Lecture17.pdf

Page 1 More Macroevolution? Chapter 14 Review plate tectonics and radiometric dating, to remind yourself of the concepts. The fossil record provides a timeline See Table 14.1 in the text for a general idea of what happened when Extinction Flip side to speciation 99% of all species that have ever lived are now extinct (consider continuous turnover; production plus extinction) Background extinction Low level that happens all the time (estimated at 1(-10) species/million per year, or 10-100 species per year) Species usually persist for 1 million (mammals) to 10 million years Six major mass extinction events Mass extinctions (but not instantaneous) 250 Mya - 90% of species Cause unknown 65 Mya - dinosaurs and 75% of all species Asteroid impact Present (extraordinarily rapid rate) Destruction of habitat - rain forests Mass extinctions 10 km-diameter asteroid hit in Yucatan area; iridium deposits; end of dinosaurs and many other species K-T extinctions (Cretaceous-Tertiary boundary, 65 MYA) Page 2 Current extinction rates: ~27,000 species per year in the tropics alone 89 species of mammals in the last 400 years; = 45X the normal rate of 1 per 200 years plus 169 species critically endangered 5-20 million years to recover what we will likely lose in a century Adaptive radiation of mammals after the K-T impact 65 MYA removed the last of the dinosaurs one of the earliest placental mammals 125 MYA Phylogeny: evolutionary history of an organism homology (shared ancestry) vs analogy (same function, different ancestry) Systematics: the naming of species (taxonomy) and study of evolutionary relationships among them taxon = taxonomic (naming) unit at any level (plural: taxa) Phylogenetic trees depict hypotheses about relationships Cladistics: identification of (monophyletic) branches (clades) of related organisms Cladograms depict shared characters shared primitive characters (in an ancestral group) shared derived characters (shared among the present group) Page 3 Birds and crocodiles are more closely related than crocodiles and lizards/snakes DNA sequences show relationships The more recently two groups diverged, the more similar their DNA sequences DNA coding for ribosomal RNA changes slowly--is useful for showing ancient relationships The DNA in mitochondria evolves rapidly, so it can be used to investigate recent evolutionary changes e.g., human populations in North America over the last 15,000 years Genome evolution Since molecular sequences of entire genomes (or almost entire) have become available for more organisms, one can establish relationships humans and chimpanzees--genomes are 99% the same homologous genes--widespread humans and yeast (50% of our genes are homologous) The three-domain system of classification of organisms Evolution?probably the best-documented fact in biology. Darwin?s proposal that natural selection is the main mechanism for evolution is a well-supported theory. Distinguish theory as used in science from its use in common language. (last para. Origin of Species) Tom Jurik L17 Evolution 3 S10.ppt