In part one I let Charles Darwin speak for himself about the eye and the sterile insects, two difficulties he placed at the center of his own book. I continue in the same spirit, with his words identified so you can check them, and come now to the objection he considered gravest of all.
The fossil record
Darwin’s theory predicted an unbroken chain of intermediate forms linking one species to the next. The fossil record, as he knew it, did not show that chain. He put the problem to himself directly in Chapter IX:
Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory.
The most obvious and gravest objection. That is his own assessment, not a critic’s. His answer was that the record itself is radically incomplete: fossilization is rare, whole formations are missing, and the history of life survives only in scattered fragments.
The explanation lies, as I believe, in the extreme imperfection of the geological record.
Here the later history is genuinely mixed, and an honest account should say so. Two years after the Origin appeared, Archaeopteryx, a fossil with features of both reptiles and birds, was described, and many took it as exactly the intermediate Darwin had predicted. Many transitional forms have been cataloged since. Yet the pattern of abrupt appearance and long stability that troubled Darwin remained a live discussion well into the twentieth century, prompting proposals such as punctuated equilibrium in the 1970s. The difficulty did not evaporate; it generated more than a century of argument over how the record should be read, and a thoughtful reader may weigh for himself how completely it has been answered.
The peacock’s tail
Other difficulties Darwin confessed only in private. Animal ornamentation, beautiful yet seemingly useless for survival, bothered him to the point of physical discomfort. In April 1860 he wrote again to Asa Gray:
The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick!
The line is half a joke, but the trouble behind it was real. A theory built on utility had to account for extravagant display that served no obvious use. Darwin eventually answered with a separate mechanism, sexual selection, developed at length in The Descent of Man in 1871. Here, too, he did not pretend the problem away. He felt it, admitted it, and worked at it for years.
The objections that forced revisions
Not every difficulty came from inside Darwin’s own head. Two of the sharpest were pressed on him by others, and both changed how he wrote later editions of the Origin.
The first came in 1867 from the engineer Fleeming Jenkin. Under the blending theory of inheritance accepted in Darwin’s day, Jenkin argued, any single favorable variation would be diluted out of existence within a few generations, like a drop of ink stirred into water. Darwin had no satisfying reply, and given what was then known about heredity, the difficulty was real. It was resolved only after his death, when the rediscovery of Gregor Mendel’s work showed that inheritance is particulate rather than blending, so a favorable variant passes on intact.
The second came from the physicist Lord Kelvin. From the rate at which the earth was cooling, Kelvin calculated that the planet was far too young to allow the vast stretches of time Darwin’s gradual process required. Darwin counted this among the gravest objections to his views. It, too, was answered only later, when the discovery of radioactivity revealed a heat source Kelvin had not known about and pushed estimates of the earth’s age dramatically upward.
These two episodes matter because they show Darwin working without answers he genuinely did not have. On inheritance and on the age of the earth he was, by the standards of his century, stuck. The resolutions arrived from fields that did not yet exist when he wrote.
What the admissions do and do not show
Put these passages side by side and they tell one consistent story, and it is not the story told on either side of the argument.
They do not reveal a Darwin who secretly doubted that evolution had happened. On descent with modification he never wavered, and no credible record of a recantation exists. The familiar deathbed conversion story attributed to a “Lady Hope” was disowned by Darwin’s own daughter and is regarded as fiction by historians of every persuasion. It has no place in a serious discussion.
What they do show is a man of rare intellectual honesty. He understood that a theory is tested by its hardest cases, so he hauled his own hardest cases into the open. Some, by his own description, staggered him; one looked fatal. The eye gave him a cold shudder; a peacock’s feather made him sick. And then, case by case, he argued that each difficulty could be met.
That honesty is exactly what makes the Origin worth reading closely instead of quoting selectively. Some of the difficulties Darwin named were later addressed by discoveries he never lived to see, in genetics, in physics, in paleontology. Others are still argued over today. You are free to judge which of his answers satisfy you. I have made my own judgment, and readers of this site know where I stand. But any judgment should rest on the full record, in Darwin’s own words, never on half a sentence with the rescue clause removed.
Darwin gave us his difficulties plainly. The least we owe him, and ourselves, is to read them the same way.
A note on sources and editions
Quotations follow the first edition of On the Origin of Species (1859), chapters VI, VII, and IX. The letters to Asa Gray of February and April 1860 are in volume 8 of The Correspondence of Charles Darwin, searchable through the Darwin Correspondence Project. Sexual selection is developed in The Descent of Man (1871). Fleeming Jenkin’s objection appeared in his 1867 review of the Origin in The North British Review. Chapter numbering shifts in the sixth edition of 1872, where a chapter of miscellaneous objections was inserted: the fossil record chapter becomes Chapter X, and “gravest objection which can be urged against my theory” was softened to “serious objection which can be urged against the theory.”
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