scala naturae

The above examples illustrate several misunderstandings of nervous-system evolution. The first problem is that these ideas reflect a scala naturae view of evolution in which animals can be arranged linearly from “simple” to the most “complex” organisms. This view is unrealistic in that neural and anatomical complexity evolved repeatedly within many independent lineages. This view also implies that evolutionary history is a linear progression in which one organism became another and then another. It is not the case that animals such as rodents, with “less complex” brains, evolved into another species with slightly more complex brains (i.e., with structures added onto the rodent brain), and so on, until the appearance of humans, who have the most complex brains yet.

2020, Joseph Cesario, David J. Johnson, Heather L. Eisthen, “Your Brain Is Not an Onion With a Tiny Reptile Inside”, in Current Directions in Psychological Science, volume 29, number 3