1. Evolution

2. 10.1 – Early Ideas About Evolution  Key Concept  There were theories of biological and geologic change before Darwin.

3. Early scientists proposed ideas about evolution.  Evolution is the biological change over time.  A species is a group of organisms that can reproduce and have fertile offspring.

4. Theories of geologic change set the stage for Darwin’s theory.  There were three theories of geologic change:  Catastrophism: natural disasters such as floods and volcanic eruptions have shaped landforms and caused species to become extinct.  Gradualism: changes in landforms resulted from slow changes over a long period of time  Uniformitarianism: the geologic processes that shape Earth are uniform through time

5.  Uniformitarianism is the prevailing theory of geologic change.

6. 10.2 – Darwin’s Observations  Key Concept:  Darwin’s voyage provided insight on evolution.

7. Charles Darwin  Known as the father of evolution  Traveled around the world on the HMS Beagle  Observed geological phenomena and adaptations in species  Published findings in his book Origin of Species  1800’s

8. Darwin observed differences among island species.  Variation: difference in a physical trait  Galapagos tortoises that live in areas with tall plants have long necks and long legs  Galapagos tortoises that live in areas with low plants have short necks and short legs  Galapagos finches (Darwin’s finches) that live in areas with hard-shelled nuts have strong beaks  Galapagos finches that live in areas with insects/fruit have long, thin beaks

9.  Adaptation: feature that allows an organism to better survive in its environment  Species are able to adapt to their environment  Adaptations can lead to genetic change in a population

10. Darwin observed fossil and geologic evidence supporting an ancient Earth.  Darwin found fossils of extinct animals that resemble modern animals  Darwin found fossil shells high up in the Andes mountains GlyptodonModern armadillo

11.  He saw land move from underwater to above sea level during an earthquake  Darwin extended his observations to the evolution of organisms

12. 10.3 – Theory of Natural Selection  Key Concept:  Darwin proposed natural selection as a mechanism for evolution.

13. Several key insights led to Darwin’s idea for natural selection.  Natural selection: mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals  Artificial selection : process by which humans change a species by breeding it for certain traits.  Heritability: ability of a trait to be passed down  There is a struggle for survival due to overpopulation and limited resources  Darwin proposed that adaptations arose over many generations

14. Natural selection explains how evolution can occur.  Variation: heritable differences that exist in every population are the basis for natural selection  Overproduction: Having many offspring increases the chance of survival but also results in competition for resources  Adaptation: certain variation that allows an individual to survive better than other individuals it competes against  Descent with modification: Heritability of adaptations. More individuals will have the trait in every following generation, as long as the environmental conditions remain beneficial for the trait  Fitness: ability to survive and reproduce

15. Natural selection acts on existing variation.  Natural selection can act only on traits that already exist.  New alleles (leading to new phenotypes) are not made by natural selection – they occur by genetic mutations.  Structures take on new functions in addition to their original function. wrist bone five digits

16. 10.4 – Evidence of Evolution  Key Concept:  Evidence of common ancestry among species comes from many sources.

17. Fossils & the Fossil Record  Shows how species changed their form/shape over time  Ways of dating fossils:  Relative dating: estimates the age of fossils by comparing fossil to others in the same layer of rock  Pro: can be used if there is no other way to tell the age of the fossil  Con: layers of rock can be shifted by natural events (earthquakes, mudslides, etc.) and this can mess up estimate  Radiometric dating: uses the decay of radioactive isotopes (carbon- 14 changes into carbon-12)  Pro: can give an accurate age  Con: can’t give an age for really old fossils (if all isotopes have decayed)

19. Biogeography  Island species most closely resemble nearest mainland species  Populations can show variation from one island to another  Example: rabbit fur vs. climate; Darwin’s finches

20. Embryology  Similar embryos, diverse organisms  Identical larvae, diverse adult body forms  Gill slits and “tails” as embryos Larva Adult barnacle Adult crab

21. Homologous Structures  Similar in structure, different in function  Evidence of a common ancestor  Example: bones in the forelimbs of different animals (humans, cat legs, whale fins, bat wings)  Not to be confused with analogous structures – those that have similar functions but are not made of similar structures. Not evidence of a close evolutionary relationship. Example: bat wings, insect wings.

