6. The Heritages of the Chordate Phylum

6.6 Conclusion

To be or not to be is fundamental for atoms and molecules. Isotopes, isomers and enantiomorphs allow for a certain variability but, in general, a small change in an atomic or molecular structure provokes a radical and absolute change in properties. Burgeoning Life, up to the system of genetic transfer of information, also follows this rule of “all or none”: a modification of the genetic material results in annihilation of the living entity. If it survives, i.e. is mutated, the mutation follows the same rule of all or none: there is no gradation in the character transformed but a radical change. Hormones and nervous impulses function also on an “all or none” basis. A physiological process takes place when a certain concentration of a hormone is reached, a nervous impulse propagates along a neuron when a certain level of excitation is reached. Some hormones, however, modulate the response.

A brilliant achievement of the chordate phylum was the integration of the hormonal (chemical) and nervous (electrical) systems of communication and the refinement of the integrated system to such a point that a modulation of perception of stimuli and delivery of responses became possible. The genetic system of transfer of information was amended and improved by hormones and was almost totally bypassed by nervous structures that allowed memorization and intelligence. Instinctual behavior that demands immediate and complete satisfaction was superseded by rational behavior.

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