Rise of the Animal Kingdom and Epigenetic Mechanisms of Evolution - Building the Most Complex Structure on Earth - page 270

with any degree of certainty the mechanisms that drove the unprecedented rapid evo-
lution of the Cambrian biota. Paleobiological and comparative biological techniques
have created a general picture of the dynamics of the Cambrian diversification, but it
can only indirectly, if at all, help us determine the driving forces of this unique event
in the evolution of animals.
However, it seems that some general biological principles may be a valuable
means of acquiring ample scientific insights into the mechanisms and processes that
drove the Cambrian explosion.
Other Insights into the Possible Role of the Centralized
Nervous System in the Cambrian Diversification
The history of the evolution of bilaterians is buried deep in the Cambrian, but extant
eumetazoans are “historical” structures. For two centuries, or about 150 years since
Haeckel, most biologists have continued to hold that the evolutionary history of
animals may be retrieved from individual development. Indeed, the evolution of
animals, essentially, is the visible result of the evolution of animal developmental
processes. Most evolutionary changes or novelties reflect specific changes in the
developmental pathways. Developmental changes and evolutionary changes are two
sides of the same coin. Commenting on Haeckel's biogenetic law, almost a century
ago, English zoologist Walter Garstang (1868-1949) pointed out:
Ontogeny does not recapitulate phylogeny, it creates it.
Garstang (1922)
In this sense, development runs the show of evolution. What controls development
controls evolution. So what controls development, itself?
I postulate that mechanisms controlling the development of morphological traits
during individual development are responsible for the evolution of these traits in
their Cambrian ancestors. This principle of phylogenetic actualism stems from
Haeckel's biogenetic law.
In my previous work ( Cabej, 2004, 2008, 2012 ) I developed and supported with
adequate empirical evidence, the hypothesis that the individual development in eumeta-
zoans takes place in two stages and is under a bigenerational control. During the first
stage, from the unicellular state (egg or zygote) until the phylotypic stage, development
takes place under epigenetic control of the parental cytoplasmic factors provided with
the gamete(s). At the onset of the phylotypic stage, the exhaustion of the parental epi-
genetic information coincides with formation of the operative CNS, which takes over
the continuing development until adulthood. It is the source of the epigenetic informa-
tion provided in the form of biochemical inducers that trigger signal cascades for cell
differentiation and tissue and organ growth. The evidence in support of the hypothesis
shows that “the nervous system has a central role in animal evolution” ( Jablonka, 2009 )