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© Nick Vokey
Emotions don't get in the way of rational thought, says Antonio Damasio . They make it possible.

The age-old distinction between the heart and the head is completely wrong. That's one of the central ideas in The Strange Order of Things, a new book by Antonio Damasio, a professor of neuroscience at the University of Southern California.

Emotions and feelings are often regarded as evolutionary relics handed down to us from an ancestral "reptilian brain" - mere physiological responses that cloud our ability to think rationally. According to Damasio, however, we underestimate the importance of feelings in our lives-and for civilization itself.

Damasio is a leading researcher on the nature of consciousness and first proposed a version of this idea, the "somatic marker" hypothesis, in 1994. He argued that the brain and the body work together to generate consciousness of the self within one's surroundings. Far from being vestigial responses, feelings influence higher-order thought processes such as decision-making. But in The Strange Order of Things, Damasio takes it much further, suggesting that feelings and emotions were the main driving forces behind human achievement.

Damasio makes this argument by expanding on the biological concept of homeostasis. Conventionally, homeostasis is taken to mean a set of regulatory mechanisms by which cells keep their functions and metabolite concentrations within a certain range, to maintain an internal environment conducive for life to flourish. But Damasio thinks that definition is too narrow. He argues that homeostasis is also at play beyond the cellular scale and includes the regulation of feelings and emotions.

Organisms strive for pleasant feelings and emotions that promote well-being, rather than unpleasant ones, which can be detrimental to health. In other words, homeostatic mechanisms not only maintain order within single cells but also play the critical role of "life regulation," tipping the balance toward positive feelings and emotions. And emotions, combined with creative intelligence, led to what we call culture: art, music, and poetry were developed because of their positive affect, and medicine emerged out of the need to alleviate pain and suffering.

Damasio extrapolates this yet further, to suggest that these homeostatic life-regulation mechanisms govern not just the behavior of individuals but also that of larger groups of people, as well as political and economic systems, which could be viewed as devices that were invented to help humanity flourish as a whole. This constant striving for positive emotions and well-being is a double-edged sword: it led to science and technology, which continue to improve the human condition, but also to failed governments, and weapons of mass destruction, causing much suffering.

If that doesn't seem ambitious enough, the picture Damasio paints is much bigger still. Taking the origins of life itself as his starting point, he charts the emergence of sensing and feeling. Bacteria are adept at sensing and responding to chemical cues and they, too, show "a determined desire to endure" and flourish, but only organisms with complex nervous systems that can form and manipulate mental images are capable of "feeling." The subjectivity that comes with such feelings is a key component of consciousness.

The idea that things happening in the body can impact brain function is now gaining wide acceptance. Damasio's somatic marker hypothesis - itself based partly on the ideas of the pioneering William James a century earlier - pre-empted the modern scientific study of interoception, our sense of what is happening in the body. New research is beginning to reveal just how physiological signals such as the heartbeat can influence brain function.

The claim that emotional regulation plays a role in economics is not as new. There is an old saying on Wall Street that the market is driven by greed and fear, and Adam Smith argued over 200 years ago that individuals acting out of self-interest make society as a whole better off, because of the "invisible hand" of market forces. Nonetheless, Damasio's main thesis - that homeostatic "life regulation" mechanisms led to cultural innovations and organizational behavior - challenges economic models that rely on Smith's "invisible hand" mechanism, and will surely fuel some debate.

Using homeostasis to explain everything from armed conflict to financial crises seems over-ambitious. Nonetheless, this is a thought-provoking book that provides a novel perspective on consciousness and social behavior. Unlike many others, it acknowledges the role of the body and, refreshingly, attributes feelings and consciousness to a wide variety of other animals.

At the end of a journey that takes us from single cells to brains and minds capable of conscious awareness, Damasio acknowledges how little we still know. But the final destination is not as important as his interesting speculative detours. For example, there are similarities between the primitive nerve nets found in brainless animals like jellyfish and the clusters of neurons in the enteric nervous system in our digestive tract. This part of our gut - which is crucial for interoception - could be thought of as the first brain, just as meaningful as the one in our heads.