an introduction to evolutionary biology
DESCRIPTION
Table of Contents What is Evolution? History and Development of a Unifying Discipline Latin America and Evolutionary Biology Taxonomy, Classification, and Species Mechanisms of Genetic Variation and Earth’s Diversity Select Topics in Evolutionary BiologyTRANSCRIPT
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AN INTRODUCTION TO EVOLUTIONARY BIOLOGYAcadec Super Quiz 2008-2009
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Table of Contents What is Evolution?
History and Development of a Unifying Discipline
Latin America and Evolutionary Biology Taxonomy, Classification, and Species Mechanisms of Genetic Variation and
Earth’s Diversity Select Topics in Evolutionary Biology
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What is Evolution?
In this section:o Evolution and the Nature
of Scienceo The Rise of Evolutionary
Biologyo The Development of
Evolutionary Theoryo Modern Synthesis
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Evidence for Evolution
Paleontologists study fossils that give clues to evolutionary processes
Tiktaalik is one such fossil (early tetrapod)
Many other scientific fields support the theory of evolution
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Evolution and Biology
• Evolution provides an explanation for the diversity of life
• The passing down of traits is now explained by both evolution and genetics
• Mutations and natural selection change populations across multiple generations
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Small and Large Evolutionary Changes
Evolution produces small-scale changes over short periods of time Example: Bacteria with antibiotic resistance
Large-scale changes occur over longer periods of time (speciation)
Speciation and other large-scale changes can help organisms inhabit new environments Example: The amniotic egg
Transitions like these, both large and small, can be found in the fossil record
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Evolution in Various Fields
Medicine: genetic analysis of SARS virus
Agriculture: artificially selecting wheat for preferred traits
Industry: selecting molecules for preferred traits
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Accepting Evidence of Evolution
Science relies on natural phenomena and testable explanations
Some see the differing natures of science and religion as being in conflict
Many scientists and theologians find no conflict They can reconcile the two explanations of
the world Evolution is still considered a theory, but
has been widely accepted as a fact
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Descent with Modification
• Dobzhansky says, “nothing in biology makes sense except in the light of evolution”
• Evolution means change between generations, or “descent with modification”
• A lineage is dependent on an ancestor-descendent relationship
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Adaptation
Adaptation is “design” in living things
Adaptation allows organisms to survive and reproduce
Examples include the woodpecker’s beak and camouflage
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Evolution Before Darwin
Jean-Baptiste Lamarck wrote Philosophic Zoologique in 1809
Lamarck argued that animals “strived” to adapt (in place to natural selection)
Others before Darwin believed in species fixity The idea that species never
change
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Charles Darwin’s Arrival and Reception
After his voyage on the Beagle (1832-37), Darwin failed to reconcile all current theories with the concept of adaptation
Darwin created his own theory, which included the concept of natural selection; Alfred Wallace also arrived at this conclusion on his own
Darwin and Wallace presented their findings in 1858
The theory seemed to contradict the Bible and was controversial among laymen, but was somewhat less so among scientists
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Flaws in the Theory of Evolution
• Darwin’s theory of evolution lacked a means of heredity, meaning that there was no mechanism to explain the passing down of traits
• Natural selection insufficiently explained intermediate forms in evolution (like proto-wings), which were seen as better explained by directed variation
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Mendelian Genetics
Gregor Mendel explained how traits were passed down from one generation to the next
His pea plant experiments (1856-63) explored concepts of hybridization, and dominant and recessive phenotypes
Mendel mailed his findings to Darwin, who never looked at them
A rediscovery of Mendelian inheritance in the early 1900s led to a marriage between that theory and Darwin’s theory of evolution
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The Modern Synthesis
• Fisher, Haldane, and Wright all published materials supporting a connection between Darwinian evolution and Mendelian genetics
• Combined with natural selection, Mendelian inheritance answered all the questions initially raised in 1858
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Further Development of Evolutionary Biology
Dobzhansky, Ford, Kettlewell, Mayr, Huxley, and many others published materials on genetics and evolution
The concepts of genotypes and gene pools were incorporated into the new way of thinking
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Pre-Darwinian Evolutionary Thought
• Ancient Greeks had theories on evolution
• James Ussher calculated the earth’s age to be roughly 6,000 years old according to Genesis
