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Author Topic:   Disabling Bacterial Resistance
Sylas
Member (Idle past 4500 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 46 of 60 (217229)
06-15-2005 5:06 PM
Reply to: Message 44 by mike the wiz
06-15-2005 3:26 PM


Re: Shraff, talk to me
However, why would it be selected? If it is just beneficial, I fail to see how NS could select it. I only see NS working when it has no choice. Example; Some plants with short roots can survive, but so can longer roots. Longer roots are beneficial so are selected, yet the short roots survive too? Isn't that just no change in the gene pool?

No. The measure used for gene pools is a frequency distribution. A change in the relative frequency of alleles is still evolution.

Here is a quick very basic evolution 101, defining a few important terms.

gene A gene is a particular bit of DNA at a particular location in the genome, with some functional role (usually coding for a protein). The unit of heredity.

allele A specific sequence of DNA for a gene. There can be a number of alleles for a gene in a population, and each individual has two alleles for every gene (one from each parent). In a population of organisms, there is a frequency distribution for alleles indicating how common each allele is within the population.

mutation A change in DNA sequence during replication. New alleles for a gene can arise through mutation.

genetic drift The frequency of alleles changes over time depending on how many instances happen to carry over into the next generation. Often the different alleles don't make any difference to an organism, but the frequencies will still go up or down just by the happenstance. This is called drift.

selection The number of surviving offspring for an organism in the next generation depends on all kinds of things. But sometimes having one allele or another can make a small change in the probable numbers of surviving offspring. This is called selection. Positive selection is when a certain allele increases the average expectation for numbers of surviving offspring; and negative selection is when the average expectation is reduced. This depends also on the environment, of course. The same alleles can be positively selected in one environment and negatively selected in another.

fitness The success of an individual, or of an allele, as measured by its probable frequency in successive generations. Alleles under positive selection are said to have increased fitness.

fixation Fixation is when the frequency for an allele reaches 100%. This can occur by drift, or by selection.

evolution The formal definition of evolution is often given as "change in the distributions of alleles in a population over time". Mutation, drift, and selection are all processes which impact the distributions of alleles; and hence they are mechanisms of evolution.

Now let's return to the length of roots. Typically, root length is affected by many different genes and many different alleles. There is no one gene for root length. However, if having longer roots gives an increased expectation for numbers of surviving offspring in the next generation, then this means a positive selective pressure on alleles which are positively correlated with longer roots; and negative selection for alleles that tend to lead to shorter roots.

Under this circumstance, the probability of fixation for new alleles tending to increase root length is raised; and the probability of fixation for new alleles tending to decrease root length is lowered.

Over time, the average root length of the population will increase. Looking at isolated individuals, you will still be able to find ones with short roots that prosper, but they will tend to be a bit less common. Over many generations, the mean root length will increase, and with strong selection or very long periods of time you will get to a point where you no longer find any plants with roots as short as the average length from an earlier time.

This is really basic. Selection can work on tiny changes in probability; it is simply false to say that selection only works when there is no chance at all for something with short roots to survive.

Mike; this is something of a deal-breaker for you. I've tried to set out the matter as clearly as a can in a single post, and I am happy to answer questions; but only if there seems to be some point in doing so. The basic meaning of these terms is not a point for debate. You don't get to invent new meanings for terms, and the phenomena of selection, drift, mutation, fixation, and so on are all directly observed.

Selection is a fairly simple concept, and it can be measured. There is no need for a selected allele to be essential for survival. You are trivially wrong to insist on this point, and you've been refuted on this in the thread many times. The only question at this point is whether or not you are capable of learning something.

When you solicited feedback in another thread, you got rather angry at my answers. I'm not surprised at that; I spoke strongly. It's not that I'm irritated with you. It's that over time I've come to the conclusion that it is a waste of time trying to explain such things.

You'll show I'm wrong when you can stop this childish nonsense about being "irrefutable" and show some capacity for actually learning something and grasping the points being explained.

