Types of Selection

(Stabilizing, Directional, Disruptive)

Natural Selection

• Animals adapting to environment• Advantaged animals survive and reproduce

Stabilizing Selection

• Most Common• Average survives

Stabilizing Selection

• Examples:

Short flowers die: No sunlightMedium flowers live: Perfect conditionsTall Flowers die: Wind damage

Lightweight babies have higher mortality rate: weakerAverage weight babies survive more often: healthyHeavyweight babies have higher mortality rate: when being born

Directional Selection

• One extreme trait is favoured

Directional Selection

• Examples…

A long time ago…Small horses died: very disadvantageousMedium horses died: disadvantageousLarge horses prospered: advantageous

A long time ago…Short neck giraffes died: could not reach leaves on treeMedium neck giraffes died: could not reach leaves on treeLong neck giraffes prospered: leaves were reachable

Disruptive Selection

• Opposite extreme traits are favoured• Average trait is eliminated

Disruptive Selection• Examples…

In an environment with black and white rocks…White rabbit lives: CamouflagedGrey rabbit dies: Seen by predatorBlack rabbit lives: Camouflaged

In an environment with deep and shallow flowers…Short beak hummingbird lives: can get pollen from flowerMedium beak hummingbird dies: cannot get pollen from flowerLong beak hummingbird lives: can get pollen from flower

• Video on Types of Selection

Works Cited