• Hutton, Lyell, Linnaeus, Buffon, E. Darwin, W. Smith, Werner, Cuvier, and Lamarck all contributed to evolutionary theory
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Darwin and the Wallace-Darwin Theory
1. Adaptation2. Variation3. Over-
reproduction4. Natural
selection
1. Variability in traits2. Over-reproduction3. Variability in fitness4. Fitness determines
success5. Heritable traits and
change between generations
Darwin’s Theory The Wallace-Darwin Theory
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Concepts in the Modern Synthesis
Genetic definition of evolution: “changes in allele frequencies within populations”
Alleles are different versions of the same gene
Sources of these changes include genetic drift (random changes), gene flow (exchanges between populations), mutation pressure (copying errors in genetic replication), and natural selection (“survival of the fittest”)
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Darwin and the Galapagos
In this section:o The Voyage of the HMS
Beagleo Chapter XVII: Galapagos
Archipelago (excerpt from Darwin’s journal)
o Adaptive Radiation of Darwin’s Finches
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Darwin’s Background
Raised in the Anglican Church
Loved science, went to medical school (1825)
Dropped out after witnessing surgery on a child with no anesthesia
Joined Christ’s College at Cambridge to study religion and pursue science in his spare time
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Before, During, and After the Beagle Two watershed events for Darwin: he re-read his
grandfather’s book and later witnessed his professor, Adam Sedgwick, making a scientific error
Professor Henslow recommended Darwin for the Beagle
Darwin got along with Captain FitzRoy most of the time
During the voyage, Darwin collected many specimens of flora and fauna
Back in England, he married and had 10 children Darwin returned in poor health and stayed that way
until his death in 1882
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The Voyage of the Beagle
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Darwin’s Journal: Introduction
The text in the guide has been condensed
He gives credit to Owen, Waterhouse, Gould, Jenyns, and Bell for influencing his work
He thanks several colleagues, especially Professor John Henslow, who helped him (from London) during the voyage
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The Galapagos
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September 15th-23rd
There are ten Galapagos islands, all south of the Equator, spotted with many craters, and volcanic in origin
Chatham Island had relatively few plants, only giant tortoises and some dull-colored birds
Charles Island had been frequented by buccaneers and whalers, now inhabited by political exiles and others
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September 29th
Darwin visited Albemarle Island and Narborough Island
Both were covered with black lava formations and much of the islands was sterile
There were black lizards on Albemarle, as well as yellow-brown ones
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October 8th – James Island
Darwin came across a group of Spaniards, as well as other small groups
Darwin learned that tortoise meat can be prepared a number of ways, and also visited a salina
Measured the temperature in various instances: the sand was at least 137º F
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Mice, Land Birds, and Water Birds
Mus Galapagoensis was the only indigenous terrestrial mammal (and mouse)
Darwin caught 26 land birds, 25 of which were unique to the archipelago
He also caught 11 water birds, only 3 of which were new species
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Reptiles – the Tortoise
Darwin discovered snakes, lizards, tortoises, and sea turtles
He was surprised to find no toads or frogs at all, even though the environment seemed ideal for them (perhaps egg differences?)
Tortoises travel to water sources, sometimes four miles a day
The inhabitants believed the tortoises to be deaf
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Galapagos Lizards
Aquatic: lives on rocky sea beaches
About a yard long Eats only seaweed When frightened, it will
allow itself to be captured rather than jump in the ocean
When thrown in, it will come out and return to the previous spot
Terrestrial: lives in burrows
Confined to the central islands
Smaller than the aquatic ones
Eats cactus and other vegetation
Will fight another lizard if held next to it
Amblyrhynchus cristatus Amblyrhynchus Demarlii
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Shells, Insects, and Plants
Darwin collected 90 shells, of which 47 were previously unknown
Also collected several insects, most of which were new species, but was surprised by how few there were
Collected 100 new species of flowering plants Was extremely surprised that fewer American
species of flora had not arrived at the islands through natural means, given the short distance between the two locations
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The Tameness of Birds
Darwin noted that birds were not afraid of humans
The birds could be killed from close range even after other birds had been killed nearby
Darwin believed this to mean that an instinct to avoid humans would have to be passed down through multiple generations
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Adaptive Radiation
Adaptive radiation is the diversification of populations into ecological niches
Four key concepts:1. Origins2. Speciation3. Diversity4. Disparity
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Finches and Speciation
