A DNA molecule with a red spot illustrates the question, "What is random mutation?"

What exactly happens during random genetic mutations? What is random mutation, and how do these spontaneous changes affect living organisms?

Random mutation stands as a fundamental concept in evolutionary biology, representing unplanned changes in genetic material that can alter an organism’s characteristics. From Darwin’s early theories to modern scientific understanding, our knowledge of genetic mutations has evolved dramatically over time.

Keep reading to get Daniel Dennett’s explanation from Darwin’s Dangerous Idea of how these genetic changes shape life itself.

Random Mutation

What is random mutation? Dennett explains that random mutation is a series of unplanned, undirected changes in genetic material. These mutations occur spontaneously during DNA replication or as a result of environmental factors such as radiation or chemical exposure. Random mutations can lead to changes in the physical characteristics (known as the phenotype) of an organism, such as differences in appearance, structure, or the function of body parts.

Along with natural selection, random mutation is one of the two key steps of the evolutionary process theorized by Charles Darwin. According to Dennett, these changes are not guided by any intelligence or purpose; instead, they happen purely by chance.

Darwin and Pangenesis Theory

It’s important to note that, while Darwin accurately explained the results of evolution, his understanding of the mechanisms of random genetic mutation was limited because science had not yet discovered genes or DNA. As Siddartha Mukherjee writes in The Gene, Darwin (incorrectly) proposed small “particles” of inheritance produced by cells and carried in the blood, which he called gemmules. According to Mukherjee, Darwin theorized that streams of these particles from each parent would mingle in their offspring, thereby blending the parents’ traits. He called this theory pangenesis (meaning “originating from everything”) to illustrate that any given gemmule could come from anywhere in the body.

He also believed that, because any cell could produce gemmules, those gemmules would carry information about changes that cell had undergone—for instance, injuries or muscles made stronger through a lifetime of exercise. In other words, pangenesis theory relied in part on the inheritance of acquired characteristics, rather than purely genetic ones.   

Most Mutations Are Insignificant or Harmful

Dennett notes that most mutations don’t lead to improved features or enhanced survival capabilities. In fact, he writes, the vast majority of mutations either have no discernible impact at all or tend to corrupt or degrade features rather than improve them—resulting in malfunctions or abnormalities that can be detrimental to an organism’s survival chances. Dennett emphasizes that only a very small percentage of mutations result in beneficial changes that enhance an organism’s genetic fitness for survival and reproduction and therefore get passed on.

Types of Mutation

The abundance of disease-causing variants of genes stems from DNA’s role in coding for complex and highly specific proteins. Mutations often result in those proteins being made incorrectly (or not being made at all). Since proteins carry out thousands of different tasks within the body, those mutations can interfere with bodily functions in countless ways. 

Broadly speaking, there are three types of mutations:

A silent mutation has no effect; despite the mutation, the gene ends up coding for the same protein as before. It’s like replacing one word in a sentence with another word that means the same thing. For example, “I’m driving to the store” becomes “I’m going to the store.” Each sentence has the same meaning; likewise, silent mutations preserve the gene’s function. 

A missense mutation causes the gene to produce a different protein than usual. Proteins with missense mutations often carry out their tasks less effectively, if they can perform them at all. For example, in sickle-cell anemia, a change in the protein hemoglobin causes red blood cells to become deformed and rigid, making it more difficult for those cells to carry oxygen throughout the body. Again, imagine replacing one word in a sentence, but this time you replace it with something that changes the meaning—“I’m driving to the store” becomes “I’m dancing to the store.” Like a gene with a missense mutation, the revised sentence doesn’t serve its original purpose.

A nonsense mutation makes it so the gene’s instructions are cut off early, usually making the protein stunted and nonfunctional. For example, in cystic fibrosis, a missing or nonfunctional cell membrane protein prevents moisture from passing through and entering the lungs. As a result, mucus that would normally get cleared out of the lungs becomes too thick and sticky to expel. A nonsense mutation is like replacing a word with a period, so “I’m driving to the store” becomes just “I’m.” The incomplete sentence can’t convey its intended message, just as a nonsense mutation renders the protein too short to function properly. 
What Is Random Mutation? Daniel Dennett Explains

Elizabeth Whitworth

Elizabeth has a lifelong love of books. She devours nonfiction, especially in the areas of history, theology, and philosophy. A switch to audiobooks has kindled her enjoyment of well-narrated fiction, particularly Victorian and early 20th-century works. She appreciates idea-driven books—and a classic murder mystery now and then. Elizabeth has a blog and is writing a book about the beginning and the end of suffering.

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