On May 4, 2014, at 9:24 PM, Richard Aiken <xxxxxx@gmail.com> wrote:

>
> "each mutation can arise independently, spread through the population by natural selection, and combine through sexual reproduction (or gene transfer in simpler organisms)."
>
> Doesn't this actually break natural selection, though? Organisms with currently-useless bits are less efficient than ones without them, so natural selection would not operate in favor of keeping an (only useful in the future after it meets its other half) mutation in the gene pool.

This is a very common misunderstanding.

Natural selection is not 100% efficient; nor do mutations disappear so rapidly. (otherwise we’d not have any of a rather large number of genetic diseases like cystic fibrosis.)

Natural selection doesn’t actually ‘select’ in the way you are reasoning.

Organisms pass on their genome whole, not piecemeal. A mutation that severely inhibits reproductive success will likely rapidly disappear. A mutation that enormously improves reproductive success will probably spread quickly. 99.999999% of mutations are neither.

Mutations that do not affect reproductive success don’t have any selective pressure at all, and so get passed along.

All of this is not taking into account environmental effects: gene regulation is very much affected by the environment, and mutations in the genes doing that can have enormous effects…IF certain environmental conditions are met. (all that ‘Junk DNA’ we were taught about in school back in the 60’s and 70’s…a lot of it’s actually regulatory genes used in development…how this bunch of cells turn into arms, that bunch legs, etc. Much of the rest is used in regulation of other gene expression.)

It’s not so clear cut and dried.

> It could still happen - humans have that pesky appendix, after all - but it wouldn't be *selected.*

That pesky ‘appendix’ has been found to have a role in the immune system. <http://www.news-medical.net/news/2007/10/08/30907.aspx>

> So we're back to random chemical junk (which doesn't do anything currently beneficial within an organism) randomly combining into something useful.

Sigh…you missed the point. Go back and re-read the example of the flagella, it’s the classical model of this process.

Here’s a good starting source: <http://www.amnh.org/exhibitions/past-exhibitions/darwin/evolution-today/how-does-natural-selection-work>

The whole exhibit will help answer questions.
--
Bruce Johnson
University of Arizona
College of Pharmacy
Information Technology Group

Institutions do not have opinions, merely customs