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How many human beings are/were there?

I'm spinning a story where a guy is chosen to represent the whole of humanity. In this story the minds of people who die are preserved in a cool sword that chooses to communicate with a single person every millennium or so. This enables the guy to glean info from any person that lives or has ever lived.

At some point in the story the guy complains that "I'm in charge of the survival of X billion people." I'd like to have some valid number there.

In short: How many human beings are there? That's an easy one (got some articles in Google), but on top of that, how many humans have died in the history of humanity?

I'd love to have an estimate in the millions, but would be grateful for a billions' estimate.

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    $\begingroup$ Given that roughly 360000 humans are born every day (according to a quick google search), any correct number down to millions would be obsolete by the time you publish your story. $\endgroup$ – Guran Aug 11 '16 at 8:33
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    $\begingroup$ Define "human"... $\endgroup$ – nzaman Aug 11 '16 at 8:44
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    $\begingroup$ If you count humans who died as a fetus, baby or infant, your number will easily be 2-3 times as high. So you'll have to draw a line about when a human mind is developed enough for the sword. $\endgroup$ – user2727 Aug 11 '16 at 9:18
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    $\begingroup$ Reminder to close-voters... $\endgroup$ – Frostfyre Aug 11 '16 at 14:31
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    $\begingroup$ @Guran Would be fun to have the character use this line multiple times and slowly increase based on this number. $\endgroup$ – David Starkey Aug 11 '16 at 14:50
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107 Billion according to the Population Reference Bureau. Details Here

Must warn that this can only be guessed and is based on arbitrary definitions of human.

What we call hominids (i.e., humans) go back further than the supposed 50,000 BCE, but you can do a rough estimate of 600,000,000 max at any point (the maximum capacity of Earth to handle Hunter Gatherers it is assumed) before around 10,000 BCE, with an average life span of 60 years (adults...double the number for children). This means roughly 50 years between complete replacement so we can just calc 600m x 4 (accounting for the full replacement and children that died) for every hundred years.
2.4b/century at 2 to 50 million years would be 240,000,000,000,000/million years so 480 trillion to 12 quadrillion, half of which would be 15 or under and 80% of those 5 or under. More than 99% of all of them being very primitive pre-historic people.

106 billion is the upper limit of "Civilized humans"
50 billion is around the upper limit of "humans lived post-Greek world"
34 billion that lived during and after the crusades
10 billion that have lived in the last 100 years and you could relate to

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    $\begingroup$ Are your numbers just for Homo Sapians, or are we unable to determine how many Homo Sapians alone have ever existed? $\endgroup$ – SGR Aug 11 '16 at 8:13
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    $\begingroup$ 600m (If I recall correctly) is the estimate for how many hunter gatherers are sustainable on Earth. Home Sapiens haven't been on Earth alone for the majority of that time so only a fraction of that would be Homo Sapien. Also I may have got the 50m year wrong. Not sure. didn't fact check. But it's an arbitrary line so you have to explain that anyways. You could say they link to everyone from x generations back and then forward and you can give a number in line with the numbers in that link. $\endgroup$ – Durakken Aug 11 '16 at 8:57
  • $\begingroup$ Cheers. I see that this article was found by two people while my own googling skills got me nothing.. $\endgroup$ – Nahshon paz Aug 11 '16 at 14:42
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According to this article - How Many People Have Ever Lived On Earth? 108 Billion

Year        Population  Births per 1,000    Births Between Benchmarks
50,000 B.C. 2               -               -
8000 B.C.   5,000,000       80              1,137,789,769
1 A.D.      300,000,000     80              46,025,332,354
1200        450,000,000     60              26,591,343,000
1650        500,000,000     60              12,782,002,453
1750        795,000,000     50              3,171,931,513
1850        1,265,000,000   40              4,046,240,009
1900        1,656,000,000   40              2,900,237,856
1950        2,516,000,000   31-38           3,390,198,215
1995        5,760,000,000   31              5,427,305,000
2011        6,987,000,000   23              2,130,327,622


NUMBER WHO HAVE EVER BEEN BORN                    107,602,707,791
World population in mid-2011                        6,987,000,000
Percent of those ever born who are living in 2011   6.5
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    $\begingroup$ Why did you post an answer providing the exact same information from the exact same source as Durakken, but three hours later? $\endgroup$ – Frostfyre Aug 11 '16 at 12:26
  • $\begingroup$ It wasn't until you posted this comment that I realized that our sources were the same. :( $\endgroup$ – Jimmery Aug 11 '16 at 12:49
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    $\begingroup$ A population of 2... Sounds a little biblical. $\endgroup$ – UIDAlexD Aug 11 '16 at 13:31
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    $\begingroup$ @Ryan Evolution states that reproductive isolated populations will incur genetic drift until viable offspring become increasingly less likely if not impossible between the isolated populations. There's no point where you can draw a line and say "This is species X, which has just now given birth to species Y with this individual." There's never just one member of a species, because if there was that species would be extinct in a generation. $\endgroup$ – UIDAlexD Aug 11 '16 at 16:34
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    $\begingroup$ @Ryan True, but that line is always moving, and it's a blurry one because - as you said - there won't be a sharp drop in fertility. Saying that a species dates back to a certain era is at best an accounting trick to cope with infinite regress, not a reflection of reality. $\endgroup$ – UIDAlexD Aug 11 '16 at 16:58

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