Feb 28: Phylogeny: Whence and Why The &quot;Ultimate&quot; Questions: History and Function Can we study history without function? History by itself provides no explanation of CAUSES of evolutionary change Note: Natural Selection is not the only agent of evolutionary change Genetic drift Recombination Hybridization Can we study function without history? Studies of function are about how natural selection has &quot;designed&quot; trait for particular challenges to survival Knowing the historical origins of traits makes clearer the starting point and subsequent path of the design process May reveal why some outcomes were achieved rather than others May reveal the constraints on the evolutionary process: how easily traits can arise and be lost May help test ideas about function: the evolutionary pressures favoring the evolution of particular designs Feb 28: Phylogeny--Comparative Method I How to Infer History of a Trait Without Fossils Comparative Method I Study other living species that exhibit traits similar to the trait in question Comparisons among species can suggest evolutionary progression in trait Problem: this approach assumes that similarities among the comparison species are a result of their being part of same evolutionary series, which may not always be true Feb 28: Phylogeny--Homology and Homoplasy Homologous and Homoplastic Similarity Homology: similarity resulting from descent from common ancestor (within same evolutionary lineage) Homoplasy: similarity resulting from convergence in independent evolutionary lineages Examples: Opposable thumbs in primates and pandas Camera eyes of vertebrates and cephalopod molluscs Evidence for homology Embryology Genetics Common neuronal substrate Close phylogenetic relationship? (avoid circularity) http://www.accessexcellence.org/AE/AEC/CC/vision_background.html http://biodidac.bio.uottawa.ca/Thumbnails/CEPH005B-GIF.htm Feb 28: Phylogeny--Cladistics Comparative Method II: Cladistics The cladistic method explicitly recognizes difference between homologous and homoplastic similarity Makes assumption that homoplastic similarity is harder to achieve than homologous similarity (because it requires independent evolutionary events, and evolution is a conservative process) By parsimony, the likeliest evolutionary scenario is the one that involved the fewest evolutionary changes Homoplasy is inferred if it is most parsimonious intepretation Similar trait (yellow bill) in two bird species Black Black Yellow Yellow Black Yellow Black - Black - Yellow Homoplasy Homology (more parsimonious) + Homology Homoplasy (more parsimonious) Feb 28: Phylogeny--Cladistics cont d Cladistics cont d Two goals in cladistics Construct tree representing <a href="/keyword/phylogenetic-relationships/" >phylogenetic relationships</a> The most likely tree is one that requires fewest evolutionary changes Use tree to study evolutionary history of other traits The most likely history is one that requires fewest evolutionary changes GW Beyersbergen http://raysweb.net/specialplaces/ pages/pelican.html Feb 28: Phylogeny--Cladistics cont d Cladistics cont d Behavioral cladogram of pelicans and their relatives Pelicans Gannets Boobies Anhingas Alcock Fig. 7.4 Feb 28: Phylo...