Chapter 22: Evolution 

Historical perspective on evolution



Darwin’s voyage



Darwin’s theory: evolution occurs by natural selection



Evidence supporting the theory of evolution



The Modern Synthesis



The central role of evolution in modern biology .

Chapter 22: Evolution 

Historical perspective on evolution



Darwin’s voyage



Darwin’s theory: evolution occurs by natural selection



Evidence supporting the theory of evolution



The Modern Synthesis



The central role of evolution in modern biology .

•

Describe the major ideas on evolution and related topics that had a significant influence on Charles Darwin as he developed the concept of evolution by natural selection.

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Historical perspective 

divine design and perfection model

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fossils

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acquired traits

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modern geology – Lyell, uniformitarianism, and the ancient Earth



artificial selection



population limits .

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Historical perspective divine design and perfection model

 

from Aristotle, whose ideas dominated most thinking on biology until the renaissance

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species were viewed on a scale from simple to complex (which was considered more perfect)

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all organisms were seen as moving toward perfection



based on divine intervention and design (thus supernatural, outside the true realm of science)

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now discredited in biology, but still part of the social consciousness

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Historical perspective fossils

 

fossils were known for centuries before Darwin

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fossils reveal organisms unlike any living today



the idea that some fossils represent species that had become extinct was recognized even as early as Leonardo da Vinci (1452-1519)

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Figure 1.4 A mylodon. Drawing of a giant ground sloth. From A Naturalist’s Voyage Around the World: The Voyage of the H.M.S. Beagle by Charles Darwin (D. Appleton and Co., New York, 1890).

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Figure 1.1 “I was in many ways a naughty boy.” Portrait of young Charles and his sister Catherine. Charles later wrote in his autobiography, “I was much slower in learning than my younger sister Catherine, and I believe that I was in many ways a naughty boy.” From More Letters of Charles Darwin: A Record of His Work in a Series of Hitherto Unpublished Letters edited by F. Darwin and A. Seward (D. Appleton and Co., New York, 1903).

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Figure 1.2 Charles’ list of his father’s objections to the Beagle voyage. Reproduced by kind permission of the Syndics of Cambridge University Library.

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Figure 1.3 The HMS Beagle and Darwin’s quarters. Based on a drawing by shipmate Philip King, with whom Darwin shared his quarters. From Journal of Researches into Geology and Natural History of the Various Countries Visited by H.M.S. Beagle by Charles Darwin (facsimile edition of 1839 First Edition, Hafner Publishing Company, New York, 1952).

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Figure 1.6 HMS Beagle in the Strait of Magellan. Drawing from A Naturalist’s Voyage Around the World: The Voyage of the H.M.S. Beagle by Charles Darwin (D. Appleton and Co., New York, 1890).

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Figure 1.7 Map of the Voyage of the HMS Beagle, 1831–1836. Drawn by Leanne Olds.

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Historical perspective birth of modern geology – Lyell, uniformitarianism, and the ancient Earth





prior to the early 1800s, the world view of most was that the Earth is very young (around 6000 years old)



in the early 1800s, geologists began to apply scientific reasoning to studies of geological processes, and quickly recognized that these processes require that the Earth be very old (billions of years) to occur naturally

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Historical perspective 

this “uniformitarian” model of geological processes was made famous by Lyell’s Principles of Geology, which influenced Charles Darwin



the uniformitarian model is essentially the basis of geology today; confirming tests of this model include dating rocks using radioisotope ratios (more on that later)

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Figure 1.7 Map of the Voyage of the HMS Beagle, 1831–1836. Drawn by Leanne Olds.

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Figure 1.9 Galapagos finches. Drawing from A Naturalist’s Voyage Around the World: The Voyage of the H.M.S. Beagle by Charles Darwin (D. Appleton and Co., New York, 1890).

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Figure 1.8 A Galapagos tortoise. Drawing from A Naturalist’s Voyage Around the World: The Voyage of the H.M.S. Beagle by Charles Darwin (D. Appleton and Co., New York, 1890).

