1. Ch 12
Evidence of evolution

2. 12.1 Clues to evolution lie in the Earth, body structures, and molecules
Paleontology is the study of fossil remains.
Scientists think the Earth is 4.6 billion years old.
The geologic time scale divides Earth’s history into a series of era’s defined by major geologic or biological events. (like mass extinctions)
12.2 A fossil is any evidence of an organism from more than 10,000 years ago
A. Ways fossils form- compression, petrification, impression, cast, intact preservation.

4. B. The fossil record is often incomplete
A. three explanations for why the fossil record is incomplete
1. Most organisms never leave a fossil trace
2. Erosion or movements of the tectonic plates destroy some fossils that did form.
3. Many that are deep in the earth may not be discovered.

5. C. The age of a fossil can be estimated in two ways
A. Relative dating means(not dating your relatives)- not specific and based on the principle of superposition. Basically, puts fossils in a general age based on the layer of rock they are in. Deeper layer=older fossil.
B. absolute dating- test the fossil or the soil surrounding it- expressed MYA. Gives a range of ages(not as exact as the name implies)
Radioactive decay- uses the half-life of known radioactive isotopes to date a fossil. Common isotopes used are C14 and K40

6. 12.3 Biogeography considers species’ geographical locations
Biogeography is the study of distribution of species across the planet.
A. the theory of plate tectonics explains earth’s shifting continents.
Plate tectonics is the idea that the earth’s surface is broken up into large plates that shift and move due to forces within the Earth.
B. Species distributions reveal evolutionary events-
Marsupials are pouched mammals that are born hairless and blind- they were once the most abundant mammals on the planet.
Placental mammals develop inside the mother longer so they are born more developed(an evolutionary advantage) they have replaced most marsupials over time.
Marsupials persisted in South America, long after they were displaced on most continents- but when the isthmus of Panama formed, this allowed placental mammals to invade and replace them. This illustrates biogeography.

7. Island biogeography
Is a small scale application of biogeography studying the distribution of species on island chains.
Wallace’s line is a deep water trench that explained unique species of birds and mammals populating different islands. The trench kept them from migrating and having similar species on the islands.

9. 12.4 anatomical comparisons may reveal common descent
A. homologous structures have similarities due to common ancestry. An example is the vertebrate skeleton.
The skeleton of vertebrates provide support, made of the same material and consist of many of the same parts.

10. B. Vestigial structures
Structures that has no apparent function in one species, but it is homologous to a functioning structure or organ in another species.
Examples in humans- muscles that make the hair on your body stand up, tails in embryos, ear muscles.
C. convergent evolution produces superficial similarities
Analogous structures have a similar function, but evolved separately- (homologous structures show common ancestry)
Convergent evolution produces similar adaptations in organisms that do not have shared ancestors- examples- loss of pigmentation in cave animals, sharks and dolphins

11. 12.5 Embryonic development patterns provide evolutionary clues
The science of studying embryonic development is controversial because Ernst Haeckel altered drawings of different vertebrates as embryos to make them look more similar.
This caused people to distrust the science.
A new field that has developed since the discovery of genes that contribute to development is called evolutionary development biology.
One goal of this field is to identify these genes and determine how mutations can give rise to new body forms.
Homeotic is a general term that describes any gene that when mutated, leads to organisms with structures in abnormal or unusual places.

12. Homeotic genes
This fruit fly has a mutation that has caused a leg to grow where an antennae should be.

13. 12.6 Molecules reveal relatedness
Nucleic acids and proteins are molecules that are most useful to evolutionary biologists.
A. Comparing DNA and protein sequences may reveal close relationships:
The underlying assumption of molecular evolution is that the greater the similarity between two modern species, the closer the evolutionary relationship.
One advantage of molecular comparisons is that they are less subjective than deciding whether two anatomical structures are homologous or analogous.
DNA- is used to compare species by comparing entire genomes, looking at a few bases, one gene, or a family of genes with related structures.
They can sequence non-coding DNA and even though they don’t have a known function, this can imply common descent.
Analyzing DNA sequences can also reveal how evolution works.

14. Proteins- Two examples of proteins that scientists use to compare species are Keratin, and cytochrome c
B. Molecular clocks help assign evolutionary events-
Scientists must know the mutation rate for a gene, plus the number of differences in the DNA sequences for that gene in two species
A molecular clock estimates the time an organism diverged from a common ancestor.
For example, scientists estimate that humans and chimpanzees about 4 to 6 million years ago.
Tracking mitochondrial DNA is particularly useful because it’s molecular clock “ticks” 5 to 10 times faster than the nuclear DNA clock. MtDNA can also be extracted from extinct organisms. It is inherited from mother’s only, it doesn’t cross over so it can be used to trace a long history of evolution.