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 by which descendants come to differ from ancestors.
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 & variation 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 of an individual compared to others in the same group
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

10. 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

11. Darwin observed fossil and geologic evidence supporting an ancient Earth.
Darwin found fossils of extinct animals that resemble modern animals
Darwin found marine fossil shells high up in the Andes mountains
Glyptodon Modern armadillo

12. He saw land move from underwater to above sea level during an earthquake
Darwin extended his observations to the evolution of organisms (gradual change leads to great change over time)

13. 10.3 – Theory of Natural Selection
Key Concept:
HOW DOES EVOLUTION OCCUR? Darwin proposed natural selection as a mechanism for evolution.

14. 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

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17. There is a struggle for survival due to overpopulation and limited resources
Darwin proposed that adaptations arose over many generations

18. 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 & reproduce better than other individuals it competes against
Fitness: ability to survive and reproduce
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

19. 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

20. 10.4 – Evidence of Evolution
Key Concept:
Evidence of common ancestry among species comes from many sources.

21. 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 nitrogen-14)
Pro: can give an accurate age
Con: can’t give an age for really old fossils (if all isotopes have decayed)

23. Biogeography
Island species most closely resemble nearest mainland species
Populations can show variation from one island to another
Example: Darwin’s finches

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

26. 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.

27. 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

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

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

30. 11.1 – Genetic Variation Within Populations
Key Concept:
A population shares a common gene pool.

31. 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 of all individuals 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.

33. 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

34. 11.2 – Natural Selection in Populations
Key Concept:
Populations, not individuals, evolve.

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

36. Directional Selection
Favors phenotypes at one extreme

37. Stabilizing Selection
Favors the intermediate phenotype

38. Disruptive Selection
Favors both extreme phenotypes

40. 11.3 – Other mechanisms of Evolution
Key Concept:
Natural selection is not the only mechanism through which populations evolve.

41. 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

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

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

44. Sexual selection occurs when certain traits increase mating success.
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

45. 11.5: Speciation through Isolation
Key Concept: New species can arise when populations are isolated.

46. 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)

47. 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.

48. 11.6 – Patterns in Evolution
Key Concept:
Evolution occurs in patterns.

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

50. 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

51. 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

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