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1831:

Leaves on Beagle (age 22)

1836:

Beagle returns to England; soon afterwards writes his story of the trip and begins his “secret notebooks”

Darwin’s voyage

Figure 1.7 Map of the Voyage of the HMS Beagle, 1831–1836. Drawn by Leanne Olds.

Figure 1.10 The tree of life. Page from notebook “B,” where Darwin recorded his idea that life is connected like the branches of a tree, with ancestors at the bottom. Reproduced by kind permission of the Syndics of Cambridge University Library.

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Darwin’s voyage 1831:

Leaves on Beagle (age 22)

1836:

Beagle returns to England; soon afterwards writes his story of the trip and begins his “secret notebooks”

1838:

Reads Malthus’ Essay on the Principle of Populations

1839:

Voyage of the Beagle published

1842:

Makes 35-page sketch of theory

1844:

Expands sketch to 230 pages

1859:

Publishes On the Origin of Species by Means of Natural Selection

1871:

Publishes The Descent of Man and Selection in Relation to Sex

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Darwin’s voyage There was much discussion by immediate predecessors and contemporaries of Darwin about:





how the divine design model did not mesh well with observation of the extremes of variation among species



the idea of extinct species represented in the fossil record



functional similarities between the anatomy of extremely divergent species



the idea that evolution occurs thus was “in the air” at the time



attempts to find a convincing mechanism fell short (such as Lamarck’s acquired characteristics model)

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Historical perspective acquired traits

 

mostly associated with Lamarck (1744-1829)



still focused on a model of organisms driven toward complexity, but involved an explanation with natural causes



postulated that changes or “acquired characteristics” during an organism’s life could be passed on to offspring



famous example was Lamarck’s model for how giraffes developed long necks – he claimed that stretching of the neck in one generation would lead to offspring with longer necks



understanding of genetic inheritance has led to rejection of acquired traits models

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Darwin’s theory: evolution occurs by natural selection Darwin’s theory of evolution was based on four general observations:







overproduction



variation



competition



differential reproductive success natural selection will produce a population of individuals more suited to their environment through time

.

Historical perspective population limits that would allow selection to act naturally were recognized





Malthus (1766-1834) wrote the most influential works on this subject



mathematically, populations will grow geometrically if unchecked

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food supplies rarely can be expected to grow faster than arithmetically, thus putting a limit on population growth

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Historical perspective artificial selection



it was well known that domesticated animals and plants had been breed over centuries by humans to produce different varieties

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indicates that the characteristics of a species can be modified by selection

some examples:

 

different breeds of dogs



“wild cabbage” lineage of cabbage, broccoli, cauliflower, Brussels sprouts, collards, kale, etc.



many more

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Figure 1.9 Galapagos finches. Drawing from A Naturalist’s Voyage Around the World: The Voyage of the H.M.S. Beagle by Charles Darwin (D. Appleton and Co., New York, 1890).

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Darwin’s voyage Recall Darwin’s theological training –

 

Darwin was well aware of the impact that a workable, testable theory of evolution would have



…and the intense controversy and scrutiny it would draw…



so, although he worked out most of his theory of evolution shortly after his trip on the Beagle



…he spent 20 years accumulating evidence and doing experiments before finally publishing the idea!

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Darwin’s voyage 

Darwin was spurred on to publish when Alfred Russel Wallace shared his independent work where he had reached similar conclusions to Darwin



they first presented the theory of evolution by natural selection together in 1858 .

Figure 3.1. The massive Amazon River system. The main river and its tributaries span more than fifteen thousand miles. Henry Walter Bates spent most of his eleven years in the Amazon on the main river, while Alfred Russel Wallace ventured far up the Rio Negro. Bates found more than 550 species of butterflies at Ega (now Tefé). Drawn by Leanne Olds.

