, 20, ... looked increasingly more comparable to modern expectancies, at least relatively. There are numerous credible records of ancients from Greece & Rome living to their 60s or 70s, at least. In more primitive cultures, not so much. And women still faced immense risks through pregnancy & childbirth.

This makes me think that much of longevity is based both on establishing a good start (nutrition, health, and conditions during gestation, infancy, and childhood), and then generally on avoiding accidents, risks, and mishaps (exposure to disease, violence, injury) afterwards. Modern epidemiological and public health records somewhat bear this out, as a New York City Department of Public Health graph, "The Conquest of Pestilence", showing decreased mortality 1800 - 2000 (or 2015, in some versions) makes clear:

https://thesocietypages.org/graphicsociology/2010/06/22/conq...

What's most interesting is how little impact "modern medicine" -- all increases since 1920 -- has provided. Though yes, by 1920 we did have germ theory of disease, and a basic understanding of nutrition.

And yes, the chart shows overall mortality, not life expectancy (through these are related). I'd like to see the latter for the same period.

I have run across several plots of life expectancy for the latter half of the 20th century. These show that most increase has not come from increasing top-end expectancy (though this has increased somewhat -- say, for white women), but by raising the life expectancy of disadvantaged populations -- the shifts for black and other nonwhite men and women have been far greater than for white men and women, in the US, for example, since 1960 and 1970. Again arguing that addressing the basics of healthcare access, hygiene, and risk avoidance offers the greatest benefits.

The mid-1850s peak suggests that modern cities, prior to notions of public health (the date of the NYC dept's formation is indicated, about 1860) were significantly worse than a more rural setting, from a health perspective. Ancient histories tend to support this notion, and there are books such as Kyle Harper's The Fate of Rome which explore the co-evolution of the Roman Empire and the diseases and plauges which, er, diseased and plagued it, with the formation of cities, trade routes, and exchange and incubation of disease vectors and agents via these.

Another thought is that the lifting of infancy / early childhood mortality represents a tremendous reduction in selective pressure on human populations, implications of which have not yet become clear. Though the possiblity that this is not entirely positive to humans occurs.

The other thought that's occurred is that this decrease in mortality indicates a

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