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.
You may also ask questions and see answers to your classmates' questions in Web Crossing in the "Talk to Jim 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:
- The On-line works of Charles Darwin
- 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)
- 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.)
- Rock Layers in the Grand Canyon
- The great Unconformity
- 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 |
An Example of Radiometric Dating
Carbon 12 & Carbon 14
- Carbon exists in the atmosphere as C12 and C14. Their ratio is almost constant; however, C12 is more common.
- Remember the process of photosynthesis? If not, review that lecture.
- What do plants take in, and what is the end result?
- Plants cannot distinguish C12 from C14, so they take both in and incorporate them into their biomass.
- The C12:C14 ratio is now the same in the plant as that in the air.
- When an aminal eats a plant, the carbon compounds in their bodies reflect the same C12:C14 ratio as in the air!
- When an organism dies, it can no longer acquire carbon (either by photosynthesis or eating)
- The C14 in the dead organism's body starts decaying to Nitrogen 14.
- After 5,730 years, half of the C14 in the organism's body has decayed to N14.
- Remember: C12 is stable, so it doesn't decay.
- To age a fossil, the proportion of C12 to C14 is measured to see how much C14 has decayed.
- If the proportion is equal to half what is normally found in the air, then the fossil is 5,730 years old!
- An advantage of C14 dating is that you can date an actual fossil, or anything that was living (becuase it contained Carbon). Many of the other elements in the table above are used to date the material in which a fossil is encased.
Science and the Shroud. An interesting application of C14 dating and the reasons why scientists usually don't rely on one piece of evidence.
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. 17.3 (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.
Fig. 17.10 (text) comparasons of "arm" bones.
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.
- Individual genes from different species can be sequenced and compared.
- These genes can come from the nuclear, mitochondrial, or chloroplast genomes.
- Mitochondrial DNA is maternally inherited (and has been used to trace human origins).
- Chromosome banding patterns and protein sequences can also be compared.
- As can patterns of restriction fragments (RFLP's), separated by electrophoresis and visualized by radioactive DNA probes.
- Basically, the more similar the patterns, the closer the evolutionary relationship. These similarities were inherited from a common ancestor and the differences arose by mutation after the species diverged from the ancestral type.
- Examples:
- 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 Hemmings
- Neanderthal DNA Sequenced
- A Breed Apart DNA Tests: Humans Not Descended from Neanderthals
- Blow to Neanderthal breeding theory from The BBC
Introduction to PCR from Access Excellence
Review Ed's PCR lecture from earlier this semester
Researchers have extracted DNA from a variety of ancient organisms
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.
Why should we study evolution?
- Wisconsin district to teach more than evolution from cnn.com
- Kansas school board's evolution ruling angers science community from cnn.com,
- Evolution and Education in the State of Illinois
- Illinois State Learning Standard 12A - Students who meet the standard know and apply concepts that explain how living things function, adapt, and change.
- Stage J - Grades 11 & 12, Standard 12A, 4
- Stage I Grades 8, 9, & 10, Standard 12A, 5
- Stage H Grades 7, 8, & 9, Standard 12A, 3
- Stage G Grades 6, 7, & 8, Standard 12A, 2
- Stage C Grades 2, 3, & 4, Standard 12A, 1
- Dealing with Antievolutionism, the importance of keeping the study of evolution in school curricula.
- Eight Significant Court Decisions from National Center for Science Education
- Five Major Misconceptions about Evolution from talkorigins.org (Thanks to Miles for reviewing this web page in Web Crossing)
- Evolution has never been observed.
- Evolution violates the 2nd law of thermodynamics.
- There are no transitional fossils.
- The theory of evolution says that life originated, and evolution proceeds, by random chance.
- Evolution is only a theory; it hasn't been proved.
- In the Name of Darwin from PBS Evolution series. An early misuse of Darwin's concept of natural selection to "explain" social inequities and promote eugenics. Thanks to Eric for reviewing this article in Web Crossing.
- Science and Creationism: A View from the National Acadamy
of Scinces
See Especially The Conclusion to this booklet. - Teaching About Evolution And The Nature Of Science from The National Academy of Sciences
- Pope John Paul II, Truth Cannot Contradict Truth Address to the Pontifical Academy of Sciences October 22, 1996
Evolution as a fact and a theory
Evolution--the process by which the genetic composition of a population changes over time--is a FACT.
- This process is all that is required to produce the diversity and
similarity of all life on this planet today.
- Evolution has occurred; it still is occurring; it has been directly
observed, documented, demonstrated, and described. Supporting evidence
for it is overwhelming (and obtained from a wide range of scientific
fields).
The mechanisms by which evolution occurs (e.g., natural selection, mutation, genetic drift) are presented as SCIENTIFIC THEORIES.
- Several theories have been proposed and debated. It is far from clear how evolution proceeds in every detail.
In summary, Darwin established the FACT of evolution, and proposed a THEORY, natural selection, to explain the mechanism of evolution.
Science as a Way of Knowing the Natural World:
- A scientist believes that the natural world is a physical reality, but that we can only construct a conceptual view of that reality based upon observation and experimentation.
- Each of us has our own view of the natural world that is viewed through the lens of our previous experience and knowledge.
- Science strives to be objective, and is founded in the belief that events can be explained fully by natural causes. Conversely, explanations based in supernatural causes are not considered to be scientific. Rocks of Ages: Science and Religion in the Fullness of Life, By Steven Jay Gould
- Scientific explanations of phenomena observed in the natural world are called hypotheses (singular: hypothesis).
- Scientific hypotheses must be testable and falsifiable. If the hypothesis is incorrect it can be tested by experimentation and/or observation and proved to be false.
- Experimentation and observations can increase our confidence that a hypothesis is a correct explanation of a phenomenon, but can never absolutely prove a hypothesis to be true.
- Once a hypothesis has been supported by many experiments and/or observations it is considered by the community of scientists to be a theory. (Note that this is very different from the common use of the word, meaning an opinion or a guess.)
- The conclusions of science are subject to change. New studies, which might utilize new techniques and equipment, may produce new information that leads to the conclusion that previously accepted theories need to be modified or changed entirely.
- Great science is replaced by greater science.