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Evidence for Evolution Biogeography Fossil Records Comparative anatomy Comparative embryology Molecular biology Evolution is consistent with all scientific observations! Biogeography Species are most closely related to those near them Rain forests in different parts of the world have very different species Species tend to be very similar to the fossils found in there area – but with some changes Fossil Records The age of different fossils matches what we would expect I.e. we find that brain size has increased over time Fossils Con. Oldest vertebrate fossils are fish, then amphibians, reptiles, mammals and birds Many hypothesized intermediate species have been found, i.e. Artie, Lucy, fish with legs Comparative Anatomy The anatomies of related species are similar, even if they are used differently i.e. bones of humans, cats whales and bats are similar It seems unlikely a designer would make a Homologous Structures bat's wing similar to a whale's fin Vestigial Organs Leftover body parts that do not help a species i.e. whales still have pelvises and remnants of leg bones These structures serve no purpose in the modern animal Comparative Embryology Similar species develop in very similar ways Especially early in development, before lots of specialization has occurred Molecular Biology Closely related species are closely related in their genetic codes Also supports idea that all species are relatedall species share DNA and some proteins The “Theory” of Evolution The closely related nature of all life is really not debatable Natural selection is really the theory Well documented and thoroughly supported- like the “Theory” of Gravity Macroevolution and Speciation •Microevolution explains how populations can change over time •But how do new species or other taxonomic groups arise? Geographic Speciation •The formation of new species usually occurs when 2 populations are separated and evolve differently •Eventually the species have changed so much that they can no longer reproduce Reproductive Isolation •A byproduct of genetic differences •Different: •Mating behaviors •Mating times •Mating locations •Mating “structures” •Gametes •Or offspring that are infertile- no mixing of genes Reproductive Isolation Speciation •With no gene flow between the population, they become more and more different •This usually takes thousands to millions of years Exception - Polyploidy •Occasionally plants end up combing their full genomes (instead of half) leading to a doubling of the chromosome # •Instantly forms a new species •Extremely significant in plant evolution Biological Definition of Species •2 populations that cannot naturally mix genes •Due to any of the reproductive isolation methods •Not a perfect system Evolution is Always Occurring •Usually just slowly •Bacteria and viruses change over time – we must constantly come up with new antibiotics and new vaccines Changing Environments Accelerate Evolution •New habitats open up opportunities for evolution •Leads to adaptive radiations – where many groups evolve from a single ancestor •i.e. after the fall of dinosaurs- many mammal groups evolved One Major Change leads to many New Adaptive Radiations Imagine the first species that could breath in air Many new species would quickly evolve – lots of territories to take over! Then evolution would slow down once there is competition for space Extinction •Is the norm •Most species go extinct- but new ones survive •There have been at least 5 major mass extinctions Phylogeny and Taxonomy Tracing Evolutionary History Phylogenetic Trees Show how each species is related to other closely related species Shows common ancestors Use fossils and other evidence to reconstruct an organisms history Monophyletic Taxa We want to trace species to a single common ancestor for each taxa, and include every species that descended from that ancestor i.e. all mammals can be traced to a single mammalian ancestor Monophyletic Taxa •Includes a species and every single one of it’s descendents •I.e. Primates – include the primate ancestor and all of it’s descendents (including us!) NOT a Monophyletic Taxa •Plants and Animals (because fungi and other species share the same common ancestor) •Grouping all monkeys/apes together BUT not including humans •Reptiles (birds share the same common ancestor and should be included in reptiles!) How Do We Make Trees? •Comparing DNA •Comparing fossils/anatomies/structure/devel opment Molecular Biology Provides Great Evidence for Classification Similarities in DNA sequence Comparison of proteins The more DNA changes/protein differences, the less closely related the species Molecular Analysis Advantages •Most accurate Disadvantages •Individuals of the same species differ in •Large numbers of traits/proteins to analyze DNA •Allows us to •Can be confusing differentiate between closely related species that appear very similar DNA Base Pair Differences 1 2 3 4 5 1 x 10 20 30 40 2 10 x 10 20 30 3 20 10 x 10 20 4 30 20 10 x 10 5 40 30 20 10 x 1 2 3 4 5 1 x 10 20 30 40 2 10 x 10 20 30 3 20 10 x 10 20 4 30 20 10 x 10 5 40 30 20 10 x Practice (# of base pair differences in a gene) Cat Dog Wolf Skunk Otter Cat x 28 26 15 14 Dog 28 x 2 10 9 Wolf 26 2 x 9 8 Skunk 15 10 9 x 2 Otter 14 9 8 2 x Phylogenetic Tree Time Homology/Anatomy Analysis Find an adaptation that is present in one lineage, but not in another The phylogenetic tree branches when these new features evolved Cladistic Tables Different Species 1 2 3 4 5 Character A? Yes Yes Yes Yes Yes Character B? No Yes Yes Yes Yes Character C? No No Yes Yes Yes Character D? No No No Yes Yes Character E? No No No No Yes 1 2 3 4 5 Character A? Yes Yes Yes Yes Yes Character B? No Yes Yes Yes Yes Character C? No No Yes Yes Yes Character D? No No No Yes Yes Character E? No No No No Yes Practice DNA Organelles Cell Walls Amnion Hair Reptiles Y Y N Y N Plants Y Y Y N N Mammals Y Y N Y Y Bacteria Y N N N N Amphibians Y Y N N N Time Ancestral reptile Ancestral fish Ancestral animal Anatomy Analysis Advantages Disadvantages •Homologous structures show relationships •Analogous structures do not and can be confused •Allows us to determine when changes occurred (using fossils) •Not all species leave fossils •The fossils we have collected are •Best way to analyze incomplete extinct species Homology vs. Analogy Homology means two features are similar due to ancestry Wings in bats, arms in humans, fins in whales Called homologous structures Caused by divergent evolution Analogy is when two organisms have similar features but are not closely related Wings in bats and birds Caused by convergent evolution Evolved the same solution Embryology Analysis Advantages Disadvantages •Allows us to see similarities even when adults of the species look very different •Often similarities are lost later in development • i.e. We have gills early on in •I.e. reptiles and birds development look more closely related We did not evolve from chimpanzees!