Mutations are changes in the genetic sequence, and they are a main cause of diversity among organisms. These changes occur at many different levels, and they can have widely differing consequences. In biological systems that are capable of reproduction, we must first focus on whether they are heritable; specifically, some mutations affect only the individual that carries them, while others affect all of the carrier organism's offspring, and further descendants. For mutations to affect an organism's descendants, they must: 1) occur in cells that produce the next generation, and 2) affect the hereditary material. Ultimately, the interplay between inherited mutations and environmental pressures generates diversity among species.*

Mutations affect the genetic code. The question is whether mutations cause the increase in new specified information in the genetic code which is required for the acquisition of new functional features which were not initially present in the life form's original genetic makeup, i.e. macroevolution.

According to evolutionist Masatoshi Nei mutation is the most important, driving force of evolution* Some evolutionary scientists say that mutations are essential raw materials for evolution. But the question is: what kind of evolution is really linked to mutations? Talk Origins is a pro-evolution club sponsored by powerful mainstream science organizations. On its website it states that most mutations are neither harmful nor helpful.* and the harmful mutations do not survive long, and the beneficial mutations survive much longer, so when you consider only surviving mutations, most are beneficial.*
Evolutionists like to believe that mutations cause macroevolution, the change from one unique life form to another, but in reality mutations are linked to microevolution, variety within a species. Evolutionists like to overstate the occurrence of beneficial mutations.

To date, most studies have suggested that most mutations with phenotypic effects tend to be deleterious to fitness. However, Shaw et al., studying the effect of mutations on fitness in Arabidopsis thaliana, now suggest that mutations can often have beneficial effects. These findings have been questioned by Keightley and Lynch.

In summary, the vast majority of mutations are deleterious. This is one of the most well-established principles of evolutionary genetics, supported by both molecular and quantitative-genetic data. This provides an explanation for many key genetic properties of natural and laboratory populations.

Deleterious mutations present a significant obstacle to adaptive evolution. Deleterious mutations can inhibit the spread of linked adaptive mutations through a population; conversely, adaptive substitutions can increase the frequency of linked deleterious mutations and even result in their fixation.

Under the neutral model, newly arising mutations fall into two major fitness classes: strongly deleterious and selectively neutral. The first class is well supported by mutation accumulation experiments and early DNA sequence comparisons and is shared among competing evolutionary models. The novel and controversial aspect of the neutral theory was the proposition that, among mutations that go to fixation, the vast majority are selectively neutral. Advantageous substitutions, although important in phenotypic evolution, are sufficiently rare at the molecular level that they need not be considered to adequately model the process.

The Neutral theory of molecular evolution states that...
most mutations are deleterious, but holds that because these are rapidly removed by natural selection, they do not make significant contributions to variation within and between species at the molecular level. A neutral mutation is one that does not affect an organism's ability to survive and reproduce. The neutral theory assumes that most mutations that are not deleterious are neutral rather than beneficial.*

Mutations are exceedingly harmful and the few that are neutral are not beneficial. Natural selection only prevents harmful mutations from surviving. The mutations that are neutral or beneficial cause phenotypic change, i.e. microevolution, i.e. variety within a species. Darwin's finches for example show that all kinds of beak sizes are possible within the genetic makeup of finches, but no beak ever changed into anything but a beak and all the finches never changed into anything but finches. Countless fruit fly mutations never resulted in anything but fruit flies, of which most were crippled.

Mutations result from errors during DNA replication or other types of damage to DNA... Mutations are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication. They can also be induced by the organism itself, by cellular processes such as hypermutation.*

Errors Are a Natural Part of DNA Replication ... Fixing Mistakes in DNA Replication ... When Replication Errors Become Mutations ... Even Low Mutation Rates Can Be Cause for Concern.*

It can of course not come as a surprise that mutations are harmful when we know what causes them. Causes and mechanisms of mutation are Errors in DNA replication... Errors in DNA repair... Environmental mutagen causes DNA damage that is not repaired correctly... Transposons and insertion sequences ... External Causes: Mutagenic agents that damage DNA such as chemical mutagens, physical mutagens or biological mutagens.* Mutations are errors which cause damage to the existing genetic code resulting in the opposite of evolution, namely degeneration.

DNA in cells suffers a wide range of damage... The importance of effective DNA repair systems is highlighted by the severe diseases affecting people with deficient repair systems... To cope with all these forms of damage, cells must be capable of several different types of DNA repair. DNA repair seldom involves simply undoing the change that caused the damage. Almost always a stretch of DNA containing the damaged nucleotide(s) is excised and the gap filled by resynthesis.

In most cases, the extensive network of DNA repair machinery that exists in the cell halts cell division before an incorrectly placed nucleotide is set in place and a mismatch is made in the complementary strand. However, if the repair machinery does not catch the mistake before the complementary strand is formed, the mutation is established in the cell. This mutation can then be inherited in daughter cells or in embryos.*

Due to the damaging effects that mutations have on genes, organisms are equipped with complex mechanisms such as DNA repair to prevent mutations from happening. This mechanism is preventive. This mechanism is not perfect and will inevitably miss harmful mutations. This further explains why life is not evolving, but rather devolving. See Entropy.

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