Download Introduction to Evolution

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Introduction to Evolution
One of the main theories
Many contributors
Many sources of information
Controversial in U. S.
School boards fight over inclusion
Surveys of high school biology teachers: approximately 38% hesitate teaching evolution
Evolution and its Core Principles
 No other concept in biology has the explanatory power of evolution
 No other factor has so strongly shaped life
 Evolution is the mortar holding all of the various fields of biology together
Evolution and its Core Principles
 The evidence for evolution was amassed in the same way that scientific evidence is gathered
in any field
 Rigorous measurement
 Conducting experiments, etc.
Evolution and its Core Principles
 The theory of evolution is very far-reaching
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 Important beyond the domain of biology
 Alters basic assumptions about the world
Evolution and its Core Principles
Humans can no longer view themselves as something separate from all other living things
 Humans, and all other living things, are descended from other species
 We are one tiny branch of an immense evolutionary tree
Evolution and its Core Principles
Most fields of scientific research tell us about small-scale processes in the living world
Evolutionary biology tells us about the origins and development of the living world
 Evolution carries considerable philosophical and even religious meaning
Evolution and its Core Principles
 The theory of evolution is very far-reaching
 Important beyond the domain of biology
 Alters basic assumptions about the world
Evolution and its Core Principles
 It is the Theory of Evolution that allows us to make sense of the diversity of nature
 Two principles lie at the core of this theory
 Common descent with modification
 Natural selection
Evolution and its Core Principles
Common descent with modification
 Groups of living things can undergo modification in successive generations
 Such change can result in the formation of new and separate species
Common Descent
 All of the branches in the evolutionary tree of life can be traced back to a single trunk
 All living things on Earth are ultimately descended from a single, ancient ancestor
Evolution and its Core Principles
Natural selection
 Differential adaptation of organisms to the environment selects those traits that will be passed
on with greater frequency from one generation to the next
 Natural selection is the most important process shaping evolution
Evolution and its Core Principles
 Evolution provides us a means of understanding nature in all its complexity
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 Allows understanding of familiar things
 Answers the “why” questions
 Allows an understanding of new natural phenomena
 Appearance of antibiotic-resistant bacterial strains (simply an evolutionary adaptation
in rapidly evolving bacteria)
Evolution and its Core Principles
Humans can no longer view themselves as something separate from all other living things
 Humans, and all other living things, are descended from other species
 We are one tiny branch of an immense evolutionary tree
Evolution and its Core Principles
Understanding evolution meant the end of the idea of a fixed living world
 Life forms only appear to be fixed because the human lifespan is so short relative to
evolutionary time
 Birds have not always been birds
 Descendants of dinosaurs
 Whales have not always been whales
 Descendants of land-walking mammals
 etc.
Evolution and its Core Principles
Life has been shaped through natural selection
 Natural selection shapes, but it does not design
 No mind and no goals
 No consciousness and no morals
 Neither cruel nor kind, simply indifferent
Charles Darwin and the Theory of Evolution
The essentials of the theory of evolution were assembled by Charles Darwin
 Nineteenth-century British naturalist
 Left medical school
 Attended Cambridge as divinity student
Darwin and the Theory of Evolution
 Darwin’s contributions were twofold
 Developed existing ideas about descent with modification
 Provided a large body of evidence in support of descent with modification
 First to perceive that natural selection is the primary mechanism of evolutionary change
Darwin and the Theory of Evolution
 Darwin became the resident naturalist upon the HMS Beagle
 22 years old
 Position arranged by one of his Cambridge professors
