1. Summary

Natural selection is not the evolution of a species. It is the process of genes or characteristics being naturally selected, which are essential for the survival of a species. The gene or characteristic doesn’t always go away—it can still be there—but the gene that is better for survival will be more dominant.

2. Why Watch This Video?

• Do you wonder why some species have a change of characteristics over time?
• Do you want to know an example of how evolution might occur?
• Do you wonder if natural selection is important?

3. Key Terms

• Natural selection – the selection of a trait within a species that would result in a higher survival rate, by virtue of individuals with that trait surviving and reproducing.
• Evolution – the change of a species over time, either a small change or an entirely different change.
• Mechanism – the processes used in order for an event to occur (such as natural selection).

4. Loose Ends

Natural selection is not evolution itself.

Natural selection is a mechanism of evolution, which means it is a process that can lead to the occurrence of evolution but is not a sole means of a species evolving.

Fitness isn’t what you think it is.

Fitness is not the physical capability of a species to survive (e.g., physical strength), it is more of how characteristically capable they are of surviving.

What do antibiotics and bacteria have to do with any of this?

In the video, antibiotic resistance (the fact that some antibiotics don’t work anymore) is discussed. The problem of bacteria becoming resistant to antibiotics is an example of how natural selection works. When you don’t finish a course of antibiotics as prescribed, you kill some of the bacteria, but the ones more able to resist the antibiotic remain. This means you are selecting for bacteria that are better at not being treated by antibiotics. Done often enough, this can weed out all bacteria except the ones for which the antibiotic has no effect.

5. Self-Test Questions