Re: Shall we get rid of our junk?


"Larry Moran" <lamoran@xxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:do24k2$4eu$1@xxxxxxxxxxxxxxxxxxxxxx
[Is there a selectionist explanation for "junk DNA"]

> Most of the current "controversy" comes from hard-core
> adaptationists. They just can't accept the idea that a large amount
> of evolution may not be due to natural selection. It goes against
> everything that they stand for so they make up just-so stories
> to explain the selective advantage of junk DNA. (Or, they claim
> that there's some secret selective advantage that we haven't yet
> discovered after 35 years of looking.)

I happen to be rereading Gould's brick-like book "The Structure
of Evolutionary Theory" and I chanced to open the book to the
section where Gould discusses this topic. Gould, of course,
considers junk DNA to be a spandrel, and a potential exaptation.
But he is orthodox enough to discount any selectionist explanation
for something which might prove useful in the future - even an
explanation utilizing his beloved species-level of selection.

However, in view of their potential exaptational value, Gould
at one time argued that pseudo-genes and such should not be
given the disparaging descriptor of "junk". However, he was
cured of this opinion after reading this delicious passage
by Sydney Brenner (in an article with an equally delicious title):

Some years ago I noticed that there are two kinds of rubbish
in the world and that most languages have different words to
distinguish them. There is the rubbish we keep, which is junk,
and the rubbish we throw away, which is garbage. The excess
DNA in our genomes is junk, and it is there because it is
harmless, as well as being useless, and because the molecular
processes generating extra DNA outpace those getting rid of it.
Were the extra DNA to become disadvantageous, it would become
subject to selection, just as junk that takes up too much space,
or is beginning to smell, is instantly converted to garbage.

Refuge of Spandrels
Sydney Brenner
Current Biology 1999, p669


.

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