BIOLOGY 1B Lecture Notes - Lecture 10: Permafrost, Demographic Transition, Overfishing
Document Summary
The spike in human numbers in recent centuries is stunning. In terms of volume, eight billion humans represent a relatively small quantity. Clearly, the strength and reach of humans is not based on size alone. Our behavioral, cognitive, and sociocultural connections and the tools we wield lend us a power, collectively, that defies our scrawny frames. On a global scale, human population size has grown exponentially. Tech, medical advancements, infrastructure, agriculture all affect the table below. Age structure pyramids are useful to summarize population structure and to assess future population trends. Divided into age groups with separate histograms for females and males. Societies that are in a growth phase are bottom heavy, with the majority of the population concentrated in the pre-reproductive age classes. In these societies, birth rates are expected to climb as individuals reach reproductive age. Societies that exhibit relatively slow growth exhibit the sort of balanced distribution evident for the united states (middle, below).
