First off, great string of posts! It is rare to see a creationist that actually has the ability to admit that their argument might be flawed and who can think for themselves independent of the organized creationist's information stream.
So the causes of drift are, say, differences in breeding patterns within the population over time, or mutation?
Mutation always happens. You are not an exact copy of half your father and half your mother. Certain parts of your genetic makup are unique to you independent of your parents and that is a fact. The vast majority of these mutations do absolutly nothing. Some have a small negative or positive effect on your survivability depending on the environment you live in. Some that are unlucky enough to happen in an important piece of your genetic code may cause you to have a severe genetic defect. Luckly this is rare and due to decreased survivability these mutations are rarely passed on to offspring. Hence selection.
Mutation is the primary source of variability in a population. Selection ensures that bad mutations do not permeate the population and that good mutations will. Along with all the good and bad there are the neutal mutations that may or may not get passed on based on nothing more than random luck. Hence genetic drift.
Not sure I'm getting you. You mean scientists had noticed that the theory of evolution WOULD fail because of the overall tendency to reduction in variability from all the selective processes, and therefore had to suppose input from somewhere to balance out or overcome these processes?
Scientists do not suppose input in variability. Scientists did not invent the "concept of mutation". It is a fact that you are not a discrete representation of 1/2 of each of your parents genes. You have genetic variability that you did not recieve from your parents. Mutations happen and are observed.
In the bacteria monoculture, children of the original bacterium had genetic differences that they did not inherit from their parent. This genetic difference must have come from somewhere. Others on this site have tried to argue that the differences are a result of some kind of programmed mutation but have done so unsuccessfully. Either way, we know that changes in genetic variability in a new creature happen independently of its parent(s).
Because all the processes of evolution except immigration and mutation tend in that direction. Rate doesn't seem crucial if this is the overall tendency and these processes are operating as frequently as SEEMS to be understood to be the case. But I understand that the Hardy-Weinberg principle was formulated because of the observation of overall reduction in genetic diversity through all the processes of reduction, needing to account for the fact that in reality such drastic reduction in diversity doesn't occur as rapidly as would be expected if those were the only processes in operation.
And now I see the source of your main argument. You currently have an assertion that the combination of all the different types of selective pressures always constitutes a reduction in genetic variability. I would like to point out that this is an assertion and you must now provide evidence to show that is it more than such.
Any rate of mutation sufficient to be counterforce to the processes of reduction of variability seems to me to be a great rate.
Notice the "seems to me to be" portion of your quote. In order for your argument to be credible it needs to "actually be". If you can show that the rate that genetic variability being lost by selection is greater than the rate of genetic variability being introduced by mutation then you have a platform for your argument that evolution has limits.
Even if you can establish that the amount of mutation required to keep up with selection needs to be "great" in whatever metric you choose, you also need to show that such a "great" rate of mutation is detrimental. What is "great"?
Given that a not insignificant number of mutations happen each time an organism reproduces I am not convinced that selective pressures reduce the amount of genetic variability faster than mutations can put it back.
Yes, your bacterium. But still in my mind are the examples from the PBS program that called the process of selection of the poisonous newt and the antibiotic-resistant tuberculosis "mutation" while nevertheless ILLUSTRATING the process by diagrams showing that the adaptive trait was present in the beginning of the process. Surely that is not mutation, that is simply an already-present allelic variant. And such a case makes the whole question of mutation very iffy.
To clarify further about the bacteria experiment. If the population is decendent from a single genetic source then any trait that one individual has different from the source must have come from a mutation. If mutations could not produce genetic variability then there is no way that the child of a bacterium could attain a trait that was not also held by the parent.
In the particular experiment there were numerous bacteria that were genetically different enough from the original bacterium to be resistant to the anti-biotic. In fact, if I remember correctly, the mutation that conferred the resistance happened often, independent of heritability. In other words, it wasn't just one bacterium that gained the resistance and passed it on but rather many who independently gained the resistence off and on while the culture was not exposed to the anti-biotic. Someone else may be able to provide more details in the form of a source I hope.
I have trouble with the whole idea of mutation, a random input that follows no law but somehow manages to be a beneficial effect in some cases. The probabilities against anything that would increase survivability would seem to have to outstrip any rate of such random changes whatever but yes, I'm no mathematician and would rather keep away from rates and estimates. I don't think they are really necessary.
The random input is only beneficial because of selection. The best source of new information is a random number generator according to certain aspects of information theory.
In the case of the bacterium, the resistance to anti-biotics was only beneficial once the culture was actually exposed to teh anti-biotic. Before that the mutations were just part of the populations variability.
If you don't want to consider rates then you might want to reconstruct your argument because, when rigerously defined, your entire argument depends on rates. The "tendency" to reduce genetic variability is a rate. If your argument is that selection will "tend" to always reduce the genetic variability of a population despite mutation then you are already in the realm of rates!
Thanks,
By the way, for a fun second-term drinking game, chug a beer every time you hear the phrase, "...contentious but futile protest vote by democrats." By the time Jeb Bush is elected president you will be so wasted you wont even notice the war in Syria.
-- Jon Stewart, The Daily Show
™ Version 4.2