 Ship was to survey coastal areas
 Particularly the South American coast
 Darwin spent the next five years on this research vessel
Darwin’s Voyage
 Needed to ask permission; objections included
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Disreputable
Wild scheme
Second choice
Something wrong with vessel
Never settle down
Uncomfortable accommodations
Change professions again
Useless endeavor
Darwin’s Voyage
Pickling jars
Notebooks
Packing materials
Few articles of clothing
Two books
 Bible
 Principals of Geology by Charles Lyell
Evolutionary Thinking
before Darwin
Charles Lyell’s Principles of Geology
 Published in 1830
 Geological forces still operating could account for the changes geologists could see in the
Earth’s surface
 Earth had not been put in its final form at its moment of “creation”
 The Earth must be much older than originally thought
Evolutionary Thinking before Darwin
Darwin’s realization during and after voyage
 If slow and continual change is sufficient to bring about drastic change on the Earth itself,
then perhaps such slow and continual change is also sufficient to bring about drastic
change amongst the living world
Evolutionary Thinking before Darwin
Jean-Baptiste de Lamarck (1809)
 Acquired characteristics: argued that ducks gained webbing on their feet through
swimming, passed this trait on to offspring
 He correctly understood that populations do evolve
 The mechanism Lamarck proposed for this evolutionary change was not accurate
Evolutionary Thinking before Darwin
Georges Cuvier examined fossil-laden rocks of the Paris Basin
Provided conclusive evidence of the extinction of species on Earth
 Radical notion
 Many Christians believed that their creator would never allow one of his creatures to perish
 Cuvier erroneously thought that new acts of creation followed acts of devastation
Darwin’s Insights Following
the Beagle’s Voyage
Darwin observed and collected specimens throughout his entire voyage
Four years into the voyage, the Beagle spent five weeks at the Galápagos Islands
 Volcanic outcroppings west of Ecuador
Darwin saw many strange animals
 Iguanas, tortoises, birds, etc.
 These animals varied between the islands
Darwin’s Insights
 A bird expert at the Zoological Society of London identified the birds Darwin collected in the
Galápagos Islands
 The three varieties of mockingbirds represented three different species
 The small birds were all separate species of finches
 Species found nowhere but the Galápagos
 Darwin had believed them to be blackbirds, finches, wrens, and warblers
Darwin’s Insights
 In these finches, Darwin saw common descent
The Galápagos finches were related to finches on the South American mainland
Mainland finches were transported to the Galápagos Islands
Over time, these finches diverged into separate species
Galápagos tortoises, iguanas, and cactus plants displayed the same pattern
Darwin’s Insights
In these finches, Darwin saw common descent
 The Galápagos finches were related to finches on the South American mainland
 Mainland finches were transported to the Galápagos Islands
 Over time, these finches diverged into separate species
 Galápagos tortoises, iguanas, and cactus plants displayed the same pattern
Post-Beagle Darwin
Mental rioting: tried to make sense of what he observed
Cautious: returned a celebrity, hesitant to publish his ideas and conclusions
Wrote: coral reef formation, natural history notes
Lots of breeding experiments
Post-Beagle
Artificial selection
Lots of variability by selective breeding
Pigeons
 Start with plain old pigeon
 End with fancy pigeons
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Darwin’s Insights
 Read article by T. Malthus, as recreational reading
 An Essay on the Principle of Population by T. R. Malthus
 Malthus discussed human populations competing for limited resources
 Darwin realized that competition for limited resources was common feature of all
populations
 Darwin saw this “struggle for existence” as a key driving force of evolution
Darwin’s Insights
 Organisms having “favorable variations” were preserved
 Left proportionally more offspring
 Organisms having “unfavorable variations” were destroyed
 Left fewer or no offspring
Darwin’s Insights
 Over generations, organisms evolved in the direction of the favorable variations
 Malthus solidified natural selection concept
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Extensive study and writing
