Biology 100/101
Lecture 26
Macroevolution: Evidence
(Print Version)
Announcements
| Text Readings in Lewis et al. |
Testing Your Knowledge | Thinking Scientifically |
|---|---|---|
| Ch. 17, Evidence of Evolution | Pg. 343, Questions 1,2,4 | Pg. 343, Questions 1-6 |
Much of the material cited in this lecture outline came from your textbook (Lewis et al., 2004, Life Fifth Edition). It is highly beneficial to read this chapter carefully before your final exam.
Answers to many of these questions can be found at the Text On-Line Learning Center
You may also ask questions and see answers to your classmates' questions in Web Crossing in the "Talk to Steve and Ed" discussion.
Objectives:
After studying this material you should be able to:
- Explain what a fossil is and how it is formed.
- Explain the methods used to determine the age of a rock or fossil.
- Describe what is meant by transitional fossils.
- Describe how comparative anatomy and embryology provide clues to evolutionary relationships among species.
- Explain the difference between homologous and analogous structures and why this difference is important in ascertaining evolutionary relatedness.
- Describe how vestigial organs provide clues to the organism's origin.
- Describe how the comparative analysis of DNA sequences can be used to trace evolutionary relationships.
- Describe what a molecular phylogeny is and be able to interpret what it means.
- Know these terms and the relationships among them:
| fossils | relative dating | radiometric dating |
| half-life | comparative anatomy | vestigial organs |
| comparative embryology | molecular evolution | comparative DNA sequencing |
| phylogeny | amber | PCR |
| molecular phylogeny | transitional fossils | Archaeopteryx |
| homologous structure | analogous structure | mitochondrial DNA
|
Web Resources:
- PBS Evolution Series
- PBS Evolution Library
- Evolution Web Sites from the University of Virginia.
- Evolutionary Biology from the Talk.Origins archive.
- Talk.Origins Archive "Must-Read Files "
- Evidence for Evolution: An Eclectic Survey from the Talk/Origins Archive.
- Teaching About Evolution And The Nature Of Science from The National Academy of Sciences
- Dealing with Antievolutionism, the importance of keeping the study of evolution in school curricula.
- Mice, men share 99 percent of genes from CNN.com
- Evolution is a Fact -- If you haven't read this paper yet, do so.
- TheTree of Life Home Page
What is a Fossil and How is it Formed?
- Trilobite fossil (400 mya)
- Archaeopteryx fossil (140 mya)
- National Geographic Dinorama
- Australopithecus afarensis (Lucy) (3.6 mya)
- Downie and hominid fossils, from Sterkfontein Caves, Cradle of Humankind, South Africa ("home of our ancestors'), fossils up to 3.3 mya uncovered here.
- Homo erectus (1.6 million-35,000 years ago)
- Embryonic dinosaur teeth and skin, Fig. 17.4 (text), 89 mya
- Oldest male fossil discovered, 425 mya!, Science, Dec. 5, 2003 issue
- A fossil is evidence of past life.
- An organism, or its presence (tracks, trails, footprints, burrows), is preserved in rock (as a fossil).
- Impressions and mineralization (the replacement of parts of organisms by minerals)
- Most fossils are the hard parts of organisms (bones, teeth, shells); soft parts are rarely preserved.
- To be adequately preserved, an organism must be in an environment where it is protected from oxidation and bacterial decay. An aquatic environment, particularly one with a high sedimentation rate (swamps, tar pits), is best to preserve fossils.
- Fossils, starting as from far back as 3 bya, indicate that life evolved through great stretches of time and diversified.
Determining the Age of Rocks and Fossils
- Relative dating techniques
- In a "normal" horizontal sequence of rocks (e.g., marine sedimentary), the oldest rock types will be on the bottom with successively younger rocks on top. Sediments are deposited gradually in a flat layer and are spread over a large area. (May not be useful in the rock has been folded.)
- Stratigraphic Illustration from Berkeley
- Geologic Time Scale. Developed in the 1800's from the relative dating of rocks and the fossils each layer contained. Major boundaries indicate mass extinctions. (Note changing landmasses. As gene pools diverged, allopatric speciation occurred.)
- Index fossils - an assemblage of fossils that characterize a particular rock unit. Organisms have evolved and gone extinct through time. Fossil content can be used to help determine age of rock, and to correlate rocks from different localities.
