Evolution

Evolutionary LOSS of Primal Eye &

The Cold to Warm-Blooded interface

Loss of the median eye seems to have occurred gradually among mammal-like reptiles, and quite suddenly among ancestral dinosaurs (Thecodonts). Fossil skulls suggest that ancient pineal systems included a median eye in reptiles directly ancestral to birds and mammals, as well as among proto-amphibians and fishes. The long history of this sensory organ, from the Ordovician fishes to present day lizards, attests to its importance as an adaptation.

In our cold-blooded ancestors, regulations of the storage and use of body-heat was critical to survival. Metabolic activity was dependent on sufficient availability of solar-energy and we can observe that present day reptiles only become active once they have warmed up their bodies sufficiently by basking or by exposure to warm surfaces on the ground. Thermo-regulation and the role of the pineal in transition from cold-blooded ectothermic to warm-blooded endothermic animals is an important theme, to which I shall return.

Recapitulation is wrong as pure theory, but is sometimes useful as an explanatory component within the Darwinian evolutionary paradigm. Haeckel’s theory puts the case that the stages of embryonic development retrace the whole evolution of that species. It is the case that embryos of different vertebrate species are indistinguishable at early stages of formation, but not true that they replicate the order of evolutionary changes, as Haeckel claimed. Human embryos during intrauterine development pass through stages from fish-like to reptilian, and then via non-primate mammalian to human primate. We have gill-(like) slits at one stage, and develop and lose a tail during our life as an embryo. The parietal foramen develops as though a median eye is to form and interestingly this opening is not completely lost during embryonic life but in humans takes about a year to close after birth. This is roughly the same time before a baby develops the idea of "self", i.e. can recognize its reflection in a mirror.

There is continual debate regards the extent to which recapitulation takes place and no general agreement whether it is necessary in some measure to explain Darwinian selection. Darwin himself believed that the theory was important. All I wish to establish for now is that the parietal opening has existed in each of us, during our early life, and that a physiological ‘memory’ of this stage of development might exist.

The nature of brain evolution is that as adaptations take place and new sensory capacities develop, new parts are added to the brain from the core outwards. The prefrontal lobes in humans are amongst the very latest stages of evolutionary development. However, the brain stem and old reptilian parts of the brain are retained and continue to function.