You would first note that in the graph, time is shown on the x axis and population size on the y axis. You would find the year 1800 (three-fifths of the way between 1500 and 2000 on the x axis) and trace straight upward to determine the approximate value of the data in that year. You’d then do the same for today’s date at the far right end of the graph.
To calculate roughly how many people are alive today for every one person alive in 1800, you would simply divide today’s number by the number for 1800. Two phenomena triggered our remarkable increase in population size. The first was our transition from a huntergatherer lifestyle to an agricultural way of life. This change began about 10,000 years ago and is known as the agricultural revolution. As people began to grow crops, domesticate animals, and live sedentary lives on farms and in villages, they produced more food to meet their nutritional needs and began having more children.
The second phenomenon, known as the industrial revolution, began in the mid-1700s. It entailed a shift from rural life, animal-powered agriculture, and handcrafted goods toward an urban society provisioned by the mass production of factory-made goods and powered by fossil fuels (nonrenewable energy sources including oil, coal, and natural gas.
Industrialization brought dramatic advances in technology, sanitation, and medicine. It also enhanced food production through the use of fossil-fuel-powered equipment
and synthetic pesticides and fertilizers.