210.1 – Early Ideas About Evolution Key ConceptThere were theories of biological and geologic change before Darwin.
3Early 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.
4Theories 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 timeUniformitarianism: the geologic processes that shape Earth are uniform through time
5Uniformitarianism is the prevailing theory of geologic change.
7Charles Darwin Known as the father of evolution Traveled around the world on the HMS BeagleObserved geological phenomena and adaptations & variation in speciesPublished findings in his book Origin of Species1800’s
8Darwin observed differences among island species. Variation: difference in a physical trait of an individual compared to others in the same groupGalapagos tortoises that live in areas with tall plants have long necks and long legsGalapagos tortoises that live in areas with low plants have short necks and short legsGalapagos finches (Darwin’s finches) that live in areas with hard-shelled nuts have strong beaksGalapagos finches that live in areas with insects/fruit have long, thin beaks
10Adaptation: feature that allows an organism to better survive in its environment Species are able to adapt to their environmentAdaptations can lead to genetic change in a population
11Darwin observed fossil and geologic evidence supporting an ancient Earth. Darwin found fossils of extinct animals that resemble modern animalsDarwin found marine fossil shells high up in the Andes mountainsGlyptodon Modern armadillo
12He 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)
1310.3 – Theory of Natural Selection Key Concept:HOW DOES EVOLUTION OCCUR? Darwin proposed natural selection as a mechanism for evolution.
14Several 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 individualsArtificial selection: process by which humans change a species by breeding it for certain traits.Heritability: ability of a trait to be passed down
17There is a struggle for survival due to overpopulation and limited resources Darwin proposed that adaptations arose over many generations
18Natural selection explains how evolution can occur. Variation: heritable differences that exist in every population are the basis for natural selectionOverproduction: Having many offspring increases the chance of survival but also results in competition for resourcesAdaptation: certain variation that allows an individual to survive & reproduce better than other individuals it competes againstFitness: ability to survive and reproduceDescent 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
19Natural 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 bonefive digits
2010.4 – Evidence of Evolution Key Concept:Evidence of common ancestry among species comes from many sources.
21Fossils & the Fossil Record Shows how species changed their form/shape over timeWays of dating fossils:Relative dating: estimates the age of fossils by comparing fossil to others in the same layer of rockPro: can be used if there is no other way to tell the age of the fossilCon: layers of rock can be shifted by natural events (earthquakes, mudslides, etc.) and this can mess up estimateRadiometric dating: uses the decay of radioactive isotopes (carbon- 14 changes into nitrogen-14)Pro: can give an accurate ageCon: can’t give an age for really old fossils (if all isotopes have decayed)
26Homologous Structures Similar in structure, different in functionEvidence of a common ancestorExample: 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.
27Vestigial Organs/Structures Remnants of organs or structures that had a function in an early ancestor but have lost their function over timeEvidence of a common ancestorExamples:Human appendix & tailboneWings on flightless birds (ostrich, penguins)Hindlimbs on whales, snakes
28Molecular Biology Common (universal) genetic code (A, T, C, & G) Similarities in DNA, proteins, genes, & gene productsTwo closely related organisms will have similar DNA sequences & proteins
29DNA fingerprints will also be very close if the species are closely related
3011.1 – Genetic Variation Within Populations Key Concept:A population shares a common gene pool.
31Genetic variation in a population increases the chance that some individuals will survive. Genetic variation leads to phenotypic variationNecessary for natural selectionGenetic variation is stored in a population’s gene poolMade up of all the alleles of all individuals in a populationAllele combinations form when organisms have offspringAllele frequency: a measure of how common a certain allele is in a population. Can be impacted by natural selection.
33Genetic variation comes from several sources. MutationsCan form a new allelePassed to offspring if in a gameteRecombinationUsually occurs during meiosisParents’ alleles rearranged during gamete formation
3411.2 – Natural Selection in Populations Key Concept:Populations, not individuals, evolve.
35Microevolution Evolution within a population Observable change in allele frequenciesCan result from natural selectionTypes:Directional selectionStabilizing selectionDisruptive selection
36Directional Selection Favors phenotypes at one extreme
37Stabilizing Selection Favors the intermediate phenotype
38Disruptive SelectionFavors both extreme phenotypes
4011.3 – Other mechanisms of Evolution Key Concept:Natural selection is not the only mechanism through which populations evolve.
41Gene Flow Movement of alleles between populations Occurs when individuals join new populations and reproduceTheir alleles become part ofgene poolKeeps neighboring populations similarLow gene flow increases the chance that two populations will evolve into different speciesbald eagle migration
42Genetic Drift Change in allele frequencies due to chance Causes a loss of genetic diversity in a populationCommon in small populationsBottleneck Effect is genetic drift after a bottleneck eventOccurs when an event drastically reduces population size
43Founder Effect is genetic drift that occurs after the start of a new population Occurs when a few individuals start a new population
44Sexual selection occurs when certain traits increase mating success. Occurs due to higher cost of reproduction for femalesMales produce sperm continuouslyFemales are more limited in potential offspring each cycleTwo types:Intrasexual selection: competition among malesIntersexual selection: males display certain traits to females
4511.5: Speciation through Isolation Key Concept: New species can arise when populations are isolated.
46If 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)
47Several 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.
4811.6 – Patterns in Evolution Key Concept:Evolution occurs in patterns.
49Species can become extinct. Extinction: elimination of a species from EarthBackground extinctionMass extinction
50Background Extinction Occur randomly, but at a low rateUsually affect only a few species in a small areaCan by caused by local changes in the environment
51Mass Extinction Rare, but very intense Can operate at a global level Caused by a catastrophic event such as an ice ageAt least 5 mass extinctions in the last 600 million years
52ExtinctionSpecies go extinct because they lack the variation needed to adapt