How do so many new variations arise if mutations are very rare?
Mutation is the ultimate source of variation upon which natural selection acts, and that's how we have so many different species. But since mutations are extremely rare, because most of the time DNA is duplicated accurately, how did we end up with an amazing variety of organisms?
First, mutations are not that rare. Mutations occur all the time, and while it's true that most mutations are not beneficial, some of them are, and some are neutral. Some harmful mutations are even able to get passed along, because they essentially hitch a ride with the rest of the genome and despite causing some problems, they do not prevent the individual from reproducing. Second, there have been billions of years of evolution for variations to occur and accumulate. Over a very long time period, rare or statistically unlikely events will occur many times. Third, genes are not the full story when it comes to phenotype (traits). The environment also has a huge effect, and gene expression patterns can be changed without changing the gene itself. If you take identical twins, with the same genome, and starve one while the other is fully nourished, they will most likely have a different weight and there may even be differences in height and intelligence when they reach adulthood.
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