Darwin’s finches are unique because of their rapid diversification and relative youth (3 MYA)
Allopatric speciation: geographic separation
Sympatry can lead to interbreeding with or without fitness loss or no interbreeding
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Environmental Factors
Sympatry is not required for speciation Not all islands might have existed when
speciation began A changing environment has significant effects
on adaptive radiation
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Adaptation and Reproductive Isolation 1977 drought:
populations of small finches decreased (no small seeds)
c. 1987 drought: populations of large finches decreased (no large seeds)
Dynamic equilibrium Medium ground finches respond to cues
from their own species even when genetically able to hybridize
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Finch Songs
Songs are learned traits passed down from parent to offspring
Songs are particular to populations, not necessarily entire species
Changes in environment can lead to natural selection of different songs than those of a parent species Some changes to songs are by chance, not
natural selection alone
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Adaptive Landscapes
Genotype and phenotype frequencies can be plotted on a 3D landscape to determine fitness
Areas of best fitness are known as peaks
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Adaptive Landscape and the River of Life
Genotype and phenotype frequencies can be plotted on a 3D landscape to determine fitness
Areas of best fitness are known as peaks
The river of life is a visual metaphor that may replace the tree of life (accuracy)
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Taxonomy, Classification, and Species
In this section:o Classificationo Taxonomy
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Taxonomy, Traditional Classification, and Cladograms
Aristotle, John Ray, Carolus Linnaeus, and Robert Whittaker all made significant contributions to taxonomy
Classifications from largest to smallest: Kingdom, Phylum, Class, Order, Family, Genus, Species
Traditional classification focuses on common ancestry and amount of divergence (major characters)
Cladograms focus on derived characteristics and incorporate parsimony
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Cladistics vs. Phenetics
Uses one or more derived characters
Focuses on lineages and common ancestry
Does not include overall similarity
Uses algorithms to determine similarity
Mathematical and objective
Not used very often, but helpful in objective studies
Cladistics Phenetics
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Nomenclature
According to the International Code of Botanical Nomenclature:1) All taxa belong to a higher taxonomic
group2) The first name for a new species to be
published is considered valid (the “dibs” rule)
3) All new taxa must have an author
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Definition of a Species
Unlike all other categories (e.g. Kingdom), species are not an artificial construct, and actually exist in nature
Reproductive compatibility typically defines a species (can these two animals have fertile offspring?)
Asexual reproduction and grey areas make this definition imperfect
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Nomenclature and Classification
Taxonomic keys help scientists determine which species an organism is
Evolution and lineages determine the closeness of relationships in classifying multiple organisms
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Example of Dichotomous Key
Dichotomous keys use technical language in simple steps to help classification
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Methods of Classification
Phenetics (numerical taxonomy) uses algorithms for an objective classification
Cladistics is the most popular and focuses on lineages
Evolutionary taxonomy is a combination of the two, but considered arbitrary by most scientists
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Kingdom Systems
Kingdoms, ranging in number from three to thirteen in some systems, are the largest taxonomic group
The most common is a five kingdom system, but it is being replaced by a six kingdom model
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Mechanisms of Genetic Variationand Earth’s Diversity
In this section: The Evidence for Biological
Evolution Evolutionary Mechanisms Introduction to Evolutionary
Biology On the Many Origins of
Species Speciation Standing in Place
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Contributions From Other Areas
Paleontology: fossils
Genetics: DNA Astrophysics and
geology: age of the earth
Physics and chemistry: dating methods
Anthropology: human origins
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Origins of the Universe and Earth
Georges Lemaitre: the Big Bang theory
Background radiation and distances allow for dating of the universe
Universe: 14 BYA Earth: 4.6 BYA Moon: 4.4-4.5 BYA
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Life’s Formation on Earth
Life is at least 3.5 billion years old
Life required three conditions to form: self-reproducing molecules (RNA?), enough molecules for variation, and heritable variations
Protocells with variations led to natural selection
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The Fossil Record
Newer sediment deposits are closer to the surface (and those fossils resemble modern organisms)
540 MYA: hard-bodied organisms begin to dominate the fossil record
Tiktaalik is a transitional form
Archaeopteryx: dinosaur-bird?
