This refers to natural classification: How organisms truly grouped together in nature  Identifying unknown organisms, using ID key  How organisms related evolutionarily (DNA evidence for current species; anatomical for fossils b/c no DNA)  Predicting characteristics similar to those found in related organisms

 Supports Mendel’s, Darwin’s ideas  Universality…genetic engineering ◦ Not possible unless have a common ancestor!  All proteins in all living organisms use same 20 amino acids ◦ Can engineer organism to synthesize a new protein never made before ◦ All are left-handed…no right-handed ones! TOK: The universality of DNA and the genetic code had a profound effect on Marshall Nirenberg and other pioneering biochemists, as it showed that humans were part of the overall tree of life and were not set apart genetically. This must affect the way in which we view ourselves and the rest of the living world.

 Phylogeny: study of evolutionary past of a species  Most similar = most closely related  Molecular evidence ◦ Polypeptides  Hemoglobin, cytochrome C (mitochondrial), chlorophyll  DNA sequencing (nuclear, mitochondrial)  Compare! TOK: Variations are partly due to mutations, which are unpredictable and chance events, so there must be caution in interpreting them.

 Mutations occur each generation  Differences accumulate steadily, gradually  Estimate time 2 related species split  Count # differences in molecules (base pairs) ◦ More diff = longer since split ◦ Use mathematical model to infer time periods  Example in book—p. 451  ESTIMATE! Compare to morphological data, etc. TOK: We must be careful not to suggest that this clock moves on at a constant and invariable rate, so interpretation of data here must be very carefully done, with the uncertainties made clear.

 Cladistics: grouping taxa according to recently evolved characteristics  Primitive traits (plesiomorphic) ◦ Same structure & function, evolved early  & derived traits (apomorphic) ◦ Same structure and function, but evolved more recently as modification of previous trait  shared by organisms   more recent vs more distant splits

 Clade: ◦ Group with certain derived traits, different from the group it splits with ◦ (2 groups are 2 separate clades)  Monophyletic: ◦ Most recent ancestor & all descendants

 Analogous ◦ Same function but not necessarily same structure ◦ Not derived from common ancestor ◦ Wings: pterosaurs, birds, insects, bats ◦ Not in same clade of “flight”; must consider many other differences ◦ Fins: dolphin, shark (mammal vs fish)  Homologous ◦ From same part of Common ancestor ◦ Pentadactyl limb (human, bat, whale)—same general format ◦ Eyes (molluscs to birds)

 Cladogram: visual diagram to show evolutionary relationships  List organisms to be included  List characteristics of each ◦ Morphological, biochemical, etc.  Search for commonalities and differences, make a table (-, +) ◦ Derived traits  Place accordingly  Node (split) = new species/clade  Ancestral trait = common to all (primitive characteristic)  Fewest derived traits = bottom of cladogram ◦ “Oldest” in evolutionary terms  Most  top ◦ Most recent to evolve

Morphological or biochemical data can be used. Example –p. 455

Example from class  Ancestor  Primitive characteristic  Timeline of sorts  Close on cladogram branches = closely related vs farther apart  Lines on cladogram = derived characteristics ◦ All organisms above it share the char.

 Derived nodes can be used to interpolate the classification of a group ◦ Hair  mammals  Oddities...birds. Feathers are unique, but share MANY other char. w/dinosaurs ◦ Linnaean groups not clearly defined (phylum = ???) ◦ Clades are more clear-cut; more likely that birds evolved from dinosaurs instead of another common ancestor