Darwin’s 4 Postulates of the Theory of Evolution by Natural Selection part 1 [15.3] SPI 2 Recognize the relationship between form and function in living things. SPI 3 Recognize the relationships among environmental change, genetic variation, natural selection, and the emergence of a new species.

Darwin’s Postulates (Ideas) Individuals in a population have variations that make them unique. Some of these variations are passed on to offspring. In every generation, some individuals are better able to survive and have more children than others due to these inherited variations. Variations that increase survival and reproductive success will have a greater chance of being passed on than those that do not

Medium Ground Finch Lives on the Galapagos Islands One of the species studied by Charles Darwin Eats seeds For 551 days from late 1976 to early 1978 the islands received no rain. Plants withered and finches grew hungry. The tiny seeds the medium ground finches were accustomed to eating grew scarce. Medium ground finches with larger beaks could take advantage of alternate food sources because they could crack open larger seeds. The smaller-beaked birds couldn't do this, so they died of starvation.

1) Individuals in a population have variations that make them unique. Finch Beak size, early 1976 Bigger beaks allows bigger seeds to be eaten. The critical measure is beak depth not length, since deeper beaks exert greater force per unit effort

2) These variations are passed on to offspring. 3) In every generation, some individuals are better able to survive and have children than others due to these inherited variations. Medium ground finches with larger beaks could take advantage of alternate food sources because they could crack open larger seeds. The smaller-beaked birds couldn't do this, so they died of starvation.

They are naturally selected 4) Variations that increase survival and reproductive success will have a greater chance of being passed on than those that do not. They are naturally selected

Fitness The ability of an individual to survive and reproduce (contribute his/her/its genes to future generations.) “Survival of the Fittest” is often NOT about strength! Any attribute that helps you pass your genes on contributes to your fitness.

Adaptations Traits acquired through meiosis and/or mutation that increases an individual’s fitness When a new adaptation arises in an individual, over generations it will spread through the population, changing the make-up of the population

Mechanisms of Evolution Stabilizing selection Eliminates the extreme expressions of a trait

Directional Selection If an extreme version of a trait makes an organism more fit, it will be selected for and the population will shift.

Mechanisms of Evolution Disruptive Selection Splits a population into two, favoring both extremes.