Reflection on what he had seen
Secret notebooks
Tree of life developed
Darwin’s Insight
 Alfred Russel Wallace
Alfred Russel Wallace
English naturalist
Collected bird and butterfly specimens from South America and Southeast Asia
Independently realized that natural selection is the mechanism of evolution
Recorded his ideas and sent them, ironically, to Charles Darwin
Alfred Russel Wallace
Wallace’s manuscript and some of Darwin’s letters were both presented at a meeting of a
scientific society in 1858
 Darwin completed his work and published it the following year
 The entire first printing of this book sold out on the first day it was published
Alfred Russel Wallace
Darwin and Wallace independently determined that natural selection was the driving force
behind evolution
 Darwin formulated the theory decades before Wallace
 Darwin supported his ideas with far more documentation than Wallace
 Darwin received the bulk of the credit for elucidating the mechanism of evolution
On the Origin of Species
1859
Sold out first printing in a few days
Over 600 pages
One illustration: The Tree of Life
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The Acceptance of Evolution
 Darwin’s ideas sparked both praise and scorn
 Within fifteen years of publishing The Origin, virtually all naturalists accepted that evolution
occurred
 Scientists had little trouble accepting the fact of evolution
The Acceptance of Evolution
 It took scientists longer to accept that natural selection was the means by which evolutionary
change occurs
 This wasn’t universally accepted until the middle of the 20th century
 The theory part of evolutionary change
The Acceptance of Evolution
 It took scientists longer to accept that natural selection was the means by which evolutionary
change occurs
 This wasn’t universally accepted until the middle of the 20th century
 The theory part of evolutionary change
Opposition to The Theory of Evolution
 Evolution has an unusual status among major fields of biology
 Its findings are regularly being challenged as being unproven or simply wrong
 For the average person, these attacks make it appear that the theory of evolution is just a
guess, rather than being solidly grounded in evidence
Opposition to Evolution
 There is no legitimate “scientific debate” regarding the occurrence of evolution
 Why do many people have the mistaken impression that there is such a debate?
 There is widespread misunderstanding of the word “theory”
 The nature of the historical evidence for evolution is widely misunderstood
Opposition to Evolution
Is evolution “just a theory?”
 Term “theory” has two vastly different meanings
 In everyday speech, a theory is often little more than a hunch, often without evidence
 A scientific theory is a related set of insights supported by evidence
 Able to explain some aspect of nature and possessing explanatory power
What is a theory?
 Examples
 Cell Theory
 The Theory of Gravity
 The Big Bang Theory
 Einstein’s Theory of Relativity
 Darwin’s Theory of Evolution
Opposition to Evolution
Opposition to Evolution
What is a theory?
 These theories have survived, and continue to withstand, the questioning of critics
 Legitimate scientific debate does not argue that gravity, evolution, or cells do not exist
 Legitimate scientific debate centers only on minor aspects of these theories
Opposition to Evolution
Can we even see that evolution happens?
 Evolution can not be observed as directly as one can observe cells
 The evidence for evolution is more historical than is the evidence for genetics or
photosynthesis
 Still, this evidence is compelling
Opposition to Evolution
Can we even see that evolution happens?
 Arguing that one cannot see evolution is like arguing that we cannot see the ancient Roman
Empire
 In both cases, there is a record of their existence
Opposition to Evolution
Can we even see that evolution happens?
 Any ancient historical record, including the fossil record, is fragmentary
 An incomplete record leaves room for a great deal of interpretation among scientists…
Opposition to Evolution
Can we even see that evolution happens?
 This interpretation has to do with the details of evolution, not with its core principles
 e.g., Which group descended from which group, the rate of evolution, etc.
 It does not have to do with whether evolution occurred
The Evidence for Evolution
 What makes scientists so sure about the core principles of evolution?
