Evolution

I just came across an essay by James Shapiro on new and unsettled questions in evolution. The article is written for the educated lay reader, so right about my level of sophistication in biology. There is a lot of interesting ferment in this area at present. A good part of my blog reading these days is on recent human evolution, and the interactions of heredity and culture.

I have a blog post waiting in the wings about paternal age and genetic load, which I thought of when I read this passage in Shapiro's essay:

(2) Cellular Repair Capabilities. First, then, all cells from bacteria to man possess a truly
astonishing array of repair systems which serve to remove accidental and stochastic sources of mutation. Multiple levels of proofreading mechanisms recognize and remove errors that
inevitably occur during DNA replication. These proofreading systems are capable of
distinguishing between newly synthesized and parental strands of the DNA double helix, so
they operate efficiently to rectify rather than fix the results of accidental misincorporations of
the wrong nucleotide. Other systems scan non-replicating DNA for chemical changes that
could lead to miscoding and remove modified nucleotides, while additional functions monitor
the pools of precursors and remove potentially mutagenic contaminants. In anticipation of
chemical and physical insults to the genome, such as alkylating agents and ultraviolet radiation, additional repair systems are encoded in the genome and can be induced to correct damage when it occurs.


It has been a surprise to learn how thoroughly cells protect themselves against precisely the kinds of accidental genetic change that, according to conventional theory, are the sources of evolutionary variability. By virtue of their proofreading and repair systems, living cells are not passive victims of the random forces of chemistry and physics. They devote large resources to suppressing random genetic variation and have the capacity to set the level of background localized mutability by adjusting the activity of their repair systems.

And in the blog post that sent me to to Shapiro, here is a good one from my patron, Thomas Aquinas:

Species, also, that are new, if any such appear, existed beforehand in various active powers; so that animals, and perhaps even new species of animals, are produced by putrefaction by the power which the stars and elements received at the beginning.

-- Summa theologica, Part I Q73 A1 reply3

An Aristotelian evolution would look not only to external forces, but to the abilities of living things to create change within themselves.