118 Evolution and the Fossil Record
evolutionary past and are adaptations to their developmental environment. Thus it is dan-
gerous to overextend the evolutionary implications of the stages in an embryo, but they are
useful guides nonetheless.
Creationists such as Jonathan Wells (2000), in their eternal effort to mislead the unini-
tiated and miss the forest for the trees, will crow about how the biogenetic law has been
discredited. But Haeckel’s overenthusiasm does not negate the careful embryological work
of von Baer that shows that many features of our past evolutionary stages are preserved in
our embryos. Wells, in particular, nags about how some of Haeckel’s original diagrams had
errors and oversimplifications, but this does not change the overall fact that the sequence
of all vertebrate embryos shows the same patterns in the early stages, and all of them go
through a fishlike stage with pharyngeal pouches (which become the gill slits in fishes and
amphibians) and a long fish-like tail, then some develop into fishes and amphibians and oth-
ers lose these features and develop into reptiles, birds, and mammals.
FIGURE 4.10. The evidence from embryology. As embryologist Karl Ernst von Baer pointed out in the 1830s,
long before Darwin published his ideas about evolution, all vertebrates start out with a very fishlike body
plan early in embryology, including the predecessors of gills and a long tail. As they develop, many lose their
fishlike features on their way to becoming reptiles, birds, and mammals. (From Romanes 1910)