Fruit flies have a short lifespan and replicate fast. Therefore they are good for experimentation with mutations. They are often mentioned by evolutionists in support of their belief in macroevolution. But do the countless experiments with fruit flies support macroevolution or microevolution?

Perhaps, scientists speculated, evolution took place as genes were altered. DeVries claimed that if a gene changed - if it "mutated" - it would create a new species in a single jump.
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Evolutionists like Hugo De Vries believed, based on their preconceived belief, that mutations would account for macroevolution.

Morgan bred fruit flies by the thousands, and his team tried to create mutant flies with x-rays, acids, and other toxic substances. Finally, in one unaltered lineage of flies, the researchers found a surprise. Every single fly in that line had been born with red eyes, until one day a fly emerged from its pupa with white eyes. Something had spontaneously changed in the white-eyed fly. ... Here was a mutation, but one that didn't fit DeVries's definition. DeVries thought that mutations created new species, but the fly that had acquired the white-eyed mutation remained a member of the same species. It could still mate with other fruit flies, and its gene could be passed down to later generations in proper Mendelian fashion.
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Thomas Hunt Morgan was a saltationist who hoped to demonstrate that a new species could be created in the lab by mutation alone. Instead, his work between 1910 and 1915 reconfirmed Mendelian genetics and provided solid experimental evidence linking it to chromosomal inheritance. He found that mutations did not account for macroevolution. He stated...

It is, of course, hardly to be expected that any random change in as complex a mechanism as an insect would improve the mechanism, and as a matter of fact it is doubtful whether any of the mutant types so far discovered are better adapted to those conditions to which a fly of this structure and habits is already adjusted. ... Evolution from this point of view has consisted largely in introducing new factors that influence characters already present in the animal or plant. ... In the breeding work with Drosophila we are dealing with artificial and unnatural conditions.
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Morgan's work demonstrated that most mutations had relatively small effects, such as a phenotypic change like eye color, and that rather than creating a new species in a single step, mutations served to increase variation within the existing population. Mutations are responsible for microevolution only. They don't create new specified information which is required for macroevolution. Besides that, all experiments required input of intelligence.

According to pro-evolution mainstream science organization NCSE The importance of the four-winged fruit fly is that it demonstrated that a few mutations in a single gene were able to transform an entire structure. * Evolutionists in general like to use the example of the four-winged fruit fly in support of their belief in macroevolution.

The neo-Darwinian scenario says that new structures are produced by natural selection acting upon purely undirected and random mutations. Yet, the mutants that produce four-winged fruit flies survive only in a carefully controlled environment and only when skilled researchers meticulously guide their subjects through one non-functional stage after another. This carefully controlled experiment does not tell us much about what undirected mutations can produce in the wild.
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But a four-winged fruit fly merely confirms that mutations do not cause new specified information in the genetic code, not even when all the clever evolutionary scientits perform them. In this case they simply copied pre-existing genetic code for wings. The extra wings were harmful because they made the fruit flies into cripples resulting in premature death, to be weeded out by natural selection. These crippled flies would never survive in nature, that's probably why we won't see any.

The genetic mistake did not produce a new complex structure. It just made an existing complex structure appear in a place where it would not work. We want to see a Hox gene make functional legs or wings appear on a worm. Is that a "frustrating request" or "an unreasonable burden"? What makes it unreasonable? It is unreasonable because everybody knows it can't possibly happen. But, for the theory of evolution to be true, it has to happen often. Reptiles had to grow breasts to become mammals, didn't they? Every internal organ of every living creature is a complex structure that had to be produced by a genetic mistake, if the theory of evolution is true.
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Of course this crucial point was already proven by Thomas Hunt Morgan in the early 1900s. Today nothing has changed in this regard.

Scientists have bombarded fruit flies with X-rays to try to get them to mutate, and it works. They get mutant fruit flies without wings, fruit flies without eyes, and lots of fruit flies that die quickly. But they have never produced a dragonfly or a butterfly. All they get are fruit flies with birth defects.
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It is a striking, but not much mentioned fact that, though geneticists have been breeding fruit-flies for sixty years or more in labs all around the world - flies which produce a new generation every eleven days - they have never yet seen the emergence of a new species or even a new enzyme.
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Today fruit fly fossils from the Eocene Period are sold which are around 55 to 45 million years old * The fact that fruit flies have simply not changed in 50 million years is hard evidence for macroevolution not taking place.

Why do certain body shape and size relationships remain consistent over millions of years?
"Our results suggest that these traits can evolve, but changing these relationships creates deleterious side effects for the organism. Therefore, evolution through natural selection will be strongly constrained, at least on shorter timescales of less than one million years," the researchers said.
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It's a simple fact that mutations are harmful and they are either repaired by means of DNA repair mechanism, they're deleted by natural selection, or they survive and cause degeneration. It's a hardcore fruit fly fact that in at least 50 million years no fruit fly has ever changed into anything but a fruit fly. The fossil record clearly supports the idea that macroevolution never took place.