Evolution of thought and emotion

Abstract

What started as a self-scrutinizing exercise turned into an extraordinary volume on a journey in search of the origin of survival mechanisms and consciousness. Joseph LeDoux — the undisputed guru of emotions and the Henry and Lucy Moses Professor of Science at New York University — declares in The Deep History of Ourselves that the notion of an ‘amygdala fear center’ that became not only a scientifi c doctrine but also a cultural meme is dead wrong. Since his writings contributed to this mischaracterization, LeDoux feels that he has some explaining to do. He does this in the form of beautifully composed prose of 400 pages. Without hesitation, he tells the reader up front that, in order to accomplish his goals, a “radical approach is needed”. This is done in the form of two interconnected journeys, the fi rst of which is the evolution of survival circuits: “there is indeed good evidence that the same brain systems control survival behaviors in humans and other mammals”. However, these are not the systems that are responsible for the conscious feelings that we experience when we engage in such behaviors and, therefore, he postulates the need of another system that is uniquely human. To contrast these two lines of ideas, the author reaches back through four billion years of natural history. The elaborate discussion on our long past is done not for the sake of cataloguing facts but to seek answers to a complex problem: the origin of our phenomenal or access consciousness. In the process, two new LeDouxs unfold: LeDoux the evolutionary biologist, evo–devo guy and a consciousness expert. Book review To understand the brain, fi rst one needs to know about the body it controls. And bodies are complex too, even if they started out simple. Living things must borrow energy from the physical world to survive and prosper. This fundamental survival strategy began way before cells with organelles and protective boundaries developed, initially using the simplest forms of chemotaxis and tropism before adopting more elaborate approach–avoidance strategies. LeDoux — the naturalist — shows impressive expertise in the development of everything that matters to life. We learn how bacteria adapted to changing temperature and oxygen levels by acquiring “internal molecular representations of environmental conditions”. He teaches us that memory is already present in unicellular protists — no need for a complicated brain — in the service of maintaining energy supplies, balancing fl uids and osmolarity, and defending against harm. These are the deep roots of the “survival states”. He delves into the debate about the priority of DNA versus RNA, explains how compartmentalization of complex molecules eventually gave rise to subcellular units, and guides us through the emergence of archaea, bacteria, the merging of existing life forms, and the advantages of sexual multiplication. I particularly enjoyed the discussion on the continuity of the general Bauplan (body plan) that sets the architectural features common to many members of the same phylum, and along the way I learned to respect simple organisms even more than before. LeDoux is a patient and skillful teacher who is well familiar with the reader’s attention span and the need to pause for thought, contemplate, and get ready for the next chunk of novel information. Chapters consisting of typically two to four pages and half a page of blank paper are good reminders to take a deep breath and internalize the presented material. His story is greatly enhanced by uniform illustrations from the same artist, an effective aid to ease the reading. By the end of the fi rst part, the author had convinced me that “a key part of our story is [...] how nervous systems came to be”. Yet, as I had just