- Radiometric (absolute) dating techniques
- This method uses naturally-occurring radioactive isotopes. Radioisotopes decay at a constant rate to form stable (or daughter) isotopes. This rate of decay is measured by half-life (how long it takes for one-half of the parent radioactive material to decay to a daughter product). The ratio of parent isotope to daughter isotope in the rock reveals the number of half-lives, or length of time in years, that has elapsed. Think of radioactive elements as "geologic clocks."
- Potassium 40 and Carbon 14 are often used to assign dates to fossils.
- Not all rocks can be dated absolutely, so a combination of techniques is used.
Half Lives for Radioactive Elements
| Radioactive Parent | Stable Daughter | Half life |
|---|---|---|
| Potassium 40 | Argon 40 | 1.25 billion yrs |
| Rubidium 87 | Strontium 87 | 48.8 billion yrs |
| Thorium 232 | Lead 208 | 14 billion years |
| Uranium 235 | Lead 207 | 704 million years |
| Uranium 238 | Lead 206 | 4.47 billion years |
| Carbon 14 | Nitrogen 14 | 5730 years |
Transitional Fossils
- Is one that looks intermediate between two species or higher lineages. Ideally, the transitional fossil should be found stratigraphically between ancestor and descendant lineages.
- Thousands of such fossils exist.
- Theropod dinosaur Protoarchaeopteryx, 145 mya. A feathery dinosaur, linking dinosaurs to birds.
- Archaeopteryx, a mixture of bird and reptile features.
- All about Archaeopteryx
- Are birds really dinosaurs? Birds are not only descended from dinosaurs, but, as some biologists insist, are dinosaurs. They are also reptiles. See Fig. 17.2 (text), an evolutionary tree, for more information.
- Transitions from early ape to human, from PBS Evolution
- Transitional Vertebrate Fossils from the Talk.Origins Archive
- Trilobites
- Brachiopods
Other examples:
Comparative Anatomy and Embryology
How do you explain the many anatomical and embryological similarities seen among different modern species? The features originated in a common ancestor, then gradually became modified as its descendants adapted to their environments.
- Skeletal organization reflects common ancestry, Fig. 17.9 (text). All vertebrate skeletons consist of basically the same parts.
- Comparative Vertebrate Anatomy, Fig. 17.10 (text), revealing adaptions that underlie the evolution of flight.
- Embryo Resemblances, Fig. 17.13 (text). The embryos of many vertebrates look alike, particularly early in development, and support the concept of common ancestry.
Homologous structures: Similar structures in different organisms having a common evolutionary origin. Example: The similarity of embryos and skeletons of vertebrates suggests common ancestry. The structures may or may not have similar functions, but they share a common origin.
Analogous structures: Structures that are similar in function among different species but that evolved independently, perhaps in response to similar environmental challenges. They are NOT inherited from a recent common ancestor.
For additional information:
Vestigial Structures
- A structure that seems not to have a function in an organism but resembles a functional structure in another type of organism. For example, whales have useless pelvic bones and, occasionally, rear feet resembling those in other mammals. Some snakes have leg bones.
- Humans have an appendix, gooseflesh, ear muscles, and as embryos, tails and gill slits. To possess these structures, we must have the genes for making them.
- Evolution is not a perfect process. As environmental changes select against certain structures, others are retained, sometimes persisting even if they are not used (Lewis et al., page 334).
- Vestigial Femurs in snakes, Fig. 17.12b (text)
- When whales had legs, from Scientific American
- Further examples, by Science Explained, UK.
Molecular Evolution
"We are the products of the genes of our ancestors." All life forms based on DNA and 20 amino acids.
Introduction to PCR from Access Excellence
Researchers have extracted DNA from a variety of ancient organisms
- Amino acid sequencing of cytochrome c, Fig. 17.16 (text)
- A phylogeny of humans and relatives, Fig. 17.15 (text)
- A "modern" application - Thomas Jefferson and Sally Hemings
- Neanderthal DNA Sequenced
Phylogeny of 8 Species Based on DNA Sequencing
Interpretation:
- All species are evolutionarily related and share a common ancestor.
- Species are related based on the presence of shared and uniquely-derived point mutations.
- Relationships can be inferred (e.g., Species E is more closely related to Species F than to any other species; Species group E and F is more closely related to species group G and H than it is to any other species group).
In actuality, thousands of DNA nucleotides can be compared and computers are used to analyze the data and construct the phylogeny. The DNA used can be from any organism, living or dead (and from fossils too).
A phylogeny is a diagram that depicts the lineages, or evolutionary relationships, among species. Comparative anatomical, embryological, molecular, behavioral, physiological, chemical, geographical, and fossil data can all be used, together or separately, to construct a phylogeny.