The bananas we eat are "asexual clones". We've been eating the same banana over and over and over again.
The bananas have been bred to not produce seeds. This means that the bananas aren’t able to reproduce naturally. They can only spread when a human cuts from the base of another plant to make a new one. While this makes bananas easier to eat, it eliminates any chance of genetic adaptation for the plants. So while bananas’ natural predators (insects and fungi) have been evolving to be better suited to consume bananas, the bananas haven’t been evolving to adapt new defenses from their predators. This means it can be very difficult to produce a healthy banana crop without a lot of pesticides and fungicides.
Learn more about bananas, including the history of the banana and a fungus called Black Sigatoka that is threatening the modern banana crops.