116 Evolution and the Fossil Record
Vestigial Structure and Other Imperfections
In chapter 2, we already alluded to the fact that organs that are remnants of past structures
but no longer serve a function were evidence against an intelligent designer. The list of such
vestigial organs (fig. 4.9) is overwhelming. They include not only the appendix, tonsils, and
tailbones of humans (none of which have a function now), but the tiny splint bones in the
feet of horses, which are remnants of the time when horses had three toes. When these bones
break, the horse is crippled for life. Whales and snakes both have tiny hips and thigh bones
buried deep in their bodies, with no function whatsoever. Why would they have these fea-
tures unless they evolved from ancestors that did have hind limbs? Any creationist attempt
to explain these remnants of ancient history falls into the same trap that Gosse did: a God
who would plant these vestiges of the past is a deceiver, tricking us by making it look like
life evolved.
A related issue is all the organ systems that are poorly or suboptimally designed, or
jury-rigged so they work just well enough for the organism to survive. We discussed these
in chapter 2 (especially the panda’s thumb and the fishing lures used by the anglerfish and
the clam Lampsilis). Once again, these organ systems do not look like they were intelligently
designed and only make sense if the organism must use whatever building blocks its ances-
tors provided.
Embryology
Even before Darwin, the studies of embryos began to provide important evidence for evo-
lution. In the 1830s, the great German embryologist Karl Ernst von Baer documented that
the embryos of all vertebrates show a common pattern (fig. 4.10). Whether they develop
into fish, amphibians, or humans, all vertebrate embryos start out with a long tail, well-
developed gill slits, and many other fishlike features. In adult fish, the tail and gills develop
further, but in humans, they are lost during further development. Von Baer was simply try-
ing to document how embryos developed, not to provide evidence of evolution, which had
not yet been proposed.
Darwin used this evidence in On the Origin of Species, and embryology soon devel-
oped into one of the growth fields of evolutionary biology. One of the foremost advocates
of evolution was the flamboyant German embryologist Ernst Haeckel. He not only pro-
moted Darwinism in Germany, but he went so far as to argue that we could see all details
of evolutionary history in embryos and reconstruct ancestors from embryonic stages of liv-
ing animals. His most famous slogan, the “biogenetic law,” was “Ontogeny recapitulates
phylogeny.” This is simply a fancy way of saying embryonic development (“ontogeny”)
repeats (“recapitulates”) evolutionary history (“phylogeny”). To the limited extent that von
Baer had shown 40 years earlier, this is true. But embryos also have many unique features
(yolk sac, allantois, amniotic membranes, umbilical cords) that have nothing to do with the
FIGURE 4.9. The evidence from vestigial organs. (A) Both whales and snakes retain tiny remnants of their
hind legs and hip bones in their bodies, although they are normally not visible externally, nor do they have
any function. These facts only make sense if whales and snakes had four-legged ancestors. Horses also retain
vestiges of their ancestral side toes, known as splint bones. (B) Close-up of the hip regions of a mounted fin
whale skeleton, showing the tiny vestigial hip bones and thigh bones. (Photo by the author) (C) In 1921, Roy
Chapman Andrews documented a specimen of a humpback whale that actually had atavistic hind limbs that
extended from its body. These are the bones of those hind limbs. (From Andrews 1921)