Organisms such as bacteria usually reproduce asexually. This means that their cells simply copy their DNA and when the cells divide in two, each new cell receives a copy of the DNA. Yet
bacteria evolve over time. How can that happen?

Variation

Negative Mutations

Neutral Mutations

Positive Mutations

Female luna moths (actias luna) attract males by emitting chemical signals that spread through the air. a male hundreds of meters away can detect these molecules and fly toward their source. the sensory organs responsible for this behavior are the comblike antennae visible in the photograph shown here. each filament of an antenna is equipped with thousands of receptor cells that detect the sex attractant. based on what you learned in this chapter, propose a hypothesis to account for the ability of the male moth to detect a specific molecule in the presence of many other molecules in the air. what predictions does your hypothesis make? design an experiment to test one of these predictions.