Biology 3201 Unit 4 Evolution Ch. 19 Introducing Evolution Part 2 Evidence supporting the modern theory of evolution The following are pieces of evidence that supports the modern theory of evolution: 1. Fossil record 2. Biogeography 3. Comparative anatomy A. Homologous structures B. Analogous structures C. Vestigial structures 4. Comparative embryology 5. Heredity 6. Molecular Biology 1
Fossil Record Fossil: remains or traces of once living organisms. Often preserved in rock Fossil evidence supports evolution in the following ways: A. Fossils from more recent geological eras are more similar to present day organisms than older fossils (supports the idea that life has evolved over time) B. Fossils appear in chronological order in sedimentary rock. Younger fossils appear higher in sedimentary layers and are more complex than older fossils appearing in deeper layers (supports the idea that as evolution has occurred, species of organisms have become more complex) C. Transitional fossils: make links between different sets of related organisms within differing fossil layers Ex. Archaeopteryx shows a relationship between reptiles and birds (this suggests that evolution is occurring over time from less complex to more complex life forms Finding the age of fossils/dating fossils There are two methods to determine the age of a fossil 1. Relative dating: judging the age of a fossil according to its position in the rock layer. Ex. Fossil B is younger than fossil C but older than fossil A. A B C 2
Finding the age of fossils/dating fossils 2. Absolute dating: finding the exact age of a fossil using radioactive dating Radioactive dating: a method of finding the age of a fossil using the half-life of certain radioactive substances that decay over time. The radioactive substance decays into a more stable daughter element Half-life: period of time required for 1/2 of a radioactive isotope to decay into a more stable element. Isotopes Representative radioactive isotopes with half-life Radioactive parent Stable daughter Half-life (years) C14 N14 5730 U235 Pb207 713 000 000 K40 Ar40 1 250 000 000 Rb87 Sr87 48 800 000 000 3
Half-life Calculations involving half-life A. Finding amount of sampling remaining Ex. A 10 kg of C14 has underwent 4 half-lives. How much of the original sample remains? Ans: (1/2)(1/2)(1/2)(1/2) = 1/16 Now multiply 1/16 by the original mass 1/16 x 10 kg = 0.625 kg remaining. 4
Calculations involving half-life Finding the half-life (turn required for a substance to decay to 1/2 it's original amount) Ex. A rock is found to be 33, 000, 000 years old and it contains 1/64 of the original sample. What is the half-life of the rock? First, find the number of half-lives. Think (1/2) to what power would give 1/64. It would be 6. Therefore there would be 6 halflives. Next, divide the age of the rock by the number of half-lives to find the value of one laf-life 33000000 / 6 = 5, 500, 000 years/half-life Calculations involving half-life C. Finding the age of a fossil Ex. A fossil contains 1/32 of the original U-235. What is the age of the fossil if the half-life of U-235 is 713, 000, 000 years? First, calculate the number of half-lives. Think 1/2 to what power is 1/32. The answer is 5. Next, we use 5 half-lives and multiply by the value of a single half-life to get the fossil age 5 x 713, 000, 000 = 3, 565, 000, 000 years old 5
biogeography Biogeography: the study of the geographical distribution of species Darwin noted that the birds of the Galapagos islands were similar to those on the mainland of South America Geographically close environments (deserts and jungles of South America) are more likely to be populated by related species rather than locations that are geographically separate but environmentally similar (desert of Australia and a desert in Africa) comparative anatomy This is a comparison of physical structures in differing organisms that may suggest a common ancestor. Homologous structures: these are body structures in different species which have the same origin but differ in structure and function (ex. Human arm, frog leg, bat wing). These structures all have a similar number of bones/ligaments suggesting they came from a common ancestor, but they all have a different structure and function. 6
comparative anatomy Analogous structures: these are structures that have different origins but similar function (ex. Bird and insect wings) Vestigial structures: these are structures that were functional in ancestors, but have no current function (pelvic bone in baleen whales, wings in ostriches) comparative embryology This is a comparison of embryos from various species to indicate relationships among organisms. Many organisms have similar stages of development. For example, all vertebrates go through a stage having a gill pouch. 7
comparative embryology heredity Knowledge of heredity can explain how variations can occur in a population allowing members of that population to be better suited to their environment and thus undergo natural selection. 8
molecular biology This is a comparison of the DNA and proteins within various species to indicate relationships/similarity The closer the DNA sequences are between organisms, the more closely related the species are. This may suggest a common ancestor. Ex. Humans and chimpanzee DNA differs by only 2.5 % 9