Re: Shall we get rid of our junk?

On Fri, 16 Dec 2005 16:51:23 -0500 (EST),
Perplexed in Peoria <jimmenegay@xxxxxxxxxxxxx> wrote:

[snip]

> It seems that there are three selective forces that must be
> considered:
>
> 1. Presumably there is a small negative fitness effect on
> individuals who carry a lot of junk because of the metabolic
> cost of replicating the junk.

This is probably correct but the effect must be very small in
those species that can tolerate large amounts of junk DNA.

> 2. In a sexual population (and the question is meaningless if
> the population is not sexual) there is presumably a negative
> fitness effect on any individual who carries a different
> pattern of junk than do his potential mates. This is because
> the chromosomes will not be quite so homologous and this will
> interfere with recombination and perhaps even with mitotic
> segregation.

The differences between individual chromosomes are insignificant.

[snip]

> 3. Finally we are presuming that beneficial mutations arise more
> frequently in high-junk individuals.

There is no evidence to support this assumption and no obvious
reason why it has to be invoked, other than looking for
adaptationist explanations of junk DNA. If you believe that
nature is "designed" by natural selection then junk DNA is a big
problem. If you believe that accident plays a large role in the
history of life then junk DNA is confirmation.

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.)



Larry Moran


.

Relevant Pages

  • Re: Junk DNA: A hypothesis
    ... >> mutations on the remote chance that some of them will be beneficial ... On the other hand, negative selection, coupled to a quantum-mechanically ... In this case you suggest that junk DNA has to be ... > aggravated by adding arrogance (not the least AEVASIVE arrogance) ...
    (sci.bio.evolution)
  • Re: Cold water on micro-RNAs
    ... There is a cost for replicating the genome, ... However your prediction that mutation and selection would quickly dispose of junk DNA is not solidly based. ... In eukaryotes the cost of DNA replication is a relatively small part of the cell's energy and materials budget, compared to bacteria where the cost of DNA replication is significant and junk DNA is essentially absent. ...
    (talk.origins)
  • Re: Junk DNA: A hypothesis
    ... Tim Tyler wrote: ... the evidence suggests that junk DNA is really junk? ... then it has a very low chance of becoming fixed by natural selection. ... > selective forces can have dramatic long-term effects. ...
    (sci.bio.evolution)
  • Re: Junk DNA: A hypothesis
    ... > hypothesis (that junk DNA allows a less destructive shuffle to take place). ... Why would stretching out a gene by inserting introns be an adaptation? ... I'm not against any form of group selection and I'm quite well aware ... >> If your speculation is correct then there should have been much less ...
    (sci.bio.evolution)
  • Re: Junk DNA: A hypothesis
    ... But once again you are postulating selection for some future ... >> individual know that it needs to store excess DNA in its genome because ... Junk DNA could just be junk that's there by accident. ... then it will be the case that the organisms we see today ...
    (sci.bio.evolution)