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Figure 2.1 Sketch salvaged from fire and shipwreck of the Helen. This drawing of an Amazonian angelfish was one of the few sketches Wallace managed to save out of all of his notes and specimens on his doomed voyage home. It displays one of the important talents for naturalists before the age of photography — that of being a good artist. Drawing from the autobiography of Alfred Russel Wallace, My Life (New York: Dodd, Mead, and Co., 1905).

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Figure 2.2 The Malay Archipelago. Map by Leanne Olds.

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Figure 2.3 The Golden Birdwing butterfly. Wallace discovered this form (Ornithoptera croesus lydius) on the island of Batjan. Photograph by Barbara Strnadova.

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Figure 2.4 The Wallace Line.

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Darwin’s voyage 

Darwin published his first version of the book On the Origin of Species by Means of Natural Selection in 1859



in it, he laid out the entire argument with all of the evidence that he had been gathering ever since his voyage on the Beagle .

Darwin’s voyage Darwin’s book had immediate and dramatic impact





the force of his argument and evidence convinced many scientists quickly



of course it stirred tremendous controversy as well



Darwin made several revisions of his work in response to some of the most reasonable criticisms



He also focused on human evolution in The Descent of Man (1871)

.

•

Describe the major ideas on evolution and related topics that had a significant influence on Charles Darwin as he developed the concept of evolution by natural selection.

.

Chapter 22: Evolution 

Historical perspective on evolution



Darwin’s voyage



Darwin’s theory: evolution occurs by natural selection



Evidence supporting the theory of evolution



The Modern Synthesis



The central role of evolution in modern biology .

•

Describe the logical reasoning behind Darwin’s concept of natural selection.

.

Darwin’s theory: evolution occurs by natural selection Darwin’s theory of evolution was based on four general observations:







overproduction – each species produces more offspring than will survive to maturity



variation – individuals in a population vary, and some of the variation is heritable (this was expanded by others later, as genetics came to be understood)



competition – there is competition among the individuals of a population for limited resources (struggle for existence)



differential reproductive success – individuals that possess more favorable characteristics (in the pool of variation) are more likely to survive and reproduce; those with less favorable characteristics are less likely to survive and reproduce

thus, natural selection will produce a population of individuals more suited to their environment through time

.

Darwin’s theory: evolution occurs by natural selection 

when populations are separated (such as the geographic separation of islands from each other and a nearby continent), natural selection on two separate populations can produce two distinct populations with different characteristics – resulting in two separate species



note that for this theory to explain the current variety of species on Earth, there is a need for a long amount of time for natural selection to produce the variety observed; thus, the idea of an ancient Earth hundreds of millions to billions of years old is crucial .

•

Describe the logical reasoning behind Darwin’s concept of natural selection.

.

•

Explain the terms microevolution and macroevolution (in their true scientific meanings), and describe how microevolution can lead to macroevolution.

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Darwin’s theory: evolution occurs by natural selection 

two major branches: microevolution, or changes of a population over time, and macroevolution, or the formation of species



http://evolution.berkeley.edu .

•

Explain the terms microevolution and macroevolution (in their true scientific meanings), and describe how microevolution can lead to macroevolution.

.

Chapter 22: Evolution 

Historical perspective on evolution



Darwin’s voyage



Darwin’s theory: evolution occurs by natural selection



Evidence supporting the theory of evolution



The Modern Synthesis



The central role of evolution in modern biology .

• Discuss these major lines of evidence for evolution: – fossil record – anatomical evidence (comparisons, vestigial structures, “design” flaws) – distribution of organisms – developmental comparisons – molecular comparisons

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Figure 3.1. The massive Amazon River system. The main river and its tributaries span more than fifteen thousand miles. Henry Walter Bates spent most of his eleven years in the Amazon on the main river, while Alfred Russel Wallace ventured far up the Rio Negro. Bates found more than 550 species of butterflies at Ega (now Tefé). Drawn by Leanne Olds.

