Why Think? Evolution and the Rational Mind

Why Think? Evolution and the Rational Mind

Why Think? Evolution and the Rational Mind

Why Think? Evolution and the Rational Mind


In a world where natural selection has shaped adaptations of astonishing ingenuity, what is the scope and unique power of rational thinking?

In this short but wide-ranging book, philosopher Ronald de Sousa looks at the twin set of issues surrounding the power of natural selection to mimic rational design, and rational thinking as itself a product of natural selection.

While we commonly deem ourselves superior to other species, the logic of natural selection should not lead us to expect that nature does everything for the best. Similarly, rational action does not always promote the best possible outcomes. So what is the difference? Is the pursuit of rationality actually an effective strategy?

Part of the answer lies in language, including mathematics and science. Language is the most striking device by which we have made ourselves smarter than our nearest primate cousins. Sometimes the purely instinctual responses we share with other animals put explicit reasoning to shame: the movements of a trained athlete are faster and more accurate than anything she could explicitly calculate. Language, however, with its power to abstract from concrete experience and to range over all aspects of nature, enables breathtakingly precise calculations, which have taken us to the moon and beyond. Most importantly, however, language enables us to formulate an endless multiplicity of values, in potential conflict with one another as well as with instinctual imperatives.

In short, this sophisticated and entertaining book shows how our rationality and our irrationality are inextricably intertwined. Ranging over a wide array of evidence, it explores the true ramifications of being human in the natural world.


It’s fashionable to claim that we should trust our gut, rely on our intuitions, and stop thinking too much. The book now in your hands takes the question seriously: How is explicit human thinking different from the goal-directed “intelligence” of animals? How does our own ability to come to quick, intuitive decisions—often mediated by unreflective emotional responses—relate to reflective thought? The quick responses of intuition often conflict with reflective thought. Yet both have been honed and refined by millions of years of natural selection. So it’s important to understand how they both work, and what are their respective strengths.

Evolution itself has displayed a capacity to mimic intelligent planning so uncanny that many people simply refuse to believe it ever happened. That makes it worth asking what natural selection and intelligent thought have in common. Why did the inventive genius of the Wright brothers not enable them to design a 747 straight off the bat? If we ignore the time scale, the path from the Kitty Hawk “Flyer” to the supersonic airliner looks much like the transition from the early Eohippus to the modern horse, Equus Caballus: gradual, fumbling, step-by-step change, groping forward by trial and error. How then are “rational” solutions different from those arrived at by the mindless processes of natural selection?

This book approaches this question by looking at our nature as rational beings in the light of biology. We don’t usually accuse other animals of being irrational, even when their instinctual responses . . .

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