JTW's Evolutionary Origins - Author: Woese, Carl

On the Evolution of Cells

The Darwinian Threshold

The degree of connectedness of the componetry of the cell has profound evolutionary implications.

If a cell was simple and highly modular in organization, HGT [Horizontal Gene Transfer] would play a stronger role in its evolution than otherwise.

Indeed, were that organization simple and modular enough, all of the componetry of a cell could potentially be horizontally displaceable over time.

The organismal genealogical record would be ephemeral; no stable record could exist.

Suppose that the primitive ancestors of modern cells were of this nature.

That would mean that at its beginning, cellular evolution would have been mainly driven by HGT.

In its subsequent evolution a primitive cell of this type would become ever more complex, idiosycratically connected, and thereby increasingly refractory to horizontal gene acquisition, especially the more spectacular forms of it.

In other words, there would come a stage in the evolution of cellular organization where the organismal genealogical trace (recorded in common histories of the genes of an organism) goes from being completely ephemeral to being increasingly permanent.

This point in evolution, this transition, is appropriately call[ed] the "Darwinian Threshold".

On the far side of that Threshold "species" as we know them cannot exist.

Once it is crossed, however, speciation becomes possible.

The Darwinian Threshold truly represents the Origin of Species, in that it represents the origin of speciation as we know it.

• Woese, Carl R.
  • On the Evolution of Cells - *
  • Proceedings of the National Academy of Sciences, U.S.A.: Vol. 99, No. 13, pp. 8742-8747
  • June 25, 2002
  • [Pubmed]

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