—WILLIAM SCHWENCK GILBERT,
THE GONDOLIERS

The title of this chapter is taken partly from William Shakespeare’s The Tempest, but as we shall soon see, it poetically captures the essence of Darwin’s blunder. The source of the blunder was the fact that the prevailing theory of heredity in the nineteenth century was fundamentally flawed. Darwin himself was aware of the existing shortcomings, as he confessed candidly in The Origin:

The laws governing inheritance are quite unknown; no one can say why the same peculiarity in different individuals of the same species, and in individuals of different species, is sometimes inherited and sometimes not so; why the child often reverts in certain characters to its grandfather or grandmother or other much more remote ancestor; why a peculiarity is often transmitted from one sex to both sexes, or to one sex alone, more commonly but not exclusively to the like sex.

To say that the laws of inheritance were “quite unknown” was probably the most glaring understatement of the entire book. Darwin had been educated according to the then widely held belief that the characteristics of the two parents become physically blended in their offspring—as in the mixing of paints. In this “paint-pot theory,” the heredity contribution of each ancestor was predicted to be halved in each generation, and the offspring of any sexual partners were expected to be intermediates. In Darwin’s own words: “After twelve generations, the proportion of blood, to use a common expression, of any one ancestor is only 1 in 2,048.” That is, as with gin and tonic, if you keep mixing the drink with tonic, you eventually no longer taste the gin. Somehow, in spite of apparently understanding this inevitable dilution, Darwin still expected natural selection to work. For instance, in his example of wolves preying on deer, he concluded, “If any slight innate change of habit or of structure benefited an individual wolf, it would have the best chance of surviving and leaving progeny. Some of its young would probably inherit the same habits or structure, and by the repetition of this process, a new variety might be formed.” But the simple fact that this expectation was absolutely untenable under the assumption of a blending theory of heredity did not occur to Darwin. The inconsistency was first noted by the Scottish engineer Fleeming Jenkin.

Jenkin was a multitalented individual whose pursuits ranged from drawing portraits of passersby to designing undersea telegraph cables. His criticism of Darwin was fairly straightforward. Jenkin argued that natural selection would be totally ineffective in “selecting” a single variation (a rare novelty that arose by chance, which he referred to as a “sport”; today we would call it a mutation), because any such variation would be swamped and diluted by all the normal types in the population and obliterated entirely after a few generations.