15

I don't know if this question belongs precisely at History.SE, but I can't think of a more fitting alternative.

I've heard the estimate several times that about 100 billion humans have existed throughout human history. (I guess this depends somewhat arbitrarily on when you start counting our ancestors as human, but let's say we've settled on a fixed beginning moment and work with that for the rest of this question.)

When had half of all humans who have ever existed (until today) been born already? If the 100 billion number is correct, then I'm asking when the 50 billionth person was born.

Note that whatever the answer is, we can say that most of the humans who have ever existed were born after that date (or since slightly before that date).

  • 'somewhat'? I think we need a better definition. Ignoring the morality of the situation, perhaps it's the earliest proto-human with which a modern human could successfully mate? – Strawberry Dec 13 '19 at 13:52
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    The last paragraph seems contradictory. "most humans were born after that date" Wouldn't it be the case that half were born after that date and half before that date? In fact, 50 billion would have been born before that date and 50 billion after. – Loduwijk Dec 13 '19 at 16:56
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    @Loduwijk Hence the "or since slightly before that date." It only takes half + 1 person to become "most." – WillG Dec 13 '19 at 17:53
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    I know that the results returned by Google vary by geographic location etc., but the page cited in the answer below comes up as the 3rd result on the first page when I copy/paste your question into Google. Per our Help Centre, this site is not about "Questions answered by a simple Google search or to be found in a Wikipedia page". – sempaiscuba Dec 13 '19 at 22:49
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Data published by the demographer Carl Haub and Dr. Toshiko Kaneda in How Many People Have Ever Lived on Earth? on the Population Reference Bureau (PRB) website suggests that the 50 billionth person would have been born around 130 AD / CE. This can be seen by looking at the column 'Number Ever Born' in the table below:

enter image description here

Image source: Population Reference Bureau (PRB). Table data sources: Toshiko Kaneda and Genevieve Dupuis, '2017 World Population Data Sheet' (Washington, DC: Population Reference Bureau, 2017); United Nations Population Division, 'World Population Prospects: The 2017 Revision' (New York: United Nations, 2017).

In 130 AD:

  • Hadrian was emperor of Rome.
  • The Han dynasty ruled in China.
  • The Kushan Empire was around 100 years old and had about another 245 years to go.
  • Claudius Ptolemy, Greek mathematician, astronomer, geographer and astrologer, was probably in his 30s.
  • Galen, Greek physician, surgeon and philosopher, was an infant and would have been close to being the 50 billionth person born.

Carl Haub originally made these calculations in 1995 to dispel the myth that

The human population has swelled so much that people alive today outnumber all those who have ever lived

(His data estimates showed that "those alive in 2002 constituted only about 6 percent", far from the 'myth' of more than half.)

He and Toshiko Kaneda updated the data in 2002 and 2011, conceding that their approach is (of necessity) "semi-scientific". On the methods used in their calculations, the authors say that

calculating the number of people who have ever lived is part science and part art. No demographic data exist for 99 percent of the span of human existence. Still, with some assumptions about prehistoric populations, we can get a rough idea of this historic number...

They take 50,000 BC as the starting date:

Fixing a time when the human race actually came into existence is not straightforward. Hominids walked the Earth as early as several million years ago, and various ancestors of Homo sapiens appeared at least as early as 700,000 B.C. According to the United Nations Determinants and Consequences of Population Trends, modern Homo sapiens may have appeared about 50,000 B.C.

This corresponds "to the start of the Upper Paleolithic" and "the emergence of full behavioral modernity" ("behavioral and cognitive traits that distinguishes current Homo sapiens from other anatomically modern humans, hominins, and primates.").

The articles How Many People Have Ever Lived on Earth? and Do Living People Outnumber the Dead? go into details on how the estimates were arrived at (the details are a bit lengthy to include here...).

The margin of error for the birth of the 50 billionth person who ever lived is fairly large; Hadrian may not have been born or Galen may have been dead and buried rather than an infant, but the Kushan empire and the Han dynasty cover considerably longer time periods.

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    Great find! I thought we were going to be reduced to doing our own calculus. :-P – T.E.D. Dec 13 '19 at 6:44
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    Interesting - when did they start counting? (Since evolution is so gradual) – colmde Dec 13 '19 at 10:22
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    @ebv See updated answer. Yes, 'cute' is one way of putting it :). The authors readily concede that assumptions have been made, and they have not started with anatomically modern humans but rather behavioral modernity. – Lars Bosteen Dec 13 '19 at 13:00
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    @baudsp: Depends on your assumptions - and thus when you start counting. As T.E.D.'s deleted answer shows, the sheer length of the left-side tail is hard to comprehend, and has much more area than seems intuitively possible. – Pieter Geerkens Dec 13 '19 at 14:55
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    @LarsBosteen if this is the chosen definition, the choice of "2" as the earliest population seems incorrect and misleading. If you can isolate a population of exactly two who are "behaviorally modern" then before the younger of them was born the population was 1. And the choice of "2" somewhat implies that all other behaviorally modern humans are descended from one behaviorally modern human couple, which I'm sure is quite far from prevailing ideas in natural history research. – Will Dec 13 '19 at 17:21

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