1. Evidence for Evolution
Topic 5.1

2. Understanding: Evolution occurs when heritable characteristics of a species change.
*There is evidence that characteristics of species change over time.
Acquired characteristics = develop after birth
Heritable characteristics = already present at birth
Evolution = change in heritable characteristics
Natural Selection = the mechanism of evolution
“evolution BY natural selection”

3. 3 types of evidence for evolution:
Fossil record
Selective breeding of domesticated animals
Homologous structures

4. Understanding: Fossil record provides evidence for evolution

5. Paleontology = study of fossils

6. Evidence for evolution from fossil record:
Rock layers are deposited from the bottom up
Therefore we can determine RELATIVE AGE of fossils
We can also determine ABSOLUTE AGE of fossils through radioisotope dating (such as carbon dating) of the rocks
In rock layers from bottom up: bacteria, algae, fungi, worms, bony fish, amphibians, reptiles, birds, mammals (110 mya)
Plant fossils occur before animal fossils
Extensive sequence of fossils, linking related organisms together

7. Trilobites! Extinct species of marine arthropods
First appeared in early Cambrian era (521 mya), flourished during Paleozoic era, completely extinct by Permian era (250 mya)
One of most successful animals, living in ocean for over 250 my
Over species

8. Missing Links! “missing links” = gaps in fossil record
E.g. link between reptiles and birds
Dilong paradoxus = feathered dinosaur
“emperor dragon paradox”
Fossil found in China
Lived 130 mya
5 ft tall, 25 pounds

9. Understanding: selective breeding of domesticated animals shows that artificial selection can cause evolution
Domesticated breeds of livestock and pets have not always existed in their current form
Artificial selection = the process of humans repeatedly selecting for and breeding animals and plants with traits most suited for or desired by humans
Artificial selection causes considerable changes in domesticated animals over relatively short period of time
Shows that “selection” can cause evolution (but doesn’t prove evolution has actually occurred through “natural” selection)

10. Over the last 15,000 yrs many breeds of dog have been developed by artificial selection from domesticated wolves

11. Artificial Selection examples:

12. Where did all these similar veggies come from?

13. Understanding: evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function

14. Convergent vs Divergent evolution

15. Adaptive radiation
= a process in which organisms diversify rapidly into many new forms, particularly when a change in the environment makes new resources available, creates new challenges and opens environmental niches.

16. …homologous structures
Do not prove organisms evolved
Do not prove common ancestry
Do not explain the mechanism of evolution
But they are difficult to explain without evolution
E.g. why do we have an appendix? Could be explained by evolution as something no longer with a function and is gradually being lost.

17. Nature of Science: looking for patterns, trends & discrepancies: there are common features in bone structure of vertebrate limbs despite their varied use
* Varied use of vertebrate limbs: walking, running, jumping, flying, swimming, grasping, digging, tearing
* Varied uses require different joints, different amounts of force, different features
* However, there is a pattern: common bone structure despite different functions!
* The pattern: pentadactyl limbs
* Patterns require explanation
* Only reasonable explanation
proposed so far is evolution from
a common ancestor

18. Application: Comparison of the pentadactyl limb of mammals, birds, amphibians & reptiles with different methods of locomotion

19. Understanding: populations of a species can gradually diverge into separate species by evolution
Species = a group of organisms which can interbreed and produce fertile offspring
Speciation = evolutionary process by which new species arrive
How?
Two populations of same species separate (geographically or biologically)
Natural selection acts differently on the two, so they evolve in different ways (they diverge)
3. After time, if they can no longer interbreed, they are 2 different species

20. Here’s a speciation example from U of Cal at Berkeley:

21. The scene: a population of wild fruit flies minding its own business on several bunches of rotting bananas, cheerfully laying their eggs in the mushy fruit...

22. Disaster strikes: A hurricane washes the bananas and the immature fruit flies they contain out to sea. The banana bunch eventually washes up on an island off the coast of the mainland. The fruit flies mature and emerge from their slimy nursery onto the lonely island. The two portions of the population, mainland and island, are now too far apart for gene flow to unite them. At this point, speciation has not occurred—any fruit flies that got back to the mainland could mate and produce healthy offspring with the mainland flies.

23. The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does. Morphology, food preferences, and courtship displays change over the course of many generations of natural selection.

24. So we meet again: When another storm reintroduces the island flies to the mainland, they will not readily mate with the mainland flies since they’ve evolved different courtship behaviors. The few that do mate with the mainland flies, produce inviable eggs because of other genetic differences between the two populations. The lineage has split now that genes cannot flow between the populations.

25. Allopatric vs Sympatric speciation
Allopatric speciation = species separated geographically, then become 2 different species
Sympatric speciation = species in same geographic location, but separated biologically into 2 diff groups because of 2 different preferences (habitat, diet, niche, etc), therefore reducing gene flow between the 2 groups until they are 2 different species

26. Sympatric or allopatric?

27. Endemic species = species found only in a certain geographical area
E.g. lava lizards are endemic to Galapagos Islands
(similar lizards on nearby islands, but diff species)
What are some endemic species to Florida?

28. Gradual vs Punctuated divergence?

29. Understanding: continuous variation across the geographical range of related populations matches the concept of gradual divergence
Continuous range of variation between populations = evidence for origin of new species by evolution
Willow ptarmigan of Norway vs red grouse of Britain

30. Continuous variation in Galapagos Finches

31. Application: development of melanistic insects in polluted areas.
Peppered moth activity
Melanistic = dark varieties of typically light-coloured insects
Biston betularia = peppered moth
Demonstrates changes in allele frequencies over time due to natural selection

32. Peppered moth example demonstrates changes in allele frequencies over time due to natural selection

33. Melanistic ladybugs! Where would they be more common?

35. There are many misconceptions!

36. Charles Darwin
Published Origin of Species by Means of Natural Selection in 1859
Throughout his book, he did not use the word “evolution”
Instead “decent with modification by means of natural selection”
Darwin used the word evolution one time, on the last line:
There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone circling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved. [Abridged version of Origin of Species]