EvolutionChapter 15
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““Nothing in Nothing in biology biology
makes sense makes sense EXCEPT in the EXCEPT in the
light of light of evolution.” evolution.” Theodosius Theodosius DobzhanskyDobzhansky
Evolution
Charles Darwin in later yearsCharles Darwin in later years
15-1Darwin’s Theory
of Natural Selection
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Early Ideas On Earth’s Organisms
• Aristotle believed species were fixed creations arranged by their complexity
• Idea lasted 2000 years
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Contributor’s to Darwin’s thinking included:
•Charles Lyell –geologic processes still changing Earth – (Principles of Geology book)
•Georges Cuvier – species extinction (Catastrophism)
•Thomas Malthus – struggle for existence (resources)
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Contributor’s to Darwin’s thinking included:
• James Hutton - Gradualism• John Baptiste Lamarck –
developed idea of change over time. Inheritance of Acquired Characteristics and Law of Use and Disuse
•Alfred Russel Wallace – organisms evolved from common ancestors
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Lamarck’s Theory of Evolution
• Law of Use and Disuse
• If a body part were used, it got stronger
• If body part was NOT used, it dissappeared
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Lamarck’s Theory of Evolution• Inheritance Of Acquired
Traits– Traits Acquired During Ones
Lifetime Would Be Passed To Offspring
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Clipped ears of dogs could be passed to offspring!
Lamarck’s Mistakes
• Lamarck Did NOT Know how traits were inherited (Traits are passed through genes)
• Genes Are NOT Changed By Activities In Life
• Change Through Mutation Occurs Before An Organism Is Born
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Charles Darwin the Naturalist
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Voyage of the BeagleCharles Darwin• Born Feb. 12,
1809• Joined Crew of
HMS Beagle, 1831• Naturalist• 5 Year Voyage
around world• Avid Collector of
Flora & Fauna• Astounded By
Variety of Life12
Darwin’s Voyage of Discovery
13A reconstruction of the HMS Beagle sailing off Patagonia.A reconstruction of the HMS Beagle sailing off Patagonia.
Darwin Left England in 1831
14Darwin returned 5 years later in 1836Darwin returned 5 years later in 1836
The Galapagos Islands• Small Group of Islands 1000
km West of South America
• Similar Climates• Animals On Islands Unique
•Tortoises•Iguanas•Finches•Mockingbirds
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The Galapagos Islands• Volcanic islands off the coast of South America
• Island species varied from mainland species & from island-to-island species
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The Galapagos Islands• Finches on the islands resembled a
mainland finch• More types of finches appeared on
the islands where the available food was different (seeds, nuts, berries, insects…)
• Finches had different types of beaks adapted to their type of food gathering
• Mockingbirds had different traits suited for their niche!
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Darwin’s Observations• Patterns of
Diversity were shown
• Unique Adaptations in organisms
• Species Not Evenly Distributed
•Australia, Kangaroos, but No Rabbits
•S. America, Llamas
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Darwin’s Observations
•Both Living Organisms & Fossils collected
•Fossils included:
•Trilobites•Giant Ground Sloth of South America
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This species NO longer existed.This species NO longer existed. What had happened to them?What had happened to them?
Definition
•Evolution is the slow, gradual change in a population of organisms over time
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Darwin’s Observations• Left unchecked, the
number of organisms of each species will increase exponentially, generation to generation
• In nature, populations tend to remain stable in size
• Environmental resources are limited
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Darwin’s Conclusion• Production of more
individuals than can be supported by the environment leads to a struggle for existence among individuals
• Only a fraction of offspring survive each generation
• Survival of the Fittest
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Darwin’s Observations• Individuals of a
population vary extensively in their characteristics with no two individuals being exactly alike.
• Much of this variation between individuals is inheritable. 25
Darwin’s Conclusion• Individuals who
inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals
• Called Natural Selection
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•The unequal ability of individuals The unequal ability of individuals to survive and reproduce leads to to survive and reproduce leads to a gradual change in a population, a gradual change in a population, with favorable characteristics with favorable characteristics accumulating over generations accumulating over generations (natural selection)(natural selection)•New species evolveNew species evolve
Darwin’Darwin’s s
Theory Theory of of
EvolutioEvolutionn
Natural Variation and Artificial Selection
• Abandoned The Idea That Species Were Perfect & Unchanging
• Observed Significant Variation in All Species Observed
• Observed Farmers Use Variation To Improve Crops & Livestock
• Called Selective Breeding
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Natural Variation and Artificial Selection
•Natural Variation– Differences Among
Individuals Of A Species
•Artificial Selection– Selective Breeding To
Enhance Desired Traits Among Stock or Crops
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Natural Selection•4 Principles of Natural Selection:
•1. Variation•2. Heritability•3.
Overproduction•4. Reproductive
Advantage31.
Natural Selection Concepts
• The Struggle for Existence (compete for food, mates, space, water, etc.)
• Survival of the Fittest (able to survive and reproduce)
• Descent with Modification (new species arise from common ancestor replacing less fit species)
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Survival of the Fittest• Fitness
– Ability of an Individual To Survive & Reproduce
• Adaptations Can Be:– Physical
•Speed, Camouflage, Claws, Quills, etc.
– Behavioral•Solitary, Herds, Packs, Activity, etc.