Cheers -- Sylas


This message is a reply to:
 Message 44 by mike the wiz, posted 06-15-2005 3:26 PM mike the wiz has replied

Replies to this message:
 Message 48 by mike the wiz, posted 06-15-2005 7:36 PM Sylas has replied

  
Sylas
Member (Idle past 4500 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 49 of 60 (217266)
06-15-2005 8:23 PM
Reply to: Message 48 by mike the wiz
06-15-2005 7:36 PM


Re: Sylas, is mikey here to learn or refute?
I know that the vast accumulation of ToE information might work hypothetically, but then it has to. I still think my logic makes sense.

It doesn't. Your argument has been a trivial false dichotomy from the start. You have insisted that there is a necessity for selection to be all or nothing, and that if any individual survives with a particular feature, this means there can't be selection against it.

You've done this repeatedly in the thread; but it is wrong. Most creationists recognize it is wrong. Most creationists recognize "microevolution", including the effects of selection to bring about changes in form over time. It is not hypothetical at all, but confirmed in countless studies. Selection really does apply for features that an organism does not need to survive.

What selection requires is simply differential reproductive success. Organisms can live and reproduce and flourish without the selected characteristic; but those that flourish a bit better will, over time, displace the less well adapted form. If the selective pressures remain fixed indefinitely, then the less well adapted form is eventually removed altogether from the gene pool. Not because they could not survive, but because over time their proportion of the population dropped until it hit zero.

Your argument is If slower ones are eventually weeded out, then it seems faster ones were needed, because slower ones didn't survive them. You've not defended that syllogism. It's false.

The slower ones do survive and reproduce. They just do it a bit less effectively than the faster ones, and so as faster ones arise they tend to replace slower ones. If, as an experiment, you artifically killed off the faster ones, the slower ones would continue to live. In fact, you'd become part of a different environment and change the selective pressures.

How the plague do you think animal husbandry and breeding programs work? The farmer sets up an envionment with positive selection for the traits she prefers.

At this point Mike, you are being obtuse and confirming all the remarks I made in the other thread that you apparently found so baseless.

This is pointless; and it's not because you are irrefutable. It is because you are irrational. You purport to be defending a biblical world view, but in the end you only end up turning your back on the very creation you believe God made.

Goodbye -- Sylas


This message is a reply to:
 Message 48 by mike the wiz, posted 06-15-2005 7:36 PM mike the wiz has taken no action

  
Sylas
Member (Idle past 4500 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 59 of 60 (217760)
06-17-2005 7:44 PM
Reply to: Message 54 by mike the wiz
06-17-2005 11:44 AM


Now surely NS would select that which is needed to exist. Even a rudimentary system would be irreducabley complex IMO.

Ah! So that is what this is about. This is worth emphasizing, so I'm back for another comment...

No, natural selection does not select what is needed to exist.

You cannot get new changes arising that are "needed to exist", since the ancestor had to exist already. And changes that remove what are needed to exist are fatal. That could be thought of as a kind of selection; but only in a crude and uninteresting way.

Selection and evolution actually work on variants, both of which are able to exist but which may out compete each other in different circumstances. The key phease is differential reproductive success.

The examples Mike has raised include such things as running speed, and length of roots, and so on. These are not "needed to exist" in the absolute sense intended here.

This is the basis of the false dichotomy. Mike has been suggesting that selection of a feature can only mean it is "needed to exist", and that continuing existence of some earlier feature means that the new feature is not needed to exist. Therefore no evolution. See, for example, Message 22.

The notion of "needed to exist" is also fraught with problems; since what is needed to exist changes over time as environment and as the form of an organism changes. Organs that are needed in one organism cannot merely be assumed essential in all its ancestors.

Cheers -- Sylas


This message is a reply to:
 Message 54 by mike the wiz, posted 06-17-2005 11:44 AM mike the wiz has taken no action

  
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