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Figure 3.2 Mimicry in butterflies. This is an original plate from Bates’ 1862 paper reporting the discovery of mimicry. The butterfly at the center (5) is Leptalis nehemia, the typical butterfly of the family. The other Leptalis butterflies (1–8) deviate greatly from this pattern, as they are mimics of other species. Each pair (3/3a, 4/4a, 6/6a, 7/7a, 8/8a) illustrates mimicry between Leptalis and species of other families. Specimens 3a, 4a, and 6a are members of the genus Ithomia that mimic varieties of Leptalis theonoe found in the area of Sao Paulo. Specimens 7a and 8a are members of the Mechanitis and Methona genera that mimic Leptalis amphione and Leptalis orise.

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Figure 3.3 Caterpillar mimic of snake head. First discovered by Bates, a number of species mimic the appearance of snake heads. This is the Spicebush Swallowtail caterpillar (Papilio trollus). Photo by Mary Jo Fackler.

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Figure 3.4 Mimicry in snakes. Arizona Mountain kingsnake (top) and Arizona coral snake (bottom). Photos by Gary Nafis.

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Evidence supporting the theory of evolution 

the fossil record



comparative anatomy of related species



distribution of plants and animals



related species have similar patterns of development



molecular comparisons among organisms .

Evidence supporting the theory of evolution the fossil record



fossils provide direct evidence for change over time

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fossils range from mineralized casts or imprints (most commonly of bone, teeth, and shells, but sometimes of softer tissues) to actual body parts preserved in bogs, tar, amber, or ice



fossils provide evidence of intermediates between extant and extinct forms

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Evidence supporting the theory of evolution fossils provide direct evidence for change over time





many relatively complete examples of transitions in body forms are known, such as the evolutionary lineage of horses and the transition of terrestrial species to modern whales

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the fossil record provides tests of evolution as an explanation for the history of life on Earth – fossils can be dated, and the age of fossils invariably matches the predicted place of those body forms in the history of life on Earth

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fossils provide direct evidence for change over time

Basilosaurus, a fossil whale

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fossils provide direct evidence for change over time

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fossils provide direct evidence for change over time

McFadden, Bruce. 2005. “Fossil Horses – Evidence of Evolution.” Science Vol. 307. no. 5716, pp. 1728 – 1730

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Evidence supporting the theory of evolution the fossil record



fossils most commonly form in sedimentary rocks in aquatic environments

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the fossil record is biased toward organisms with hard parts that lived in aquatic or arid environments, where decay is slow and incorporation in rocks can occur with reasonable speed

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organisms that lived in places of rapid decay are thus biased against in the fossil record

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•

Explain how fossils are dated.

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dating fossils

Youngest

relative position in rock layers





sedimentary layers most commonly have the youngest layers nearer the surface, and are progressively older as you go deeper



large-scale geological events can be used to correlate rock strata from different sites; other dating methods are also used to correlate rock strata

Oldest .

dating fossils 

association with index fossils that have been dated by other means from other locations



radiometric dating 

each radioisotope has characteristic, constant rates of decay



some allow for measurement of when a rock was formed or when an organism died

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dating fossils radiometric dating

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example: potassium-40 decaying to argon-40

 

when magma cools to solid rock, no argon is in the rock (escapes as the rock forms)



once the rock hardens, the radioactive clock begins – potassium-40 in the rock decays to argon-40

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measurement of the amounts of potassium-40 and argon-40 in the rock today are used to determine an age range for when the rock could have been formed

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half-life of 1.3 billion years: used for fossils tens of millions to billions of years old

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dating fossils radiometric dating

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another example: carbon-14 decaying to nitrogen-14

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

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half-life of 5730 years



used for organic remains hundreds to tens of thousands of years old

there are hundreds of well-studied sites with fossils that have been dated in some way; no truly incongruous fossils have been found

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•

Explain how fossils are dated.

