All polygenic traits form a bell curve. (Example of Polygenic Trait: height *A person that is average height would be graphed in the middle of the curve. A person that is way shorter or way taller than the average person would be at the bottom of the curve.*) Directional Selection: takes place when organisms at one end of the curve has a lower or a higher fitness than the organisms in the middle. It's better to be at either end of the curve, than at the middle. In Stabilizing Selection it's better to be in the middle of the curve, than at either end of the curve. An organism has higher fitness at the middle of the curve. In Disruptive Selection it's better to be at any end of the curve than in the middle of curve.