1	Radiations and Rapid Change There are times and situations in which species arise at very high rates.
2	Reading For today’s lecture read Box 26.1 on Molecular Clocks Read p. 573 – 580.
3	Neutral Substitutions Redundancy in the genetic code means that base pairs in DNA can change without changing the amino acid in the protein. Most of the base substitutions that don’t change the amino acid sequence are in the third codon position. Neutral substitutions accumulate thru time.
4	The molecular clock Base pair changes that do not change the amino acid accumulate among populations of a species that are geographically isolated. Some amino acid substitutions result in functionally equivalent alleles which drift. When accumulations of differences are calibrated using fossils, the results suggest the number of differences can be used to estimate the time of divergence.
5	Accumulation of neutral substitutions Figure 26.10 shows the accumulation of differences in hemoglobin. Because the points are close to a straight line, the % differences between to species can be converted to an estimate of the time to the most recent common ancestor. Different proteins accumulate differences both faster than hemoglobin and slower than hemoglobin.
6	Radiations If many species originate at about the same time the phylogeny will be difficult to force into a bifurcating pattern. Data analysis may give more than two species arise from a node (at same time). If more than two branches arise from a node the terms ‘star phylogeny’ or ‘polytomy’ are used.
7	Adaptive Radiations Are best known from islands Presumably, a few individuals of species arrive on the island and the population expands rapidly. Differentiation of species takes advantage of the diverse opportunities available in a habitat without many species. The Galapagos and Hawaiian islands are well studied examples. Both are very far from other islands or continents.
8	More on Islands Studies of lizards on Caribbean islands suggest that no matter which type of lizard arrives first, the island will end up with the same array of ecological types; according to height of foraging. The Hawaiian islands have produced an diversity of species types that is not replicated elsewhere to my knowledge.
9	Mass Extinction Events have occurred in the history of the earth that resulted in the extinction of a large number of species in a short period of time. Five big events of extinction have occurred in the last 500 million years. The most recent mass extinction (65x10⁶ ya) resulted in the disappearance of the dinosaurs and the rise of mammals.
10	Events and mass extinction A variety of evidence (Iridium and ‘shocked quartz’) suggests that the Cretaceous (age of the dinosaurs) was ended when an asteroid hit the earth. Only 18,000 ya our current location was covered by a glacier a mile thick. Obviously things were quite different not very long ago.
11	Mammalian radiation After the mass extinction that marked the end of the Cretaceous the diversity of mammals greatly expanded. Though Cretaceous mammals were all small and not very diverse within 15 million years of mass extinction all current orders of mammal existed. No new mammal orders in last 50 million years.
12	Rapid genetic change Instances of rapid genetic change have been discovered after it was possible to use museum skins to look at populations from the past. Pergams, Barnes & Nyberg (2003) Nature 423:397 reported that the mitochondrial haplotype of the white-footed mouse that was common in Chicago in 1900 is now very rare.
13	The anthropogenic world Human inventiveness and economic activity is altering the world. We have just about finished converting all natural areas to agricultural use throughout the world. We are transporting species deliberately and inadvertently throughout the world. Many species are in danger of extinction from human economic activity.
14	Human caused Extinction The passenger pigeon was the most abundant bird in North America at the time of the signing of the constitution. One hundred years later the Passenger pigeon existed only in zoos. It is now extinct. The behavior of the Passenger pigeon made it vulnerable to human hunting.
15	Pollution Pollution is a contamination of a place with stuff that changes the place. Pollutants traditionally ‘foul’ the environment, i.e., make it smell or look bad. The idea of pollution has been expanded to heat, a physical attribute.
16	Biological Pollution Exotic or non-native species can be described as biological pollution. Biological pollution is a greater threat than garbage because species reproduce (and can spread on their own). Biological pollution is a major cause of extinction of native species (see the essay on p1164).
17	Vocabulary Redundancy Codon Neutral substitution Polytomy ‘star phylogeny’ Adaptive radiation Mass extinction Biological pollution Cretaceous Rapid evolution