 Lines of evidence are internally consistent
 Lines of evidence are consistent with other lines of evidence
The Evidence for Evolution
 Any glaring inconsistency within or between lines of evidence would call evolutionary theory
into question
 No such inconsistencies have surfaced in the 150 years since Darwin
 Multiple lines of evidence demonstrate descent with modification
The Evidence for Evolution
 Billions of years have elapsed since the first appearance of life
 Radiometric dating can determine the age of objects
 Measures the rate of decay of radioactive elements (isotopes)
 Decay occurs at a constant rate
 An isotopes “half-life” is the amount of time it takes for half of a given amount to
decay into a more stable form
The Evidence for Evolution
 An isotopes “half-life” does not change
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 e.g., The half-life of carbon-14 is always approximately 5,000 years
 e.g., The half-life of uranium-238 is always approximately 4.5 billion years
One can accurately determine the age of a rock by comparing the proportions of radioactive
and non-radioactive isotopes
The Evidence for Evolution
Fossils provide powerful evidence for evolutionary change
 Similar fossils are found in rocks of similar ages throughout the world
 A general movement toward increasing complexity is noted as one views newer and newer
layers of rock
The Evidence for Evolution
Scientific claims must be falsifiable
 The fossil record presents a falsifiable claim
 e.g., Trilobites existed in ancient oceans from 500 million until 245 million years ago
 e.g. Primates arose 80 million years ago
 Humans are an example of a modern primate
The Evidence for Evolution
Scientific claims must be falsifiable
 If a fossil bed containing both trilobites and humans was found, our ideas of evolutionary
sequences would be called into question
 No such incompatible pairing has been found
The Evidence for Evolution
 The line of fossil evidence is internally consistent
 When fossil placement is compared to dates obtained by radiometric dating, we get excellent
agreement between these two lines of evidence
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The Evidence for Evolution
Morphology is the study of physical forms that organisms take
Comparative morphology provides classic evidence for evolutionary change
 e.g., A very diverse group of mammals display striking similarities in their forelimb
structure
 One upper bone, two intermediate bones, and five digits
The Evidence for Evolution
 These forelimbs are similar due to shared evolutionary ancestry, not because this similarity is
necessary for function
 “Homologous structures”
 All mammals evolved from a common ancestor
 This common ancestor possessed this 1-2-5 structure
 Adaptations to different environments modified this structure in different ways
The Evidence for Evolution
 Many organisms possess fairly useless structures
 e.g., Human auricular muscles
 Allow us to wiggle our ears
 Placement of these costly and useless structures seems strange if we considered living
things to be intelligently designed
 How do we explain such structured from an evolutionary perspective?
The Evidence for Evolution
 Our auricular muscles are homologous to those of a cat
 These muscles are not functional in humans
 These muscles are functional in a cat (etc.)
The Evidence for Evolution
 These organs were presumably functional in a common ancestor to both humans and cats
(and many other mammals)
 Their function has been lost during the course of evolution
 “Vestigial characters”
The Evidence for Evolution
 Why would a flightless bird such as the ostrich possess wings?
 Wings do help to balance ostriches, but why would a designer fashion wings simply for
balance, when they have such a different function in other birds?
 The ostrich descended from birds that could fly, but its own line evolved into a flightless
condition
The Evidence for Evolution
 Comparative morphology is also evident in embryonic development
 “Comparative embryology”
 e.g., Fish, chickens, humans, etc. possess pharyngeal slits during their development
 Develop into gills in fish
 Develop into eustacian tubes in humans
 Similarities in embryonic development are due to descent from a common ancestor
The Evidence for Evolution
 Every living thing on Earth has DNA as its genetic material
 The genetic code is identical in virtually all living things
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 Triplet of DNA bases  specific amino acid
 The very few differences are minor
If all life on Earth descended from a common ancestor, one would expect this type of
similarity in the genetic code
The Evidence for Evolution
Common ancestors possessed numerous genes
 Many of these genes should be present in species descending from this common ancestor
 These genes should have similar, but not identical DNA sequences in these descendant
species
 Mutations would alter this DNA sequence at a fairly constant (and very slow) rate
The Evidence for Evolution
Evolutionary theory predicts that the number of DNA base-pair differences between two
species should reflect the evolutionary distance between these two species
 e.g., There should be relatively many differences between a human and a yeast
 e.g., There should be relatively few differences between a human and a pig
The Evidence for Evolution
Mutations are like a “molecular clock”
 Able to measure the evolutionary distance between species
The Evidence for Evolution
These predictions have been borne out by the sequencing of the cytochrome c oxidase gene
 Similar results have been found with numerous other genes as well
The Evidence for Evolution
 Molecular data provides additional confirmation for evolution between lines of evidence
 Consistent with radiometric dating
 Consistent with the fossil record
 Consistent with comparative anatomy
Evolution Cartoons
 The Far Side: too numerous to count
 Human and Macague Genome
Evolution Videos
How Evolution Works
 Common Descent
 Natural Selection
 Components
 Raw material: variation
 Selection
 Time