Harris sets out to prove that ecology and reproductive factors had a big impact on the rise of populations like the Olmec, Maya, and Aztec in Mesoamerica. He outlines shifts in agriculture production and how that changed development in the Teotihuacan Valley and the Valley of Mexico. Hillside slash-and-burn farming was initially largely used, then the populations relied heavily on spring-fed canal irrigation, and finally the groups were dependent on chinampa construction. Chinampas can be described as floating gardens, though he points out they did not float, and seemed to be plots of crop in the middle of water. Check out the Rabbit Holes tab for a visual. The population trended larger and denser throughout these three modes.