A View from the Back of the Envelope top

How many people
Scale of some things
People seconds
Landmarks
[ Scale | Landmarks | Other ]

Some suggestions

How many people
ever 1011 1011, , ×0.2-2
Earth 6 billion 6 × 109, +4%, ±1%?
US 250 million 2.5 × 108, -6%, ±1%?
city 107 big, 106 mid, 105 small

Analysis

Human population of earth/world, US, cities, ...

Earth current pop
1010 x 0.577 ±<1% ??? CIA July 1996 estimate
[link broken - new site]
1010 +73%
6 x 109, six billion +4%

US current pop
108 x 2.66 ±<1% ??? CIA July 1996 estimate
[link broken - new site]
108 -62%
3 x 108, three hundred million +13%
2-3 x 108, two to three hundred million -25% to +13%, a 38% spread
2.5 x 108, two hundred fifty million -6%
2.7 x 108 +2%

City pop
1 to 30 million
107 big, 106 mid, 105 small
a million ± x 10
106 x {27 Tokyo, 15 NY, 5 Philadelphia, 3 Atlanta/Minneapolis, 1 Birmingham/Buffalo/Dayton/Omaha}
(8 Chicago, 6 Boston, 5 Washington, 4 Detroit/Toronto/Houston/Atlanta, 3 SanBernardino/Dallas/SanDiego)
(AltaVista "title:(cities AND population)")
The choice of 1 × 106 as a lower bound on "city-ness" requires examination.

Earth cumulative pop
1011×0.2-2

We have a rough historical population curve. How many individuals are there per unit time for a given population? Well (after some pondering, and getting it wrong several times), each slot in the population count is occupied by an individual for a `life expectancy' time, after which another individual takes it over. So life expectancy is the key. Bounds of say 80 and 20. Running 25 and 50 seems plausible. Though if infants which don't reach maturity are counted, something much lower might be needed.

Say 1 life / 25 or 50 years, or 2-4 lives / 100 yr.
1900 to present, 2-4 lives, 2 growing to 6 billion pop, say 10 billion. (4-24)
1800 to 1900, 2-4 lives, 1 to 2 billion, say 4 billion. (2-8)
1000 to 1800, 16-32, 3 to 8 108, say 15 billion. (5-26)
1 to 1000, 20-40 lives, 3 × 108, say 10 billion. (6-12)
10kYA to 2kYA, 160-320 lives, 107 to 8, say 10 billion. (2-32)
50kYA to 10kYA, 800-1600, 104? 6?, say <~1 billion. (0-1)
600kYA to 50kYA, 1-2 × 104 gens, 104? 5?, say <~1 billion. (0-1)
Adding it up... say 50 billion (19-104). Say 0.5 × 1011 ±×2.
I'm going to call it 1011. The low bound unfortunately falls out of 1011 into 1010..
Reducing the `how old before counted' threshold would nudge it back upward.
I am looking around for a closer estimate.

I note that roughly (<x2) about as many people lived >2kYA, AD 1-1000, 1000-1800, 1800-present.

Hmm... I wonder how much of our increasing rate of technological progress is simply the result of more warm bodies...?

My very first cut was this... If 1 generation per 20 yr,
homo sap: 106 x 10say 5 / 20 ~= 10~11
modern: 105 x 10say 6 / 20 ~= 10~11

Better homo sap: 105 to 6 (yrs) x 104 to 8 (ave pop) / 10 ~= 108 to 13.
Currently 1010, so say 1010 to 13.
Better modern: 0.4x105 (yrs) x 106 to 8 / 20 ~= 1010 to 12.
A bit too sloppy. Could use less off-the-cuff treatment.

Further notes (1998.May.11):

"The dead outnumber the living, in a ratio that could be as high as 20 to 1," a demographer, Nathan Keyfitz, wrote in a 1991 letter to the historian Justin Kaplan. "Credible estimates of the number of people who have ever lived on the earth run from 70 billion to over 100 billion."
The Wreck of Time - Taking our century's measure by Annie Dillard
Harper's Magazine, January 1998, p 51
The same article suggests "about half of all the dead are babies and children".

How Many People Have Ever Lived On Earth?, and a related note[broken].
How many people have ever lived?
Estimating The Number of People That Have Ever Lived
Historical Estimates of World Population
Historical World Population Estimates

A View from the Back of the Envelope
Comments encouraged. - Mitchell N Charity <mcharity@lcs.mit.edu> 

Notes:

Doables:
 link to relevant current factbook pages, rather than to site.
 area density - crowd estimation - 4/m^2 shoulder to shoulder "100%",
   6/m^2 pressing "150%", sitting "25%", walking freely "10%".
   Sketch area, assign densities, calc crowd.

History:
  2003-Dec-05  Repaired links - 1 flagged, 1 fixed, 4 added.
  2003-Feb-04  Repaired links - 2 flagged, 1 fixed, 1 removed, 2 added.
  2001-Feb-11  Fixed same link.
  1999.Feb.15  Added link to PRB's `How Many People Have Ever Lived On Earth?'.
  1998.Mar.11  Added Keyfitz's cumulative human pop estimate.
  long ago     Created.