Wednesday, 3 June 2009

5. Introductory concepts: brain forms - B.


Human molecular timescale. As shown on the left, our forebears are thought to have emerged from an RNA-based world into a DNA-based world about 4000 million years ago and current understanding of our journey to today may be usefully divided into 1000 million year chunks.

It is now very clear, on molecular and much other evidence, that all multicellular living things (animals including humans, and plants and fungi) evolved from the same or similar single cell organisms and that descendants of stages in this evolutionary process are with us today. Our understanding of our human place amongst living things has been assembled by studying modern versions as models of the evolutionary stages. As a result, we now know that we share a small fraction of our most basic molecular make-up (our genes) with bacteria and some viruses, about a third with daffodils, about half with worms, about three-quarters with dogs and almost all (about 98.5%) with our cousins, chimpanzees.

Of the many kinds of evidence underpinning the broad concept that all our natures are one, none is more cogent than the shared strategies we have evolved for our survival. For example, we must all consume food and we must all maintain an internal physical and chemical equilibrium in our bodies despite constant change in our surroundings. Our standard answer to the equilibrium problem has been the evolution of stimulus-response devices, beginning with molecular versions and proceeding via simple to complex nervous systems.

As shown on the right, there have been numerous instances of formal inversion during human neural evolution, and the diagram shows just six of these -- 3 molecular and 3 neural.

The point of the illustration is to emphasise that formal inversion appears to have been a consistent mechanism during our animal evolution, including the evolution of stimulus-to-response flexibility for survival in the natural world.

The next post will begin to look at these specific examples in more detail.

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