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Comment by tjpnz | Hacker News Reader

Why do I keep (mis)remembering a fact that most members of the human race are alive right now?

Same thing -- I know I came across that at some point in the past few years, and it seemed reasonable enough given exponential growth that I just accepted it as true without researching it further.

Turns out it's one of those totally wrong "factoids" that nevertheless keeps getting repeated (like the only man-made structure you can see from space being the Great Wall, etc.), and which dates as far back as the 1970's according to Scientific American: https://www.scientificamerican.com/article/fact-or-fiction-l...

This is worth a read for those unfamiliar with this argument. Essentially, it’s a way to make a probabilistic guess for when humans will go extinct based on the number of humans that have been born. There are several variants and as far as I know, the argument’s premise has never been conclusively refuted.

I think the biggest problem with this utter nonsense is this:

> In other words, one can assume with 95% certainty that any individual human would be within the last 95% of all the humans ever to be born

"any individual human" really means "a human chosen at random" from all humans who will ever live. Then they go on to assume that this is representative of the humans who have already lived. But clearly there's a problem there. They find a statistic that is true of all past-and-future humans and then assumed it must be equally true of all past humans as well. In fact we've exactly chosen the subset (past humans) as those that are least likely for this statistic to apply. It'd be like deriving some statistic about being 95% sure any given human can run a mile within 10 minutes, and then applying that statistic specifically to those humans with no legs. It's that dumb -- clearly past humans are fundamentally different from past-and-future humans in exactly the property they're sampling.

You can easily see this problem by simply going back in time and applying the same argument at any point in history. At some point, the total number of humans who had ever been born was 1 billion. At that point, we would have been 95% sure that the total number of humans would never exceed 20 billion. Oops! In fact, we would have been 99% sure that the total number of humans would never exceed 100 billion. Double oops!

Go back to when the total number of humans who had ever been born was 1 million. We would have been 99.999% sure the total number of humans would never exceed 100 billion. Triple oops!

It's a nonsense argument.

There are a number of counter arguments that I don’t see represented in this article. For instance:

1) this argument makes the implicit assumption that the “number of years before a species goes extinct” is anti-correlated with “the present population of the species” meaning that the greater the present population in comparison to the historical population, the less time we should expect the species to survive for. This is already a contradiction because in reality it is the opposite. Species abundance is directly correlated with species longevity. Necessarily so! In order for a species to go extinct all members must die!

2) there’s no particular reason you should take the emergence of anatomically modern humans as the start point. We represent a continuous lineage of related animals going back to the last universal common ancestor of all life. By naive copernican principal, you may expect our lineage to go on for another 4 billion years! This is not to say that this is likely, just that the copernican principal is entirely subject to what you consider the starting point to be. If you say you care about “homo sapiens and their direct descendants” rather than “homo sapiens” you get a very different answer.

It's not most, but it's still remarkable that about 5% of humans who have ever lived haven't died.

To Whom It May Concern,

By reading this, you have confirmed your membership in the Five Percenters Club. Welcome.

Well, this text may be read by a person born in the future. It's hard to tell whether the population will keep growing or if it will fall by then. It's hard to make predictions, especially about the future

Even more remarkable is that by the estimate in Table 1, the percentage is increasing over time.

If this trend continues over the centuries it is conceivable that >=50% of all human beings to ever exist could be extantly alive. Either growth rate exploded or death rate arrested.

It recalls to mind Fyodor the one-time teacher of Tsiolkovsky of the rocket equation, who conceived a kind of akashic immortality project he called the Common Task. So like maybe this Kaneda-Haub statistic asymptotically approaches 100%.

Supposing a starting population of 2 we can call Adam and Eve divided by 0 dead ancestors do note it started at infinity before dropping precipitously near 0 for a 202k year exponential climb to today's ~7%. Fwiw I consider such plot affirmative evidence assuming the demographic inputs are not wildly inaccurate.

We're all outliers by still being around.

I've never heard most, but I think back the population of earth was only about 6 billion there were people claiming that about 1/5 of people who have ever lived are alive right now.

I've read that at the smallest bottleneck our species had fewer than 10,000 individuals, although I don't think that sad state lasted long.

