The Descent ranks as one of the most subversive texts in human history. Darwin brands the view that man’s origin can never be known—that is, that it might lie beyond the reach of the human intellect to explain—as the product of ignorance, and he sets about showing that it is a problem that can be solved by science.

To say that man’s origin is explicable in scientific terms is truly a radical claim. Whatever it is that makes human beings distinct—our apposable thumbs, upright posture, and complex speech mechanism, as well as our literature, philosophy, and sacred texts—can be explained by the very same forces that shaped blue-green algae.

Human beings, in other words, are solely and entirely the products of natural forces. With a few strokes of a pen, Darwin lays the groundwork for the disenchantment of human nature and human affairs. For example, he opens chapter two of the first volume by declaring his intention to show that “there is no fundamental difference between man and the higher mammals in mental faculties.”

In sharp contrast to the Cartesian account of non-human animals as automata, Darwin declares it indubitable that non-human animals “feel pleasure and pain, happiness and misery.” Animals dream, dogs love their masters, and even insects play together. He even goes so far as to assert that “All animals feel wonder, and many exhibit curiosity.”

The subversive impact of these assertions lies not in the notion that many supposedly exclusively human traits are far from unique, but rather that these traits are not so remarkable as we suppose because they are the product of forces that natural science can describe and explain. To repeat, we are what we are, Darwin asserts, entirely by virtue of natural forces.

One of the longest-running debates in western thought concerns the relationship between the lower and higher. The Book of Genesis, Plato, and Augustine all posit that the lower can only be explained in terms of the higher. Darwin, by contrast, locates himself in the camp of thinkers such as Marx and Freud in arguing that the higher can and must be accounted for in terms of the lower.

In the Bible, for example, creation is often understood as a story of divine love. The world rests not so much on a foundation of matter in motion or laws governing the behavior of molecules, atoms, and subatomic particles, but on stories of how love brings the world into being and helps it to reach its full fruition. Action and reaction are less fundamental than adoration.

In Darwin, by contrast, the key ingredients for the world as we know it are scarcity, competition, and the struggle to survive and reproduce. The weak and infirm are continually culled out, as the forces of nature select for the best adapted among organisms. In Tennyson’s formulation, we are the perfectly natural byproducts of a pitiless nature “red in tooth and claw.”

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