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Figure Medium ground finch (Geospiza fortis) Daphne Major

Darwin’s Four Postulates Evolution is a logical outcome of four postulates… –populations have natural variation –the organism’s features are heritable –more offspring are produced than can survive –some individuals produce more offspring because of the environment Modern biologists condense Darwin’s four steps into two statements: Evolution by natural selection occurs when: 1. Heritable variation leads to 2. Differential reproductive success

Figure Weigh and measure all birds in the population before and after the drought. 1976: Before drought N  751 (all birds on island) Beak characteristics changed in response to a drought. No changes in beak characteristics occurred in response to a drought. Average 1978: After drought N  90 (survivors) Number of finches Average beak depth in the population increased Beak depth (mm) Natural selection occurred. The characteristics of the population have changed. Did natural selection on ground finches occur when the environment changed?

Figure Did natural selection on ground finches occur when the environment changed? No changes in beak characteristics occurred in response to a drought. Beak characteristics changed in response to a drought.

Figure Weigh and measure all birds in the population before and after the drought. Did natural selection on ground finches occur when the environment changed? Beak characteristics changed in response to a drought. No changes in beak characteristics occurred in response to a drought.

Figure Weigh and measure all birds in the population before and after the drought. 1976: Before drought N  751 (all birds on island) Beak characteristics changed in response to a drought. No changes in beak characteristics occurred in response to a drought. Average 1978: After drought N  90 (survivors) Number of finches Average beak depth in the population increased Beak depth (mm) Natural selection occurred. The characteristics of the population have changed. Did natural selection on ground finches occur when the environment changed? ?

Figure Weigh and measure all birds in the population before and after the drought. 1976: Before drought N  751 (all birds on island) Beak characteristics changed in response to a drought. No changes in beak characteristics occurred in response to a drought. Average 1978: After drought N  90 (survivors) Number of finches Average beak depth in the population increased Beak depth (mm) Natural selection occurred. The characteristics of the population have changed. Did natural selection on ground finches occur when the environment changed? What statistical value is a measure of population variation? clicker!

Figure : Before drought N  751 (all birds on island) Average 1978: After drought N  90 (survivors) Number of finches Average beak depth in the population increased Beak depth (mm) Natural selection occurred. The characteristics of the population have changed. is natural variation evident? did the drought select individuals of better fitness for increased reproduction?

Darwin’s Four Postulates Evolution is a logical outcome of four postulates… –populations have natural variation –the organism’s features are heritable –more offspring are produced than can survive –some individuals produce more offspring because of the environment Modern biologists condense Darwin’s four steps into two statements: Evolution by natural selection occurs when: 1. Heritable variation leads to 2. Differential reproductive success

Figure Geospiza fortis Shallow adult beak Geospiza magnirostris Deep adult beak Lower Bmp4 expression (dark area) in embryo’s beak 2 mm Higher Bmp4 expression (dark area) in embryo’s beak Bmp4 is a gene whose expression is shown by in situ hybridization:

Figure Bacteria Archaea Flowering plants Mosses Tapeworms Vertebrates Fungi The branches on the tree represent the relatedness of populations. All of the species have evolved from a common ancestor. None is “higher” than any other Last universal common ancestor (LUCA) Which dimension shows the progression of time?