The End of Evolution By Means of Natural Selection

Hi Faith, good to see you back in the ring - try not to let the mob wear you down First of all you find an existing dog that has as close to a desired characteristic as you can. Let's say you want a friendly breed, you find yourself a friendly dog. Then you find a friendly bitch that is as unrelated to the dog as possible. Then you interbreed them and hope that the things that make friendly dogs is passed onto the puppies from which the friendliest are selected and bred from etc.Breeds are often created by a breeders particular desires, or by a chance characteristic being discovered, preserved and then exaggerated (such as with minature or dwarf cats with very short legs).Then what tends to happen is that secondary traits might appear like a long tail. Characteristics are often linked like this, and not in obvious ways. For example: When scientists tried to tame foxes by breeding for friendliness, they found pretty 'doglike' coats forming (black and white spotty coats for example) even though they weren't specifically trying to create those coats. Turns out that the adrenaline biochemical pathways were being used by the melanin production side of things too. So by changing the genes that affect the pathway, they inadvertently messed around with the hair colours.After that - often the best way to find a dog with all the characteristics of the breed you like, is to look within the breed. More or less. I am not a dog breeder, or a geneticist - but this is my understanding of things, yes. A more complex question.
By nature of being a subset - it is almost certain to be lower in diversity than the whole. But you might mean 'does a dog breed have a lower diversity than a similarly sized random selection of dogs', and I think the answer is - maybe but not by an enormous amount.I suspect that if we only had the coding section of the genetic code to go on - it might take some time to identify a specific breed (barring computer intervention), so similar would it be to any other random dog. There is no platonic Beagle.There is only what people presently think are the characteristics required to be present or absent in order for a dog to qualify as being named a 'Beagle'.Nevertheless - there is a hell of a lot of genetics going on that don't affect the Beagle characteristics of an animal. A dog could have a mutated cytochrome c gene, which would be an increase in genetic diversity but the animal and its puppies would still qualify as Beagles and nobody sane would think they had lost any Beagleness to any extent by the change.Further - synonymous alleles could arise. Alleles act in the same way, but the genetic code for them is different. This would have no affect on said Beagle's nomenclatural status either.I do agree that genetic change in the alleles responsible for 'core Beagleness' - is likely to make something less Beagley than more Beagley. But it might make a Beagle more pleasing to the eye, and lead to a change in what people call a 'true Beagle'.But I disagree that genetic diversity within a breed is to be avoided. Breeder's tend to want as much genetic diversity in the Beagle population as possible while maintaining the traits they find pleasing. Darwin used domestic selection as one of the evidences for evolutionary forces and proposed that the natural effects of more offspring dying than reproducing would have a similar outcome to domestic selection but instead of being adapted to the needs of the farmer, the needs of whatever environmental factors are most key to their reproductive success. Natural selection is a requirement of adaptive evolution. Without it, adaptive evolution wouldn't happen. Just change basically. Speciation is the result of things changing over large expanses of space and time, at different rates and to adapt to slightly different needs.

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So two finches land on an island. There are 4 alleles max per gene. It's likely to be less. They reproduce until the island has 1,000 finches on it. Let's say no beak related mutations have occurred, and the beak alleles all do the same basic job. Further, let's say that natural selection of beaks only kicks in at 1,000 finches when a struggle for the resources of food comes in. Using their present beaks, the island can only support 1,000. Even if their beaks were just a little longer, the island could support 1,100.You seem to be suggesting that if some alleles tend to be in finches that have short beaks (eg., that allele is involved in making shorter beaks), then natural selection will lower the frequency of that allele - potentially to the point of eradication and the eradication of an allele is a loss of diversity therefore natural selection doesn't create diversity and if the 'engine of evolution' can't create diversity then evolution can't explain diversity even though it claims it can! Furthermore, since evolution requires subpopulations to occur which involves a loss of genetic diversity - and a requirement for no further genetic input from the parent population - evolution requires that evolution can't account for genetic diversity!But seriously, adaptive evolution (the kind of thing that explains eyes, hearts, legs etc) requires for their to be more that are born than survive to reproduce, for their to be variety from parent to offspring, for that variety to be heritable.The variety from parent to offspring is in the form of mutations. If adaptive evolution is occurring on our hypothetical island, then there may well be new beak creating alleles popping up. Most of them will either create maladaptive beaks or have no affect. But any mutation on any gene that is even indirectly linked to the beak has the potential to do something useful like create a slightly longer narrower beak. An island filled with finches with that kind of beak might be able to support 1,100 finches! This is adaptive evolution, and it requires variety in the form of heritable mutations.If this didn't occur, then you'd be right - evolution would simply be the dilution of a highly diverse parent population into ever more genetically sparse sub populations who just engage in recombination with one another. But it does occur, so you aren't right.Or, as Darwin said:

quote:

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Again, it may be asked, how is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species, which in most cases obviously differ from each other far more than do the varieties of the same species? How do those groups of species, which constitute what are called distinct genera, and which differ from each other more than do the species of the same genus, arise? All these results, as we shall more fully see in the next chapter, follow inevitably from the struggle for life. Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's power of selection. We have seen that man by selection can certainly produce great results, and can adapt organic beings to his own uses, through the accumulation of slight but useful variations, given to him by the hand of Nature. But Natural Selection, as we shall hereafter see, is a power incessantly ready for action, and is as immeasurably superior to man's feeble efforts, as the works of Nature are to those of Art.

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Some people think it's 'better' that we call them 'apples' rather than 'napples'. Some people think it is better to have a 'nick name' rather than an 'eke name'.Likewise some people prefer to sing

"Chorus.-For auld lang syne, my dear,
For auld lang syne.
We'll tak a cup o' kindness yet,
For the sake of auld lang syne. "

despite the fact that 'the sake of' is an error. Adding the extra syllables means there is one word per note which makes it easier and thus more communally pleasing, some people feel. It has become the 'standard' in may people's minds. But evolution isn't about getting a single correct answer. It's about finding a solution to a problem that's good enough to approximately optimise reproductive success. One of the results of this is that you don't need to start with the best solution, as long as your lineage remains in the top reproductively productive individuals. As long as you out-compete your peers it doesn't matter.Watch how some copying errors lead to better cars.You might not think it applies in genetics. But errors producing improvements, however counter-intuitive you find it, is a demonstrable fact.