There's a version of this that may actually be correct if you restrict it to the number of humans ever older than 60 years old, but I admit I never followed up on that one. The roughly 100 billion ever claim I recall more readily as it's an interesting remark to give to people who think they see ghosts to see what they think of it and the related question of where they all are.

Looks like that is false as well:

https://www.demographic-research.org/volumes/vol36/54/36-54....

According to that, it's between 5.5 and 9.5% for age 65, nowhere close to 50+%.

Why are the ghosts usually wearing clothes from the last few hundred years? Where are the Bronze Age ghosts? Or do ghosts dissipate after a period of time? Has anyone ever asked these questions of ghost believers?

It’s a catchy structure/fact that people use for many true things that reenforce misremembering false things. For example there have been many articles recently that more scientists are alive now than in all of history, which is probably true.

exponential growth is something our brains cant naturally process.

I think it's precisely this. We see exponential population growth of population, so we naturally assume most humans are alive now. What this intuition fails to grasp is quite how long humans have been around: eventually that adds up.

With a precise exponential the tail wouldn't really add up all that much. The integral to infinity is a finite number.

True. Maybe the fallacy is seeing exponential(ish) growth now, and pretending it was always exponential. Maybe population was linear(ish), for a very, very, long time.

It can't be exponential. If in 1800 there was 1G people, in 1900 2G people and in 2000 6G people, and we fit an exponential curve thought that we get less than 10 people alive in the year 0.

2007 Fact or Fiction?: Living People Outnumber the Dead

https://www.scientificamerican.com/article/fact-or-fiction-l...

Arthur C Clarke https://www.goodreads.com/quotes/212808-behind-every-man-now... "Behind every man now alive stand thirty ghosts, for that is the ratio by which the dead outnumber the living. Since the dawn of time, roughly a hundred billion human beings have walked the planet Earth."

also Snopes (updated 2007) https://www.snopes.com/fact-check/recount-your-dead/

no they don't. Here is the beginning of the Scientific Amercian article:

The human population has swelled so much that people alive today outnumber all those who have ever lived, says a factoid whose roots stretch back to the 1970s. Some versions of this widely circulating rumor claim that 75 percent of all people ever born are currently alive. Yet, despite a quadrupling of the population in the past century, the number of people alive today is still dwarfed by the number of people who have ever lived.

In 2002 Carl Haub, a demographer at the Population Reference Bureau, a nongovernmental organization in Washington, D.C., updated his earlier estimate of the number of people that have ever existed. To calculate this, he studied the available population data to determine the human population growth rates during different historical periods, and used them to determine the number of people who have ever been born.

For most of history, the population grew slowly, if at all. According to the United Nations' Determinants and Consequences of Population Trends, the first Homo sapiens appeared around 50,000 years ago, though this figure is debatable. Little is known about this distant past and how many of us there might have been, but by the time of the agricultural revolution in the Middle East in 9000 B.C., Earth held an estimated five million people.

Between the rise of farming and the height of Roman rule,population growth was sluggish; at less than a tenth of a percent per year, it crawled to about 300 million by A.D. 1. Then the total fell as plagues wiped out large swathes of people. (The "black death" in the 14th century wiped out at least 75 million.) As a result, by 1650 the world population had only increased to about 500 million. By 1800, though, thanks to improved agriculture and sanitation, it doubled to more than one billion. And, in 2002 when Haub last made these calculations, the planet's population had exploded, reaching 6.2 billion.

To calculate how many people have ever lived, Haub followed a minimalist approach, beginning with two people in 50000 B.C.—his Adam and Eve. Then, using his historical growth rates and population benchmarks, he estimated that slightly over 106 billion people had ever been born. Of those, people alive today comprise only 6 percent, nowhere near 75 percent. "[It is] almost surely true people alive today are some small fraction of [all] people," says Joel Cohen, a professor of populations at the Rockefeller and Columbia Universities in New York City.

... more at above link https://www.scientificamerican.com/article/fact-or-fiction-l...

i have the same (mis)memory.. where is this from?

Same here. I’m thinking the book Species maybe?

I wonder if there were old estimates based on religious teaching that Earth is only 6000 years old. We have only recently known the age of humanity and prehistoric population.

Or maybe it was saying that wasn’t based on estimate.

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