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Presentation on theme: "Evolution."— Presentation transcript:

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 Glyptodon Modern 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 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. 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

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)

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

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

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

40 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

41 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

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

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