Causal Enigma of the Evolution of Animal Morphology
Which came first: the nervous system or the increased animal morphology?
More than half billion years ago, during an evolutionarily very short period of time, an extremely rapid diversification of animal morphology took place that led to formation of all the extant and more extinct phyla that, for this reason, biologists call it Cambrian explosion. The New Synthesis has been unable to rationally explain the driving forces of the phenomenon, thus facilitating creationist attacks on the theory of evolution.
During the Cambrian explosion, more than half a billion years ago, the eumetazoans, i.e. the early branch of metazoans that evolved nervous system succeeded in evolving the vast majority of animal phyla and species populating the earth, while the branches that failed to develop a nervous system (placozoans and sponges) remained “dead ends” of Animal Kingdom. The latter evolution also shows that a correlation exists between the degree of the complexity of the nervous system and the degree of morphological complexity of metazoans. While the correlation might suggest a causal relationship between the nervous system and the amimal morphology, it is not easy to discriminate between the cause and effect. Indeed the discrimination of cause and effects is often difficult, especially in cases like this, when the both the presumed causes and effects appear at the same time.
Anyway how could we safely determine whether the evolution of the nervous system is the cause of the increased morphological complexity in metazoans or the reverse is true?
All the evolutionary changes in phenotypy occur during the individual development, This fact allows to predict that if the nervous system is the cause of the evolution of animal morphology then the nervous system, but not other organ systems (excretory, digestive, circulatory, respiratory, etc.), must be crucially involved in the development of animal morphology and morphogenesis.
Adequate and even ample empirical evidence shows that the nervous system uniquely is involved in the development of all organ systems during the individual development (See chapter 6 of Epigenetic Principles of Evolution for the relevant evidence) a major fact that indicates the critical role played by the differentiation of the neuron and evolution of the nervous system in evolution and taxonomic and morphological diversification of animals..