The Four Key Statements

1. Evolution by natural selection is progressive, it makes individuals ‘better’.

2. Natural selection acts on individuals but it is populations that change with time.

3. Natural selection does not cause genetic changes in individuals.

4. Natural selection acts on phenotype.

Let’s analyze each statement in the context of antibiotic resistance and natural selection.

1. Evolution by natural selection is progressive, it makes individuals ‘better’.

This statement is NOT true. Evolution by natural selection is not inherently progressive, nor does it make individuals universally “better.” Rather, natural selection favors traits that are advantageous in a specific environment at a specific time. For example, antibiotic resistance makes bacteria more likely to survive in the presence of antibiotics, but these same resistant bacteria may be less fit in environments without antibiotics. There is no universal direction or goal to natural selection; it does not strive for perfection or improvement, only for better adaptation to current conditions.

2. Natural selection acts on individuals but it is populations that change with time.

This statement is true. Natural selection operates by favoring individuals with advantageous traits—such as antibiotic resistance—allowing them to survive and reproduce more successfully than others. However, the genetic composition of individuals does not change during their lifetime. Instead, it is the population as a whole that evolves over generations, as the frequency of advantageous traits increases.

3. Natural selection does not cause genetic changes in individuals.

This statement is true. Natural selection does not induce genetic changes within an individual; rather, genetic changes (mutations) occur randomly. Natural selection then acts on these pre-existing variations, favoring individuals whose genetic makeup confers a survival advantage in a given environment. For instance, a mutation conferring antibiotic resistance may arise randomly in a bacterium, and if antibiotics are present, this bacterium is more likely to survive and reproduce, passing on the resistance allele.

4. Natural selection acts on phenotype.

This statement is true. Natural selection acts on the observable characteristics (phenotype) of organisms, not directly on their genes. In the case of antibiotic resistance, the phenotype is the bacterium’s ability to survive antibiotic treatment. The underlying genetic mutation is only favored because it produces a phenotype that increases survival and reproductive success in the presence of antibiotics.

Why the Misconception Exists

The idea that evolution is progressive and always makes organisms “better” is a common misunderstanding. In reality, natural selection is context-dependent: what is advantageous in one environment may be disadvantageous in another. For example, antibiotic resistance is beneficial to bacteria in environments with antibiotics, but may carry a cost in antibiotic-free environments, such as slower growth rates or higher energy expenditure.

The Real Lessons from Antibiotic Resistance

• Random Mutations: Antibiotic resistance often arises from random genetic mutations, not as a direct response to antibiotic exposure.

• Selection Pressure: The use of antibiotics creates a selection pressure that favors resistant bacteria, allowing them to survive and reproduce while susceptible bacteria die off.

• Population Change: Over time, the frequency of resistance genes increases in the population, demonstrating evolution by natural selection.

• No Directional Progress: The process does not make bacteria “better” in a general sense—only better suited to survive in the presence of antibiotics.

Conclusion

The statement “Evolution by natural selection is progressive, it makes individuals ‘better'” is not true. Natural selection does not have a predetermined direction or goal; it simply favors traits that are advantageous in a given environment. Antibiotic resistance provides a clear, real-world example of how natural selection operates—by acting on existing genetic variation, favoring certain phenotypes, and driving changes in populations over time, not individuals. Understanding these principles is crucial for combating antibiotic resistance and appreciating the true nature of evolutionary change.