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Homologous and Analogous Structures
Homologous structures are morphological characteristics in multiple organisms that come from a single ancestral lineage (like human arms and dog forelimbs)
Analogous structures look similar but do not come from a common ancestral origin (like a dolphin’s and shark’s front fins/flippers)
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Evolution and Geographical Distribution
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Evolution and Geographical Distribution
Organisms live in so many different places because evolution (via adaptive radiation) produces a variety of life forms suited to ecological niches
Variations in precipitation levels, elevations, soils, and other factors lead to rapid speciation in colonizing species
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The Impact of DNA
DNA provides clues to past genetic changes According to genetic information, humans are closely
related to chimpanzees, but increasingly far from gorillas, mice, chickens, and puffer fish
DNA shows how much all life on Earth has in common
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The Impact of DNA
DNA provides clues to past genetic changes According to genetic information, humans are closely
related to chimpanzees, but increasingly far from gorillas, mice, chickens, and puffer fish
DNA shows how much all life on Earth has in common
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Humans and Chimps
Humans are 98% genetically identical to chimpanzees
In the case of one gene, all of the differences between humans and chimps (only 5 out of 250 nucleotides) could be matched on one side by gorilla DNA
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Human Evolution Timeline
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Evolutionary Mechanisms
Mutation, recombination, and gene flow increase genetic variation
Mutations can be beneficial, deleterious, or neutral
Genetic drift and natural selection decrease genetic variation
Natural selection can be directional, stabilizing, or disruptive
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Case Study: Manchester Moths
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The Evolutionary Process
Gene mutation leads to individuals being selected which leads to population evolution
Microevolution: gene mutations, small changes
Macroevolution: speciation, big changes
Abiogenesis is the theory of how living things first appeared (this is NOT evolution)
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Misconceptions
Morphological change and evolution are not always bound to one another
Tiny changes might be the environment acting on an organism, and not really evolution
Organisms act on the environment just as much as the environment acts on organisms
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Genetic Variation
Mutation types: deletion, duplication, inversion, insertion, translocation
Most animals are diploid (two alleles for every gene at each locus)
Homozygous: same alleles Heterozygous: two different
alleles Linkage disequilibrium alters
allele frequency
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Mating
Assortative mating creates a non-random distribution of alleles at a given locus
Non-random mating disrupts the Hardy-Weinberg equilibrium (allele frequencies)
Humans tend to mate with individuals of the same race, meaning there are fewer heterozygotes than predicted in the Hardy-Weinberg equilibrium
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Natural Selection
Sometimes heterozygotes are more fit than either homozygotes (malaria)
Reproductive success: direct, indirect, and inclusive fitness
Traits can end up used for something other than their original purpose This process is called
exaptation
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Sexual Selection
Fitness is not always related to being big, fast, or strong; reproductive success is more important
Females often select males based on secondary characteristics (peacock’s tail, flashes in fireflies)
These characteristics may reveal “good genes” or other desirable qualities in males
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Genetic Drift
Genetic drift is a random sampling error that occurs naturally in all sexually-reproducing populations
Mutations and genetic drift generally balance each other (mutations adding and drift subtracting)
Fisher and Wright disagreed on the importance of drift: Fisher said it had a negligible effect on large populations, while Wright said it was important in all populations
Unlike drift, the founder effect represents the remaining genetic material after a population “crash”
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Mutation and New Alleles
Most mutant alleles are neutral Some are harmful The smallest proportion are beneficial
Most new mutations are lost from the gene pool within one generation
Neutral mutations lost due to random drift, deleterious ones often selected against, and beneficial ones selected for (but still often lost)
Beneficial mutations happen less frequently but thrive most often
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Recombination and Gene Flow
Recombination is the mixing of maternal and paternal alleles during cell replication
It increases variation by shuffling genetic material
Gene flow is the addition of new genes via population mixing
Gene flow between distantly related species is horizontal transfer Horizontal transfer is rare
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Evolutionary Mechanisms – More
Genetic variation in a population is determined by the balance of mechanisms Natural selection can be positive or negative Genetic drift is random, so it cannot be positive or
negative Recurrent mutation of a beneficial allele will help it
reach fixation An allele that “catches a ride” with a beneficial allele
is a hitchhiker
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Evolutionary Theory and Genetics
Lamarck’s theory and Darwin’s studies are two early contributions to the new field
Mendel mailed Darwin his paper but Darwin never opened it
Mendel’s work was not accepted early on because he only studied discrete traits
Fisher’s Fundamental Theorem of Natural Selection states that adaptive change in a given population is proportional to the genetic variation present
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DNA and RNA
DNA nucleotides: adenine, guanine, cytosine, thymine
RNA: uracil instead of thymine; used in transcription
Introns do not code, exons do
Silent and replacement sites evolve at different rates
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Evolution and Development
Vestigial structures are traces of ancestry in modern animals Example: the human
appendix Common descent and
