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Estimate the number of people since ever?

Rami asked on Apr 14, 2019 - 2 answers

Estimate the number of people since ever?

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updated his answer on Apr 17, 2019
BCG Consultant | MBA Stern | 100% interview success rate (8/8 incl BCG, A.T. Kearney, Strategy&) |Personalized interview prep

This is definitely a top-down (as opposed to bottom-up) sizing.First, I'll assume homo sapiens.

There's a lot of ways to approach this, but I would personally segment it by world population over time. I know that population growth is exponential, and I roughly know the population in different periods - however I have to be careful to account for "existence" i.e. birth/generations.

A lifespan is around 70, but I'll round down to 50 (which averages out across all of time).

  • I know there's about 7 billion people today.
  • Going back 50 years (1960s) there were around 4 billion.
  • 50 years again (1910s) that was around 2 billion
  • Now I'll keep that # but double the count to 100 years (in 1800s, 2 billion people). I.e. population was around a billion, but lets count it twice to account for births.
  • In 1700s, down to 1 billion (again, population of around 500 million?)
  • And I'll keep this 500 million x 7 down to the 1st millenium (3.5 billion).
  • Now, I'll drop it to mellenium, and keep 500 million down to when "civilization" emerged, around 4,000 BC. So, 500 million X 5 = 2.5 billion.
  • Then, we're into an extremely long tail for hundreds of thousands of years but very low population, so I'll throw in another 500 million.

If I were to draw this on a chart, it'd be exponential, so I'd a least be comfortable with that.

I'll add 7+4+2+2+3.5+2.5+.5 = 31 Billion people.

However, I know that, for most of history, death rates were absolutely horrid and that something like 50% of all people died before the age of 7. So, I'll multiply 31 billion by 1.5 to get the answer: 46.5 billion people have existed in the world.

Am I close?


Serhat replied on Apr 25, 2019
BCG | Kellogg MBA | 50% discount | 350+ coachees | 5+ year consulting | 30+ projects in ~10 countries

Hi Rami,

We are happy to provide you feedback on your solutions.

Would you want to try your best solution first? Happy to improve it together.



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