 Do you think these two organisms evolved from a common ancestor? ◦ What evidence would you need to convince yourself?

 Layers of rock contain fossils ◦ Newer layers of rock cover older ones ◦ Creates a timeline  Fossils can show a record of organisms that lived on Earth over a long period of time

Many fossils link early extinct species with species living today Example: Tiktaalik- “missing” link between land and sea animals.

A transitional species: Tiktaalik

 Like a fish complete with scales and gills  Flattened crocodile head with unusual fins  sturdy interior bones that would have allowed Tiktaalik to prop itself up in shallow water and use its limbs for support as most four-legged animals do.

Ancient reptile Thrinaxodon ancient mammal

Refers to structural similarities found between related organisms Homologous structures – Limbs that perform different functions but are built from the same bones HumanCatWhaleBat

 Species that are only distantly related develop similar adaptations and resemble each other ◦ Because they live in similar environment and are exposed to similar selective pressures On pre-test: 59% got this wrong

Analogous structures – structures that resemble each other due to similar selective pressures and not to recent common ancestry

 Remains of structures that were functional in ancestors ◦ Eyes on a blind cave fish

 Remains of structures that were important to the organisms’ ancestors but are not to the existing organisms  Whale Video ◦ 9:15 On pre-test: 76% got this wrong!

 Similarities in DNA and proteins  Amino acid sequences can be compared among various species for minor changes  The more similar the code, the closer related

yeast (Candida) mothfishturtleduckpigmonkeyhuman Types of Organisms Number of Amino Acid Differences Compared to Human Cytochrome c Biochemical/Molecular Data Branch points tell the number of amino acids that differ between human cytochrome c and the organisms depicted

Percent Agreement between Beta Globin of Various Species SpeciesHumanChimpGorillaRed foxDog Polar bear HorseRatChicken Human Chimp Gorilla Red fox Dog Polar bear Horse Rat Chicken

 Closely related organisms go through similar stages in embryological development  Organisms that appear different as adults may be very similar in embryonic stages = common ancestor

 What do you think?  Of these four (in your packet), which do you think is the strongest evidence for evolution?