Evolution: Natural Selection

Natural Selection: The Mechanism for Evolution Definition: Process by which organisms that are best suited to their environment survive and reproduce most effectively A mechanism that works in nature as artificial selection works with the aid of humans What is artificial selection? How are they similar? Different?

Natural Selection: How Does it Work? 1. Organisms produce more offspring than their environment can support Struggle for existence Many individuals die due to: disease, starvation, predation, etc. Only some individuals survive to reproduce Examples??

Natural Selection: How Does it Work? 2. There is variation within populations Many variations are inherited Some variations are favorable Adaptation: a heritable characteristic that increases the ability of an organism to survive and reproduce Examples?? Camouflage Antibiotic or pesticide resistance Mimicry Behavioral

Natural Selection: How Does it Work? 3. Fitness: those individuals with favorable variations survive and reproduce These variations are inherited (and passed on to offspring) Therefore, offspring will also have these variations ??What could happen if the environmental conditions that favor these traits were to change?? 4. Over long periods of time, genetic changes can accumulate Evolution: The change in genetic frequencies in a population over time Punctuated Equilibrium theory (Steven Jay Gould) Doesn’t always take as long as Darwin originally thought (examples??)

EXAMPLES OF ADAPTATIONS

Types of Natural Selection 1. Directional Selection: Population moves to one extreme 2. Stabilizing Selection: Population moves to the middle 3. Disruptive Selection: Moves away from middle to both extremes