Basic demography

The four basic demographic FACTS (events that happen to people) are: Birth, Death, Marriage and Migration; these can expressed as four population VARIABLES, and measured as rates: Fertility, Mortality, Nuptiality, and Mobility

A population is often arbitrarily delimited (Rockbridge county, Tokyo) but can be treated as a unit that persists over time, and provides a spatial container for these processes. We can model what happens in a population as a tank with inflow and outflow pipes, and valves whose settings affect the level in the tank. The fundamental question: what forces influence the settings of the valves? (What increases or decreases inmigration and outmigration? What raises and lowers birth and death rates?)

That's clear enough for B, D and Mig, but somewhat murkier for Marriage.

We want to know the answers to empirical questions about the structure of populations at any given time, and processes in populations. Their explanation generally involves cultural factors --and there's a sense in which Demography is the Geography of Human Cultures.

But let's begin with some observations about the big picture of the globe's population, and then later we'll go back to the individual and local population scale levels:
How Many People Have Ever Lived on Earth? by Carl Haub

How Many People Can the Earth Support by Joel Cohen --and see a quick summary of the argument, and Population Growth and Earth's Human Carrying Capacity Joel E. Cohen Science, New Series, Vol. 269, No. 5222. (Jul. 21, 1995), and Population Reference Bureau Data Finder and 2003 World Population Data Sheet ...see also United Nations Population Information Network and U.S. Census Bureau's International Data Base

And where are they? How are people distributed across the globe?

FACT or anyhow FACTOID: more than 50% of humanity lives in cities. ??What does that do to 'culture'?? (e.g., for most urban dwellers, mass media are ESSENTIAL parts of daily life, and so they are tied into the worlds of electrons, into [potentially] global information systems. A very long way from the autochthonous cultures still sustainable in 1900 [when 12-15% were urban] or even 1950 [30% urban]. Social control operates very differently in face-to-face "traditional" societies than it can in the more anonymous urban settings. "Moral codes" just aren't as effective in cities, and so on...)

"In cities, at least where child labor is uncommon, children are costly to their parents for 15 or 20 years, whereas in rutral settings, especially where there are goats and chickens to tend, children from the age of 5 or so are economically useful." (McNeill and McNeill 2003:283) --part of the explanation of fertility decline in cities.

WHY the (historically utterly unprecedented) population growth of the last 50/100/200 years?

  1. death control

  2. fossil fuel subsidies, affecting transport and production
"In the process of trying to feed ourselves, make money, and protect ourselves from our fellows, we recast the biosphere dramatically, inserting ourselves as the main force shaping biological evolution." (McNeill and McNeill 2003:293)

"At present, human society is one huge web of cooperation and competition, sustained by massive flows of information and energy." (McNeill and McNeill 2003:322)

That's a lot to work with, each element being something we could spend the next 10 weeks on and barely scratch the surface.
Population pyramids

UN Cyberschoolbus

Population Growth Case Study: China has a nice animation ...and one for the US

US sex ratios animated

expected age at death animated