TYPES OF NATURAL SELECTION

 Directional Selection  Stabilizing Selection  Disruptive Selection DEFINE IN YOUR NOTES

 A form of natural selection; occurs when individuals at one end of the distribution curve have higher fitness than individuals in the middle or at the other end of the curve.  One EXTREME is favored. DIRECTIONAL SELECTION

 Example: Giraffes  Selection for a long neck DIRECTIONAL SELECTION

 A form of natural selection; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end.  EXTREMES are NOT selected AVERAGE is better. STABILIZING SELECTION

 Example: Human infant birth weight—it is a disadvantage to be really small or really big, and it is best to be somewhere in between. STABILIZING SELECTION

 A form of natural selection; occurs when two individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle.  BOTH EXTREMES are selected for. DISRUPTIVE SELECTION

 DARWINS FINCHES DISRUPTIVE SELECTION

WORD ASSOCIATIONS  Directional = 1 extreme  Stabilizing = Average  Disruptive = 2 extremes

 Structure's that evolve because of the same environmental pressures.  For example, Birds and Bats. They do not have a recent common ancestor, but have managed to both evolve wings. ANALOGOUS STRUCTURES

THE FOUNDER EFFECT  The loss of genetic variation when a new colony is formed by a very small number of individuals. (This is why incest is not good) Wallace.html

ISOLATING MECHANISMS  When a new species evolves it’s because a population has become reproductively separated.

REPRODUCTIVE ISOLATION THERE’S 3 TYPES  When members of 2 populations cannot interbreed and make fertile offspring. This is why we will never have a real life CatDog. Different species CANNOT combine and reproduce.

BEHAVIORAL ISOLATION  This is when the same species are CAPABLE of reproducing but DON’T because they have different mating rituals. Like a lion and a cheetah. BOTH are felines (cats) BUT they DON’T mate with each other.

GEOGRAPHIC ISOLATION  When species are separated by a geographic barrier, like an ocean, river or mountains. Like a Brown Bear and a Polar Bear They are BOTH bears BUT they are geographically separated so they can’t mate.

TEMPORAL ISOLATION  When species reproduce at different times. For example, these 2 different types of frogs BOTH are frogs BUT one mates in the spring, while the other mates in the fall

ISOLATING MECHANISMS  Each of these could lead to the development of a new species.