Biology 100/101
Lecture 26
Macroevolution: Evidence
(Print Version)

Announcements

Objectives

Web Resources

What is a Fossil?

Determing Age of Rock

Transitional Fossils

Comparative Anatomy

Vestigial Organs

Molecular Evolution

Molecular Phylogeny

Lecture Syllabus

IB 100/101 Home Page

Text Readings in Lewis et al.

Ch. 17, Evidence of Evolution

Much of the material cited in this lecture outline came from your textbook (Lewis et al). It is highly beneficial to read these chapters carefully before your final exam.

The "Reviewing Concepts" boxes are valuable summaries of the main ideas in these sections of the text.

You have open access (no log-in or password needed) to instructional materials on the Text web site. Select the text chapter you want and use the links to the e-learning modules or other available materials. There is also a collection of study materials called the "Essential Study Partner" that you may find useful.

Web Crossing

You may also ask questions and see answers to your classmates' questions in Web Crossing in the "Talk to Sarah and Ed" discussion.

Objectives:

The content of today's lecture will help you complete these assignments:

Take-Home Assignment #8 - Biodiversity and Evolution due at lecture Wednesday Dec. 5.

Web Crossing Assignment #4 due at 8:00 AM Wednesday Dec. 5.

After studying this material you should be able to:

1. Explain what a fossil is and how it is formed.

2. Explain the methods used to determine the age of a rock or fossil.

3. Describe what is meant by transitional fossils.

4. Describe how comparative anatomy and embryology provide clues to evolutionary relationships among species.

5. Explain the difference between homologous and analogous structures and why this difference is important in ascertaining evolutionary relatedness.

6. Describe how vestigial organs provide clues to the organism's origin.

7. Describe how the comparative analysis of DNA sequences can be used to trace evolutionary relationships.

8. Describe what a molecular phylogeny is and be able to interpret what it means.

9. 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:

These links would provide good sources for Extra Credit Projects (due 8:00 AM Monday, December 5) or the Fourth Web Crossing Assignment (due 8:00 AM, Wednesday, December 5).

• The On-line works of Charles Darwin

• PBS Evolution Series

• PBS Evolution Library

• PBS Program Becoming Human

• 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?

• Dinosaur "mummy" found in North Dakota

  It's real life CSI for dinosaur detectives from cnn.com

• Trilobite fossil (400 mya)

• Archaeopteryx fossil (140 mya)

• Dinosaur eggs found in China from National Geographic

• Bigger than T. rex??? from National Geographic

• Australopithecus afarensis (Lucy) (3.6 mya)

• Homo erectus (1.6 million-35,000 years ago)

• Embryonic dinosaur teeth and skin, text fig. 18.4, pg. 327, 89 mya

• 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

Grand Canyon Fossils and geology

• 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."

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

• 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.

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.

Dating the Lost Gospel of Judas. from National Geographic

Turin shroud 'older than thought' from The BBC

How to age a rock. More details on radiometric dating.

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.

• New Fossils Fill the Evolutionary Gap Between Fish and Land Animals

• 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 Text fig. 18.3, pg. 326, an evolutionary tree, for more information.

Other examples:

• Transitions from early ape to human, from PBS Evolution

• Transitional Vertebrate Fossils from the Talk.Origins Archive

• Trilobites

• Brachiopods

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, Text fig. 18.9, pg. 332. All vertebrate skeletons consist of basically the same parts.

• Comparative Vertebrate Anatomy, Text fig. 18.10, pg. 333, revealing adaptions that underlie the evolution of flight.

• Embryo Resemblances, Text fig. 18.13, pg. 336. 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.

Text fig. 18.9, pg. 332 comparasons of "arm" bones.

Comparative Embryology

Hominid pelvises, femurs, and feet

The "Diver Illustration"

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.

• Homologous vs. Analogous Structures, Text fig. 18.11, pg. 334

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, text fig. 18.12b, pg. 335

• 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.

• Molecules reveal relatedness. Molecular evidence for evolution includes similarities at the gene, protein, chromosomal, and genome levels.

• Individual genes from different species can be sequenced and compared.

Introduction to PCR from Access Excellence

Review the PCR lecture from earlier this semester

Jurassic Park dinosaurs from mosquito DNA from amber? From the UK Natural History Museum

• These genes can come from the nuclear, mitochondrial, or chloroplast genomes.

• Mitochondrial DNA is maternally inherited (and has been used to trace human origins).

• Becoming Human With Don Johansen

• Dr. Stanley Ambrose, UIUC

• We almost went extinct From Prehistoric Life, BBC

• Human evolution and a botleneck 71,000 years ago.

• Chromosome banding patterns and protein sequences can also be compared.

• PCR and DNA sequencing is used to compare DNA sequences to determine the evolutionary relationships among organisms.

• 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, Text fig. 18.16, pg 338.

• A phylogeny of humans and relatives, Text fig. 18.15, pg 338.

• A "modern" application - Thomas Jefferson and Sally Hemmings

• Neanderthal DNA Sequenced

• Neanderthal Genome Project

• A Breed Apart DNA Tests: Humans Not Descended from Neanderthals

• Blow to Neanderthal breeding theory from The BBC

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.