The Questions of Developmental Biology

To go from functional biology to evolutionary biology without development is like going from
displacement to acceleration without dealing with velocity.
4. Lack of genetic similarity in disparate organisms. We have come a long way from when
Ernst Mayr (1966) could state, concerning macroevolution: "Much that has been learned about
gene physiology makes it evident that the search for homologous genes is quite futile except in
very close relatives." Indeed, when one considers the Hox genes, the signal transduction cascades,
and the families of paracrine factors, adhesion molecules, and transcription factors, the opposite
has been seen to be the case. Adult organisms may have dissimilar structures, but the genes
instructing the formation of these structures are extremely similar.
The population genetics model was formulated to explain natural selection. It is based on
gene differences in adults competing for reproductive advantage. The developmental genetics
model is formulated to account for phylogeny evolution above the species level. It is based on
the similarities in regulatory genes that are active in embryos and larvae. We are still approaching
evolution in the two ways that Darwin recognized. One can emphasize the similarities or the
differences.
When the Modern Synthesis was formulated, developmental biology (and developmental
genetics) were not even sciences. Embryology was left out of the Modern Synthesis, as most
evolutionary biologists and geneticists felt it had nothing to contribute. However, we know now
that it does. The developmental genetics approach to evolution concerns more the arrival of the
fittest than the survival of the fittest.
Even critics of the Modern Synthesis (including Goldschmidt and Gould) agree that
macroevolutionary change is predicated upon mutation and recombination. However, these
macroevolutionary changes are in developmental regulatory genes, not the usual genes for
enzymes and structural proteins; and these changes occur in embryos and larvae, not in adults
competing for reproductive success (see Waddington 1953; Gilbert 1998).
Developmental biology brings to evolutionary biology, first, a new understanding about
the relationships between genotypes and phenotypes, and second, a new understanding about the
close genetic relationships between organisms as diverse as flies and frogs. In doing so,
developmental biology complements the population genetics approach to evolutionary biology.
It also highlights new questions. For instance, there can now be a population genetic approach to
the regulatory genes (see Arthur 1997; Macdonald and Goldstein 1999; Zeng et al. 1999).
One can also look at how paracrine factors, signal transduction pathways, and transcription
factors have changed during the evolution of various phyla. Evolutionary developmental biology
can also provide answers to classic evolutionary genetics questions such as these posed by
mimicry and industrial melanism. The genes involved in these processes are being identified so
the mechanisms of these phenomena can be explained (Koch et al. 1998; Brakefield 1998).
To explain evolution, both the population genetics and the developmental genetics accounts are
required.
Leaving developmental biology out of the population genetics model of evolution has left
evolutionary biology open to attacks by creationists. According to Behe (1996), population
genetics cannot explain the origin of structures such as the eye, so Darwinism is false.*
How could such a complicated structure have emerged by a collection of chance mutations?
If a mutation caused a change in the lens, how could it be compensated for by changes in the
retina? Mutations would serve only to destroy complex organs, not create them.