macroevolution are supported by the organization of traits (nested patterns of evolution)
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Speciation
Allopatric speciation occurs with geographic separation (most common)
Sympatric speciation (sometimes called microallopatric speciation) occurs without geographic separation
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Extinction
Normal extinction occurs for many reasons Competition, disappearing habitat, loss of
food source, etc. Mass extinction follows large-scale
events Asteroid impact, climate change, humans
Mass extinction is followed by huge periods of adaptive radiation because there are empty niches to fill Largest mass extinction: end of the Permian Most famous mass extinction: Cretaceous-
Tertiary boundary
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Punctuated Equilibrium
Punctuated equilibrium theory states that evolution is not a steady process Instead, long periods of
relatively little evolution and change are broken up by bursts of rapid change
Proposed by Stephen Jay Gould and Niles Eldredge
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Evolution’s Importance
Evolution unites disparate fields of biology
It explains the distribution of traits across multiple lineages and the variation of life on Earth
It helps explain how modern species came to be
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Rhagoletis: A Case Study
The apple maggot Rhagoletis is diverging into two species Speciation began without
geographic separation Cause appears to be mating
habitat preference (apple and hawthorn plants)
Studied first by Benjamin Walsh, then by Guy Bush
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Diversity in the Amazon
Speciation in the Amazon was originally thought to occur according to river separations
Research revealed that ancient ridges were responsible for some speciation
Mitochondrial DNA helped separate the two causes
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Sympatric Speciation and Frequency
Sympatric speciation is an explanation for speciation that occurs with no apparent physical separation Has occurred with other flies, fish, butterflies The theory is established; now the focus is on
how and why
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Sympatric Speciation Examples
Indigobirds – prefer mates that know the same song
Cichlids – exist at different depths within one lake
Palm Trees – initially separated by soil differences, now kept apart by flowering timing
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Sympatry: How Significant?
Some argue that the examples are still allopatric on a small scale
Others argue that sympatry exists but is very minor in the big picture of evolution
Some “clear cut” cases of allopatry are now attributed to sympatry
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Select Topics in Evolutionary Biology
In this section:o Jurassic
Genomeo Turn On: A
Revolution in the Field of Evolution?
o Evolution and Tinkering
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Genome Sizes
Big genomes are found in animals with big bone cells
Small genomes are found in animals with small bone cells
Junk DNA: non-coding material (98.5% of human DNA)
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Fossils and Genomes
Birds evolved from theropods, which had relatively small genomes This contradicted the assumption that
small genomes evolved with flight Genome sizes may be affected by
natural selection
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Embryos and Evolution
Recapitulation: “ontogeny recapitulates phylogeny”
Two kinds of change Through a lifetime Through a lineage
Is embryonic development a small-scale model of evolution?
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Evo Devo’s Findings
Evo Devo is short for evolutionary developmental biology
All animals are built from essentially the same genes (including Hox genes)
Differences in animals are caused by the same genes expressed at different times and places
Evolution is mostly a matter of “throwing switches”
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“Throwing Switches”
Gene expression, not gene presence, is the guiding force of evolution
Secret to this might lie in the non-coding or “junk” DNA This may explain the
wide variation of life with so few genes
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Evo Devo: A Revolution?
Evo devo may be more of a paradigm shift than a revolution
Darwin’s theory of evolution and Mendel’s theory of inheritance were revolutions
Evo devo is not quite as significant a breakthrough, but still important
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The Nature of Science Science follows a
method Hypotheses have to
be testable Science gives
provisional answers to limited questions
Religion and mythology can offer comprehensive answers
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Hierarchy of Objects and Constraints
Sciences can be arranged in order of complexity (physics to psychosociology)
Successive integrations in nature: analyzing complex objects at all levels and determining predictability
Constraints and history dictate evolutionary systems
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Natural Selection
Natural selection is the result of two constraints Reproduction Ongoing interaction with the
environment Natural selection gives direction to
changes
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Natural Selection as a Tinkerer
Natural selection is not an engineer Engineers use specific tools to achieve a
planned result with an ideal outcome in mind
It is a tinkerer It does the best it can with what is
available Some evolutionary changes appear to be
constant, small-scale improvements (not long term “projects”)
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Results of Tinkering
Human females spontaneously abort nearly all malformed fetuses before the first 3 weeks of pregnancy
Humans have developed an association between pleasure and sex to spur them to reproduce
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Tinkering and the Human Brain
New structures superimposed over old ones
Conflicts between the “visceral” brain and the logical brain occur because of these additional structures and connections
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Conclusions
Darwin, Wallace, and many others represent the foundation of the unifying theory of evolution
Theories about evolution are shifting because of new genetic information and breakthroughs in other fields
Though most scientists agree evolution is a fact, there are still questions about types of evolution (sympatric vs. allopatric), its speed, and how exactly it occurs
Developing fields like genetics and evo devo are uncovering new information and raising even more questions