I. Fossils provide an objective record of evolution

A. fossils are preserved or mineralized remains or imprints of organisms that lived long ago

B. the fossil record supports three major conclusions

• Earth is about 4.5 billion years old
• organisms have inhabited Earth for most of its history
• all organisms living today share ancestry with earlier, simpler life-forms

C. example of new fossil evidence: whale evolution

• several types of mammals, from about 60 million years ago, are hypothesized to be possible ancestors to modern whales
• Ambulocetus natans, from about 50 million years ago, and about 3 meters long, apparently resembled modern sea lions
• Rodhocetus kasrani, from about 40 million years ago, have reduced hind limbs, flipper-like forelimbs, and were probably almost entirely aquatic
• modern whales have vestigal hind limbs and forelimbs that are flippers

D. the fossil record is incomplete

• most organisms lived and died in places where fossils do not easily form
• environments that produce fossils are wet lowlands, slow-moving streams, lakes, shallow seas, and areas where volcanic ash settles
• most remains of organisms decay or are eaten by scavengers
• some types of organisms, such as shelled organisms, fossilize more easily than others
• radiometric dating allows paleontologists, those who study fossils, to determine the age of fossils

II. Anatomy and development suggest common ancestry

A. homologous structures are those that share a common ancestor

B. the forelimbs of vertebrates are homologous, all containing the same set of bones, but in different proportions

• humerus (upper limb)
• radius and ulna (lower limb)
• carpals and metacarpals (hand & wrist)
• phalanges (fingers/toes)

C. homologous structures during embryonic development reveal common ancestry

• all vertebrates share many stages and structures during embryonic development
• tail, limb buds, pharyngeal pouches

D. vestigial structures are reduced in size and have little or no function, but are homologous to structures in related organisms

• flightless cormorants are birds with wings so reduced they cannot fly
• modern whales' pelvis bones have no apparent function, but are homologous to the pelvis of other mammals

III. Biological molecules contain a record of evolution

A. Protein

• the amino acid sequence of proteins are determined by the nucleotide sequence of DNA
• therefore, the similarities/differences in amino acid sequences reflect the time since two species shared a common ancestor
• molecules such a hemoglobin provide a molecular clock for determining the time since 2 species shared a common ancestor

B. DNA

• as species evolve from their ancestors, mutations accumulate in their DNA nucleotide sequence
• the more recently two species diverged from a common ancestor the more similar their DNA nucleotide sequences
• the more distantly two species diverged from a common ancestor the more different their DNA nucleotide sequences
• molecular phylogenetic trees illustrate the relationship between related species