Theory of Descent with Modification 1. Microevolution species are not immutable but change through time 2. Speciation lineages split and diverge, thereby increasing the number of species 3. Macroevolution over long periods of time, novel forms of life can derive from earlier forms 4. Species are derived not independently but from common (shared) ancestors 5. Earth and life are more than 6000 years old Evidence of microevolution: change through time Evidence from selective breeding (artificial selection) Observations on living organisms provide direct evidence of microevolution by showing that populations and species change over time Evidence from direct observation of natural populations Evidence from living anatomy: vestigial structures Vestigial structures useless or rudimentary version of a body part that has an important function in other, closely allied, species Both anatomy and genome of living organisms show evidence of descent with modification in the form of reduced or useless parts Evidence of speciation: New Lineages from Old Species: populations or groups of populations, within and among which individuals actually or potentially interbreed and outside of which they do not interbreed Aka biological species concept Speciation is typically not a sudden event, but a gradual process Observations on living organisms provide direct evidence of speciation by showing that populations can diverge to the point that their individuals can no longer interbreed Speciation ends with distinct populations whose reproductive isolation is irreversible Evidence of Macroevolution: New forms from old Fossil: any trace of an organism that lived in the past Fossil record: worldwide collection of fossils Extinction and Succession Law of successiongeneral pattern of correspondence between fossil and living forms from the same locale Transitional forms Transitional forms transitional species showing a mix of features, including traits typical of ancestral populations and novel traits seen later in descendants Transitional fossils document the past existence of species displaying mixtures of traits typical of distinct groups of organisms Sometimes transitional forms are predicted before they are found, allowing biologists to test hypotheses about macroevolution Evidence of Common Ancestry all life-forms are related Homology same organ in different animals under every variety of form and function (used for different functions, but have same sequence and arrangement of bones) Molecular homology shared flaws in organisms suggest common ancestry Predictive test of common ancestry using molecular homologies Exons: small coding bits Introns: separated by noncoding intervening sequences Retrotransposons retrovirus-like genetic elements that jump from place to place in the genome via transcription to RNA, reverse transcription to DNA and insertion at a new site Processed pseudogenes nonfunctional gene copies made from processed mRNA thats reverse transcribed to DNA and inserted at new location (lack introns and promoters) Since they have no function, accumulate mutations and can estimate age of pseudogene from mutation Theory of descent with modification from common ancestors makes a testable prediction about distribution of evolutionary novelties among species They should form nested sets That they do is evidence of common ancestry Age of Earth Uniformitarianism (James Hutton in 1700s) Claim that geological processes taking place now worked similarly in the past and that earth is billions of years old Against catastrophism that todays geological formation resulted from catastrophic events in the past on a scale not observed now Several independent lines of evidence indicate Earth is billion of years old- old enough to have descent with modification from common ancestor