Every Peak in Earth's History Has Been Followed by a Drop Off

The history of life on Earth is not a smooth upward curve from simplicity to complexity. Randall describes it as a sawtooth - periods of rapid proliferation, dense with species and biological complexity, interrupted by event nodes at which the number of species drops dramatically and the fossil record shifts from prolific to sparse almost overnight. The Cambrian explosion is the most celebrated example of rapid speciation - but Randall notes it was followed by not one but five great mass extinction episodes, each defined by the sudden disappearance of a majority of all species on Earth. After each collapse, a threshold is eventually crossed, and the process of proliferation begins again.

What Randall finds most significant is how directly that biological model maps onto the rise and fall of human civilizations. The same sawtooth pattern - rapid development, catastrophic interruption, hiatus, and then renewed expansion - appears to govern human history with the same periodicity it governs the fossil record. By the late 1970s and into the 1980s, he notes, this framework was becoming increasingly difficult for science to ignore in biology. Randall’s argument is that it has taken considerably longer for the same logic to be applied to human prehistory - and that the resistance to doing so has left us with a fundamentally incomplete picture of how many times human civilization has built itself up, hit an event node, and been forced to start again.