Age Pyramid Simulation

	A	B	C	D	E
1	Instructions: Download spreadsheet, change basic parameters, change data for seed population, then see what happens at each iteration. Each iteration is the time that a girl takes to become a woman, and a woman to become a grandma, so if that time is say 20-25 years, then there are 4-5 iterations (generations) per century.
2		1) Change basic parameters.
3	Fertility	1	Number of girls born from each woman.
4	Infant survival	0.9	Proportion of girls who grow to become adults.
5	Adult survival	0.7	Proportion of women who grow to become granmas.
6	Elder survival	0	Cero by definition, as there's no other age group.
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8		Girls	Women	Grandmas
9	1	1,000	1,000	1,000	2) Change data for seed population.
10	2	1,000	900	700	and 3) Watch what happens when your seed population evolves with your basic parameters.
11	3	900	900	630
12	4	900	810	630
13	5	810	810	567
14	6	810	729	567
15	7	729	729	510
16	8	729	656	510
17	9	656	656	459
18	10	656	590	459
19	11	590	590	413
20	12	590	531	413
21	13	531	531	372
22	14	531	478	372
23	15	478	478	335
24	See? With parameters 1, 0.9, 0.7 and gen 1 = 1000,1000,1000 the outcome is a tendency to demographic collapse after 15 generations = say 3-4 centuries.
25	Deep inside, cells B10 to D23 have formulas which take the previous generation and let it evolve further. Of course both internal collapse (or explosion) and external factors (other "tribes", resources, viruses, etc) change both the size of the population and the parameters which affect change.
26	Formula in B10 is "=C9$B$3", in C10 is "=B9$B$4", in D10 is "=C9*$B$5". Rows 11-23 (generations 3-15) are copied from row 10 (generation 2).
27	Change parameters and send your insights to @lucasgonzalez http://www.twitter.com/lucasgonzalez Thank you!
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