On the Origin of Species

Overview

Darwin had the theory by 1838 and published in 1859, after twenty years of barnacles, pigeons and letters, and only because Alfred Russel Wallace sent him an essay from Ternate that contained the same idea. The Origin was written at speed as what Darwin called an abstract of a much longer book he never finished.

It is not a difficult read. There is no mathematics, the prose is Victorian but plain, and Darwin explains everything twice. What makes it demanding is its length and its method: he is building a case from an enormous accumulation of small evidence, and he wants you to feel the weight of it.

The structure is unusual and deliberate. The first four chapters make the argument. The next four attack it, taking the strongest objections Darwin can find. The last five show how much the theory explains that nothing else does. He called it one long argument, and it is closer to a legal brief than to a textbook.

The argument

Chapter 1 starts at home, with domestic pigeons. Breeders produce pouters, fantails and tumblers from one wild rock pigeon by selecting which birds breed. Variation exists, it is heritable, and selecting it accumulates change. Chapter 2 shows the same variation in the wild, and notes that naturalists cannot agree where species end and varieties begin, which is what you would expect if species were varieties that had diverged far enough.

Chapter 3 supplies the force. Darwin takes it from Malthus: populations increase geometrically, food does not, so more individuals are born than can survive. He works the arithmetic for elephants, the slowest breeders he can find, and gets millions in a few centuries. Struggle follows necessarily, and it is often struggle with other members of the same species.

Chapter 4 puts the two together. If variation exists, if it is heritable, and if more are born than survive, then any variation that helps will tend to be preserved. That is natural selection, and it requires no foresight. Darwin adds divergence: the more different the descendants become, the more different niches they can occupy, so selection pushes them apart. The one diagram in the book, a branching tree, shows the result, and classification becomes genealogy.

Then he turns on himself. Chapter 6 handles difficulties: organs of extreme perfection, and he takes the eye directly, arguing from the gradations that exist in living animals from a light-sensitive patch upward. He states the condition that would destroy his theory, and it is a genuine one. Chapter 7 handles instinct, the cell-making of the hive bee and the slave-making ants. Chapter 8 handles hybrid sterility. Chapter 9 concedes that the fossil record is against him, and argues that the record is a book of which only scattered pages survive.

The last chapters are the positive case: succession in the fossil record, geographical distribution and oceanic islands, embryology, rudimentary organs, the strange facts of classification. Each is odd on the assumption of separate creation and expected on descent with modification. The book ends with the tangled bank and the sentence about endless forms most beautiful.

How to read it

Read the first edition, which is what Penguin and Oxford print. Darwin revised six times under attack, importing Lamarckian inheritance and hedging, and the sixth edition is a weaker book. The phrase “survival of the fittest” is Herbert Spencer’s and does not appear until the fifth.

Read chapters 1 to 4 carefully, then 6 and 9, then the last chapter. The middle chapters on hybridism and the detail of geographical distribution can be skimmed on a first pass. If your course assigns extracts, that will be roughly the selection.

Remember what Darwin does not have. He has no genetics: Mendel’s paper existed and went unread, and Darwin’s own theory of blending inheritance would have destroyed new variations before selection could act on them, an objection raised in his lifetime that he could not answer. He has no accurate age for the earth. The theory was completed by other people over the following eighty years.

Watch how he handles the eye, because it is the model for how the whole book works. He does not claim to know how the eye evolved. He shows that a graded series of working eyes exists now, so no step requires a leap.

Notice that human beings appear once, in a sentence near the end promising that light will be thrown on man’s origin. That was strategy. He published on that in 1871.

The common misreading is that this is a book about progress. Selection has no direction and produces no ladder. Darwin crossed out the word “higher” in his own copies.

Questions it raises

• Darwin argues from breeders to nature by analogy. Breeders have intentions and nature does not. How far does the analogy carry?
• He says his theory would break down if any complex organ could not have formed by successive slight modifications. Is that falsifiable in practice, or only in principle?
• If natural selection explains adaptation without purpose, what happens to the sense that living things are for something?
• The fossil record was Darwin’s worst problem and he answered it by appealing to what has not been found. When is that a legitimate move in science?
• Darwin keeps a Creator in his final sentence from the second edition on. Is that conviction, caution, or irrelevant to the argument?
• The subtitle speaks of favoured races in the struggle for life. What work is that language doing, and what did others do with it?