3 domains of life: archaea, bacteria, eukaryotes, archaea & eukaryotes are more similar, they share a common ancestor. Cladistics: cladograms aka tree of life show relationship between organisms, built by, analyzing dna, synapomorphies - shared traits of their common ancestor, coherence - justifications via multiple fields of study, synapomorphy for all eukaryotes is membrane bound organelles. Scientific theory - proposed explanation for general phenomena that is well supported: pattern component - description of what is occurring, descent w/modification, process component - explanation for what is occurring (why, change in allele frequency (ns) Embryo stages and axes are the same: main conclusions, species change over time, descent w/modification, species are not independent creatures. If they die before their reproductive age, traits cannot be passed on. Story of the earth: earth is 4. 5 by old, no atmospheric o2 at this time and lots of solar radiation.