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The “developmental hourglass” doesn’t actually need to be true

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It’s too cool a concept for accuracy to matter. Further to “Remember the ‘developmental hourglass’? Well, not so fast,Jonathan Wells writes to point out that vertebrate embryos more closely resemble each on another than do their adult forms only if one carefully cherry-picks the desired stages, which are long after the beginning of development. In Zombie Science, he writes,

In 2008, University of Chicago historian Robert Richards published a book defending Haeckel against charges of fraud. According to Richards, Haeckel’s drawings were no less accurate than those of his contemporaries, including the people who criticized him. 37 Cambridge historian Nick Hopwood also defended Haeckel against the fraud charge in a 2015 book that included several pages criticizing Icons of Evolution as a creationist “primer for textbook activism.” 38

The real issue, however, is not whether Haeckel deliberately committed fraud. The real issue is that Haeckel’s drawings omitted half of the evidence—the half that doesn’t fit Darwin’s claim that embryos are most similar in their early stages. By the logic of Darwin’s argument, the earliest stages should be the most similar, but vertebrate embryos actually start out looking very different from each other, then they converge somewhat in appearance midway through development (Haeckel’s “first” stage) before diverging to their adult forms. 39 Biologist Rudolf Raff has called this pattern the “developmental hourglass.” 40 Haeckel helped Darwin by simply omitting the top half of the hourglass.

When Jerry Coyne reviewed Icons of Evolution in 2001, he criticized the book for failing to recognize that “embryos of different vertebrates tend to resemble one another in early stages, but diverge as development proceeds, with more closely related species diverging less widely,” thus providing “copious evidence for evolution.” Yet Coyne knew that vertebrate embryos are not most similar in their early stages. Indeed, in the same review he acknowledged that “the earliest vertebrate embryos (mere balls of cells) are often less similar to one another than they are at subsequent stages.” But he brushed this aside. For Coyne, evolution must be true, whether early embryos are similar or not. 41 Coyne followed this with a 2009 book titled Why Evolution Is True, which contained the following: “Each vertebrate undergoes development in a series of stages, and the sequence of those stages happens to follow the evolutionary sequence of its ancestors.” Thus “all vertebrates begin development looking like embryonic fish because we all descended from a fishlike ancestor.” 42

So much for the evidence.
— — –
[37] Robert J. Richards, The Tragic Sense of Life: Ernst Haeckel and the Struggle over
Evolutionary Thought (Chicago: University of Chicago Press, 2008).
[38] Nick Hopwood, Haeckel’s Embryos: Images, Evolution, and Fraud (Chicago:
University of Chicago Press, 2015).
[39] Jonathan Wells, Icons of Evolution (Washington, DC: Regnery Publishing, 2000),
[40] Rudolf A. Raff, The Shape of Life: Genes, Development, and the Evolution of
Animal Form (Chicago: The University of Chicago Press, 1996), 197.
[41] Jerry A. Coyne, “Creationism by stealth,” Nature 410 (2001): 745–746.
[42] Jerry A. Coyne, Why Evolution Is True (New York: Viking Penguin, 2009), 77–79.

See also: Remember the “developmental hourglass”? Well, not so fast. “Organizational checkpoints” as a substitute? Sure, but that is design, not Darwin.


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