Mutations are changes in the information contained in genetic material. For most of life, this means a change in the sequence of DNA, the hereditary material of life. An organism’s DNA affects how it looks, how it behaves, its physiology — all aspects of its life. So a change in an organism’s DNA can cause changes in all aspects of its life.
Mutations are random
Mutations can be beneficial, neutral, or harmful for the organism, but mutations do not “try” to supply what the organism “needs.” In this respect, mutations are random — whether a particular mutation happens or not is unrelated to how useful that mutation would be.
Not all mutations matter to evolution
Since all cells in our body contain DNA, there are lots of places for mutations to occur; however, not all mutations matter for evolution. Somatic mutations occur in non-reproductive cells and so won’t be passed on to offspring.
For example, the yellow color on half of a petal on this red tulip was caused by a somatic mutation. The seeds of the tulip do not carry the mutation. Cancer is also caused by somatic mutations that cause a particular cell lineage (e.g., in the breast or brain) to multiply out of control. Such mutations affect the individual carrying them but are not passed directly on to offspring.
The only mutations that matter for the evolution of life’s diversity are those that can be passed on to offspring. These occur in reproductive cells like eggs and sperm and are called germline mutations.
Read more about how mutations are random and the famous Lederberg experiment that demonstrated this. Or read more about how mutations factored into the history of evolutionary thought. Or dig into DNA and mutations in this primer.
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Reviewed and updated June, 2020.