A new model of the Cambrian explosion

The existence of organs and apparatuses in an animal implies the existence of a body plan, and therefore even the most primitive animals (with the possible exception of sponges) had body plans. It is unlikely, however, that the very first animals could already use their body plans as deposits of information, i.e. as supracellular memories. We have seen that the embryonic development of many characters can be realised with two different strategies, a continuous mechanism (simpler) and a discontinuous one (more complex), and the simpler mechanism is also the one that comes first in the history of life. 

In the case of behaviour, for example, a totally instinctive modality is not only simpler but also more primitive than a behaviour which is dependent on some forms of learning. More generally, a strategy that 

It is likely, in other words, that the first animals had embryonic developments totally programmed by genes, and that only later did developmental strategies evolve that could also exploit the supracellular information of the body plan. This shift from a continuous (one-phased) development to a discontinuous (two-phased) one would have been a tranformation of enormous importance, and could well correspond to the Cambrian explosion. This is a new hypothesis, and it may be worthwhile to consider its predictions for what happened before, during and after the Cambrian explosion. 

The embryonic development of the very first animals was almost totally hard-wired, and this had two important implications. The first is that all embryonic stages were controlled by genes, including the phylotypic stage, and this means that the body plans were modifiable by genetic changes. This was the period in which old body plans could be transformed and new body plans could be invented. The second implication is that those animals were necessarily small and relatively simple, because there is a limit to the number of characters that can be directly controlled by genes. 

We have therefore a new model which can be summarised in this way the Cambrian explosion was the transition from a primitive type of development that was totally controlled by genes to a discontinuous type of embryonic development that could also use, from a certain point onwards, the supracellular information of the body plan. 

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