22. Vestigial Organs/Structures  Remnants of organs or structures that had a function in an early ancestor but have lost their function over time  Evidence of a common ancestor  Examples:  Human appendix & tailbone  Wings on flightless birds (ostrich, penguins)  Hindlimbs on whales, snakes

23. Molecular Biology  Common genetic code (A, T, C, & G)  Similarities in DNA, proteins, genes, & gene products  Two closely related organisms will have similar DNA sequences & proteins

24.  DNA fingerprints will also be very close if the species are closely related

25. 11.1 – Genetic Variation Within Populations  Key Concept:  A population shares a common gene pool.

26. Genetic variation in a population increases the chance that some individuals will survive.  Genetic variation leads to phenotypic variation  Necessary for natural selection  Genetic variation is stored in a population’s gene pool  Made up of all the alleles in a population  Allele combinations form when organisms have offspring  Allele frequency: a measure of how common a certain allele is in a population. Can be impacted by natural selection.

27. Genetic variation comes from several sources.  Mutations  Can form a new allele  Passed to offspring if in a gamete  Recombination  Usually occurs during meiosis  Parents’ alleles rearranged during gamete formation

28. 11.2 – Natural Selection in Populations  Key Concept:  Populations, not individuals, evolve.

29. Microevolution  Evolution within a population  Observable change in allele frequencies  Can result from natural selection  Types:  Directional selection  Stabilizing selection  Disruptive selection

30. Directional Selection  Favors phenotypes at one extreme

31. Stabilizing Selection  Favors the intermediate phenotype

32. Disruptive Selection  Favors both extreme phenotypes

33. 11.3 – Other mechanisms of Evolution  Key Concept:  Natural selection is not the only mechanism through which populations evolve.

34. Gene Flow  Movement of alleles between populations  Occurs when individuals join new populations and reproduce  Their alleles become part of gene pool  Keeps neighboring populations similar  Low gene flow increases the chance that two populations will evolve into different species bald eagle migration

35. Genetic Drift  Change in allele frequencies due to chance  Causes a loss of genetic diversity  Common in small populations  Bottleneck Effect is genetic drift after a bottleneck event  Occurs when an event drastically reduces population size

36.  Founder Effect is genetic drift that occurs after the start of a new population  Occurs when a few individuals start a new population

37. Sexual selection occurs when certain traits increase mating success.  Sexual selection  Occurs due to higher cost of reproduction for females  Males produce sperm continuously  Females are more limited in potential offspring each cycle  Two types:  Intrasexual selection: competition among males  Intersexual selection: males display certain traits to females

38. 11.5: Speciation through Isolation  Key Concept: New species can arise when populations are isolated.

39.  If gene flow stops between two populations, they are said to be isolated.  Adaptations, mutation, and genetic drift may change the gene pools of the populations, and over time the populations may become more and more genetically different.  Reproductive isolation: when members of different populations can no longer mate successfully with one another.  This is the final step before speciation (the rise of two or more species from one existing species)

40.  Several kinds of barriers can prevent mating between populations, leading to reproductive isolation.  Behavioral isolation: differences in courtship or mating behaviors.  Geographic isolation: physical barriers that divide a population into two or more groups.  Temporal isolation: timing prevents reproduction between populations.

41. 11.6 – Patterns in Evolution  Key Concept:  Evolution occurs in patterns.

42. Species can become extinct.  Extinction: elimination of a species from Earth  Background extinction  Mass extinction

43. Background Extinction  Occur randomly, but at a low rate  Usually affect only a few species in a small area  Can by caused by local changes in the environment

44. Mass Extinction  Rare, but very intense  Can operate at a global level  Caused by a catastrophic event such as an ice age  At least 5 mass extinctions in the last 600 million years

45. Extinction  Species go extinct because they lack the variation needed to adapt