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  ******  Population Growth displayed as Pyramids ******



 The pyramid is the traditional way to look at populations.

 Population is displayed as the number of males and
 females in 20,  5-year 'cohorts'.
 This is usually used statically, to show as a snap
 shot the present situation, or as an animation of
 past data & future predictions.

 A steeply declining pyramid indicates Third World.
 High numbers of births but high death rates.

 The developed world tends towards a shape with few
 deaths until late middle age.

 Population growth, and the growth and decline of
 nations, have fascinated mankind for millennia.
 Scientists like Malthus first seriously raised
 some of the issues, picked up later in the Sixties
 by the Club of Rome..


 Have you now seen the population, which started
 as a very unusual distribution, evolve into
 the classic 'developed world' shape?

 You may now care to reduce the delay loop so
 a complete run is faster, if you simply want
 to see the trend.

 Did you notice females dying off later than males?
     Unfair!!
 Did you notice teenage males die off rather quickly?
     What can you do about that?


 I am part of the 'baby boom' bulge immediately
 after WW II. You can see 'echoes' of that still
 in European & US pyramids.



 It is inevitable, since I've built in our
 typical current Population dynamics.
 They mean that whatever unlikely
 start population you try, you will end with
 exponential growth or decay.

 Total population will not be static without
 continual changes- natural or otherwise.
 It is almost impossible to get a balance,
 except by social feedback continually
 altering the death and birth rates.

 The added buttons give you a chance to try to
 stabilise population.
 I assume starvation hits all ages but parents
 starve themselves to feed middle-aged-children
 while babies starve.
 Wars hit almost all ages now- they used to kill 
  mainly men from 15 to 35.
 Baby boom is a sudden confidence or wealth which
 makes lots of families decide to have more children.
 End of boom is when a recession or similar reduces
 everyone's confidence in the future.


 Be extreme!
    Kill everyone off at 40!
    Insist on exactly two babies per couple!!
 All you have to do is try different
 birth and death rates-
 and NO-ONE need die or be killed!

 No rigid arrangement can be stable....
 Traditionally the natural controls were the 
 Four Horsemen of the Apocalypse.
    Famine
       War
          Pestilence
             Death ( of natural causes)

 'Civilisation' has increasingly affected all of these,
 but it has also created new cultural expectations.
 We are exposed far less now in our 'First World' to
 the high incidence of the first three Horsemen that
 even our parents experienced; and natural death rates
 are significanly better than even fifty years ago.

 I can thoroughly recommend some websites for further
 appraisal. Some have data for different countries, and
 many have lovely Java animations similar to my LB.
 But you cannot tinker with the rates in their closed
 simulations- which is why I knocked up this one.



 NB I have assumed that birth rates depend on the number
 of females ( and birth rates) only.
 In practice, if there is a shortage of men relative to
 women it will reduce birth rates a bit- and if there are
 no men then clearly there can be no births.
 I have also not included information about male
 fertility or relative ages of typical couples...

 Some day????


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			To-dos

  Add a cohort label down the centre.
  Flush in case another window is moved over.
  Make the display of labels and values of year and pop. look better.
  Add a library of rates.csv for real countries rather
      than use data statements.
  Add an option to scale vertically logarithmically so you get a
      straight line and see small-pop'n stage in more detail.
  Add web links to the good on-line resources.

 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  DONE		Position window more carefully.
  DONE		Add horizontal grid lines.
  DONE		Add a vertical line every 100 years
  DONE		Add ability to interrupt and alter rates,
                         and add random plagues or wars.
  DONE		Add screensave and print.
  DONE		Add a spinner to control update speed.
  DONE		Add buttons to change rates mid-calculation.
  DONE          Swap colours- pink for boy, blue for girl.
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