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Natural Selection
•Cannot Be Seen Directly• It Can Only Be Observed
As Changes In A Population Over Many Successive Generations– Radiation– Fossil Record
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Evidence for Evolution – Evolution Observed
Selection against small guppies results in an increase in average size
Descent With Modification•Takes Place Over Long
Periods of Time•Natural Selection Can Be
Observed As Changes In– Body Structures– Ecological Niches– Habitats
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Descent With Modification•Species Today Look
Different From Their Ancestors
•Each Living Species Has– Descended– With Changes– From Other Species– Over Time
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Descent With Modification
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Descent With Modification
• Implies– All Living Organisms Are Related– Single Tree of Life
•DNA, Body Structures, Energy Sources
• Common Descent– All Species, Living & Extinct,
Were Derived From Common Ancestors
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Theory of Evolution Today
Supporting Evidence15-2
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Evidence of EvolutionKey Concept
Evidence For This Process Could Be Found In:
– The Fossil Record– The Geographical Distribution of
Living Species– Homologous Structures of Living
Organisms– Similarities In Early
Development41
Fossil Record
• Earth is Billions of Years Old• Fossils In Different Layers of
Rock (sedimentary Rock Strata) Showed Evidence Of Gradual Change Over Time
• Derived Traits – newly evolved features
• Ancestral Traits – old features
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Evidence for Evolution – The Fossil RecordEvidence for Evolution – The Fossil Record
Geographic Distribution of Living Species
• Different Animals On Different Continents But Similar Adaptations To Shared Environments
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Homologous Body Structures• Scientists Noticed Animals
With Backbones (Vertebrates) Had Similar Bone Structure
• May Differ In Form or Function
• Limb Bones Develop In Similar Patterns
•Arms, Wings, Legs, Flippers
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Homologous Body Structures
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Homologous StructuresHomologous Structures
Vestigial Body Structures• Not All Serve Important
Functions– Vestigial Organs
•Appendix In Man•Legs On Skinks or Leg Bones on
Snakes
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Analogous Structures
• Used the same but was not made the same way.
• Bird wings versus insect wings
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Similarities In Early Development
• Embryonic Structures Of Different Species Show Significant Similarities
• Embryo – early stages of vertebrate development
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Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
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Chicken Turtle
Rat
Human Fetus – 5 weeks
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Similarities in DNA Similarities in DNA SequenceSequence
Adaptations• Camouflage• Mimicry• Antimicrobial
Resistance
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Evolutionary Time Scales
Macroevolution: Long time Long time scale events scale events
that create and that create and destroy destroy species.species.
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Microevolution:
Short time scale events
(generation-to-generation) that
change the genotypes and phenotypes of
populations
Evolutionary Time Scales
Shaping Evolutionary Theory
15-3• Population Genetics
– Hardy-Weinberg Principle – genetic equilibrium (constant frequencies over time)
– p + q = 1 – allele frequency– p2 + 2pq + q2 = 1 – genotypic
frequency– Table 15.3 (page 432)
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Mechanisms of Evolution• Genetic Drift• Founder Effect• Bottleneck• Gene Flow• Nonrandom Mating• Mutation• Natural Selection
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Genetic Drift
• In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals. The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals. That, in a nutshell, is genetic drift. It happens to ALL populations—there’s no avoiding the vagaries of chance.
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Founder Effect• A founder effect occurs when a new colony is started by a few
members of the original population. This small population size means that the colony may have:– reduced genetic variation from the original population.– a non-random sample of the genes in the original
population.– Example, the Afrikaner population of Dutch settlers in South
Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events.
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Bottleneck• Population bottlenecks occur
when a population’s size is reduced for at least one generation. Because genetic drift acts more quickly to reduce genetic variation in small populations, undergoing a bottleneck can reduce a population’s genetic variation by a lot, even if the bottleneck doesn’t last for very many generations. This is illustrated by the bags of marbles shown above, where, in generation 2, an unusually small draw creates a bottleneck.
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The elephant seal population was bottlenecked due to hunting in the 1890s.
Gene Flow• Some individuals
from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.
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Nonrandom Mating• Sexual Selection – individuals choose
mates based on certain traits.
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Mutation
• A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make the genes for brown beetles more frequent in the population.
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Natural Selection
• There is variation in traits.
• There is differential reproduction.
• There is heredity.
• One trait tends to become more common.
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Types of Selection
• 3 types of Natural Selection:– Stabilizing - average– Directional – one extreme– Disruptive – both extremes
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Reproductive Isolation• Prezygotic
– Habitat isolation– Temporal isolation– Behavioral isolation– Mechanical
isolation– Gametes die
• Postzygotic– Zygote dies– Hybrids sterile– Hybrids inviability– Low hybrid fitness 68
Speciation• Allopatric – due to geographic isolation. Isolation might occur because of great distance or a physical barrier, such as a desert or river
• Sympatric - Merely exploiting a new niche may automatically reduce gene flow with individuals exploiting the other niche. This may occasionally happen when, for example, herbivorous insects try out a new host plant.
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Patterns of Evolution
• Divergent Evolution– Adaptive radiation
• Coevolution– Predator/prey and
parasite/host – Competitive species – Mutualistic species
• Convergent Evolution– Analogous features– Bird and bat wings
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