Theory can"t predict change, nor the rate of change: gradualism: idea that change occurs over billions of generations. Bacteria evolve fast due to short life span but changes like reptiles to birds happen over many generations: speciation: changes in genes so vast that two descendants" groups can"t interbreed. Otherwise there would be only one evolved species. Each time one species splits into two, it doubles chances for future speciation: common ancestry: common ancestors don"t look dramatically different. Ex: ancestor of birds and dinosaurs simply split to two descendant groups: one supporting flight and other bipedal dinosaurs. Phylogenic trees grouped based on shared traits. Phylogenic tree recognized by swedish botanist, carl. Matchbook example: match boxes can be arranged many different ways by color, country, size, etc but can"t be nested to show relations between the classifications. Because every box was created from scratch, they are not preliminary to one another nor would they perfectly fit their environments.