Evidence of Evolution Write the underlined information into your notes.
Evidence #1: Comparing Anatomy • Question: What do homologous structures suggest about the process of evolutionary change?
Comparing Anatomy • Answer: Evolutionary theory explains the existence of homologous structures adapted to different purposes as the result of descent with modification from a common ancestor.
Comparing Anatomy • Homologous structures: similar structures that are shared by related species and that have been inherited from a common ancestor. • Limbs of frogs, alligator, chicken and horse have similar bones structure but different functions.
Comparing Anatomy • Similarities and differences among homologous structures help determine how recently species shared a common ancestor. • For example, many bones of reptiles and birds are more similar to one another in structure and development than they are to similar bones of mammals. • So birds are more closely related to crocodiles (reptile) than they are to bats (mammal)!
Comparing Anatomy • Analogous structures: body parts of organisms that share common functions, but not common structure and development. • Wing of a bee vs. wing of a bird.
Comparing Anatomy • Vestigial structures: inherited from ancestors but have lost much of their original size and function due to different selection pressures acting on the descendant. • Hipbones in dolphins
Think about it… • Why do organisms retain structures that are just vestiges, or traces, of the original? One possibility is that the presence of the structure does not affect an organism’s fitness, and therefore, natural selection does not act to eliminate it. Natural Selection
Lets Build a cladogram • Take a look at the pictures of the 7 cats. • How would you group them on a cladogram based on appearances? • Gallery Walk and see how other’s grouped the cats. • There is no right or wrong answer here; as long as you base your choices on specific anatomy of the cats.
Evidence #2: Biogeography • Question: How does the geographic distribution of species today relate to their evolutionary history?
Biogeography • Answer: Patterns in the distribution of living and fossil species, combined with information from geology, tell us how modern organisms evolved from their ancestors.
Closely related but different • To Darwin, the biogeography of Galapagos species suggested that populations of several bird species on the islands had evolved from mainland species. Over time, natural selection on different islands selected among individuals with different inherited variations. That caused populations on different idlands to evolve into different, but closely related species.
Distantly related but similar • In contrast, Darwin noted that similar ground-dwelling grassland birds in Europe, Australia, and Africa were not closely related, but looked similar. Differences in basic body structures among those birds provide evidence that they evolved from different ancestors. But natural selection in similar habitats caused distantly related species to develop similar adaptations—such as long legs and feet with toes adapted to running.
Biogeography • Closely related species evolve diverse adaptations in slightly different environments. • Very distantly related species develop similar adaptations in similar environments.
Lets explore… • Examine the present day locations of 7 big cats. • Read “A lesson in paleogeography” • Revise your ‘rough draft’ cladogram using the information provided. • Gallery walk and examine all the possible cladograms students created using the same information.
Think about it… • How is the gallery walk you did in class like peer review for evolutionary biologists? • Why is this an important step for the biologist?
Evidence #3: Fossils • Question: How do fossils help to document the descent of modern species from ancient ancestors?
Fossils • Answer: Many recently discovered fossils form series that trace the evolution of modern species from extinct ancestors.
Fossils • Evolution takes a long time. If life has evolved, then Earth must be very old. Geologists use radioactivity to establish the age of rocks and fossils. Radioactive dating indicates that Earth is approximately 4.5 Bya (Billion years old)!
Fossils • Paleontologists have discovered 100’s of kinds of fossils that document intermediate stages in the evolution of many different groups of modern species.
Fossils of Dorudon: an extinct intermediate between terrestrial and aquatic mammals. • Notice the bones near the tail that appear to be ‘floating’. These are the evolutionary leftover leg bones from the terrestrial ancestor of this aquatic Dorudon organism.
Lets take a closer look… Examine the organisms on your table. • The black part of the pictures represent bones and/or fossils. • The grey part of the pictures represent the size of the organism. • The skeletons are all made to be the same size for your comparison; but these organisms ranged from the size of a mouse to the size of modern day whale as you can see from the grey outlines.
Ready, set, go! • Arrange the organisms from ancient to most recent. • Use the bones/fossils to help you determine the order of the pictures. • Gallery walk and observe how other groups created their timeline or “cladograms”. • Now, check your cladogram against a similar one in your book on pages 466-7.
Think about it… • Suppose that you worked with several science teams around the world. You all shared fossils, pictures and data to come up with this cladogram as a group. It is the current accepted theory of how terrestrial mammals evolved into aquatic mammals. • Can this theory change? • If no, why not? • If yes, what has to happen?
Evidence #4: Comparing Development • Question: What do similarities in development suggest about the process of evolutionary change?
Comparing Development • Answer: Similar patterns of embryological development provide further evidence that organisms have descended from a common ancestor.
Comparing Development • Researchers noticed a long time ago that the early developmental stages of many animals with backbones look very similar. • Recent observations show groups of embryonic cells develop in the same order and in similar patterns to produce many homologous tissues and organs.
Comparing Development Activity • Can you distinguish between the turtle, human, fish and salamandar at the first stage of development? • What about at the second stage? • What about at the third?
Comparing Development • Because these organisms share a common ancestor, they all have similar developmental genes or DNA. • They all begin developing in much the same way. • Eventually though, their DNA will begin producing traits unique to that species.
Evidence #5: Genetics • Question: How can molecular biology (Biomolecule = nucleic acids) be used to trace the process of evolution?
Genetics • Answer: At the molecular level, overwhelming similarities in the genetic code of all organisms, along with clearly homologous molecules, provide evidence of common descent.
Genetics • All living cells use information coded in DNA and RNA to carry information from one generation to the next. • This genetic code is nearly identical in almost all organisms, including bacteria, fungi, plants and animals. • This is powerful evidence that all organisms evolved form common ancestors that shared this code.
Genetics Activity #1 • Grab a text book, a scrap piece of paper and a calculator! • Turn to page 470. • In the “Analyzing Data” section, do #1-4 and write your answers on your paper. • Show your work for #1 and 2! • Write in complete sentences for #3 and 4.
Genetics Activity #2 • http://www.hhmi.org/biointeractive/creating-phylogenetic-trees-dna-sequences
Genetics Activity #3 • Obtain homologous pieces of DNA of the 7 big cats. • How do they compare? • Which cats seem to be closely related? (very few differences) • Which cats seem to be distantly related? (Many differences) • Which cats are intermediates? • Revise your cat cladogram now that you have new evidence. • Gallery walk and see how other groups made their cladograms.