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comparative anatomy of related species organs or structures that have similar form due to a common evolutionary origin are called homologous features

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

example: the similarity between the human arm, the dolphin's flipper, the bat's wing, and the bird's wing

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example: plant leaves, cactus needles, flower sepals and petals

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comparative anatomy of related species vestigial structures – a feature that once had a role in the evolutionary history of a species but that no longer functions

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natural selection will logically lead to degeneration of unused features

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however, it is not easy to completely remove by natural selection – thus, vestiges are left behind

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comparative anatomy of related species not all organs or structures with functional similarity have a common origin

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

such cases are called homoplastic features, or analogous features

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resemblance between homoplastic features is superficial – consider an insect's wing and a bird's wing

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independent evolution of similar features in distantly related organisms is called convergent evolution

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distribution of plants and animals 

biogeography – the study of the past and present geographical distribution of organisms



organisms on islands are most closely related (in form and genetically) to those from the nearest mainland, not those from similar islands in different parts of the world .

distribution of plants and animals biogeography – the modern theory of plate tectonics and reconstruction of the history of land masses on Earth explains:





much of the observed fossil distributions



timings of geographic isolations that would be expected for some modern distributions of species (example: the dominance of marsupials in Australia)

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Figure 2.4 The Wallace Line. Wallace discovered that the narrow strait between Bali and Lombok marked a boundary between Asiatic fauna (with tigers, rhinoceri, and orangutans) and Australia-type fauna (with kangaroos, cuscus, and other marsupials). Bali was once connected to the Asiatic continental shelf, but not to Lombok. The boundary line extends throughout the archipelago as shown. Drawn by Leanne Olds.

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related species have similar patterns of development 

very young embryos of reptiles, birds, mammals, and humans are indistinguishable



studies of developmental biology are revealing the common genetic basis for such similarities – “devo/evo” study is one of the hottest fields in biology today

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• Discuss how DNA sequence comparisons and “molecular clocks” work.

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molecular comparisons between organisms the “big test” for the theory of evolution by natural selection was this:





evolution by natural selection on inherited traits predicts that genetic sequence information will provide a record of evolutionary change and evolutionary relationships

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these genetic records should correlate with evolutionary relationships that have been established by other means, such as biogeography and comparative anatomy .

molecular comparisons between organisms evolution has passed this test with flying colors

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the virtual universality of the genetic code is compelling evidence of a common ancestor

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changes in proteins and nucleic acids provide a record of evolutionary change

detailed molecular studies have clearly documented microevolution in many cases, such as the emergence of antibiotic-resistant bacteria

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molecular comparisons between organisms changes in proteins and nucleic acids provide a record of evolutionary change

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DNA sequencing provides a means to measure genetic similarities and differences between species

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sequences of amino acids in proteins can also be used – these provide an indirect comparison of DNA sequences

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DNA and protein sequencing can be used to create a phylogenetic tree, a diagram showing the relatedness between species and lines of descent

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molecular comparisons between organisms changes in proteins and nucleic acids provide a record of evolutionary change

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DNA sequencing can also be used in some cases as a molecular clock to make some inference about when any two species diverged from each other (last shared a common ancestor)

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example – humans and chimpanzees: ~98% sequence identity, diverged about 6 million years ago

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Base Sequence Comparisons 

Divergence (difference) in nucleotide base sequence allows us to draw relationships between different organisms.



Here, differences in nucleotide base sequence of humans and some other primates compared.



Of the organisms with data given here, chimp DNA is the most like human DNA, and spider monkeys DNA is the least like human DNA.

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http://www.pnas.org/content/88/20/9 051.full.pdf+html http://www.youtube.com/watch?v=8 FGYzZOZxMw

Human Chromosome 2 and its analogs in the apes from Yunis, J. J., Prakash, O., The origin of man: a chromosomal pictorial legacy. Science, Vol 215, 19 March 1982, pp. 1525 - 1530

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• Discuss how DNA sequence comparisons and “molecular clocks” work.

.

• Discuss these major lines of evidence for evolution: – fossil record – anatomical evidence (comparisons, vestigial structures, “design” flaws) – distribution of organisms – developmental comparisons – molecular comparisons

.

Chapter 22: Evolution 

Historical perspective on evolution



Darwin’s voyage



Darwin’s theory: evolution occurs by natural selection



Evidence supporting the theory of evolution



The Modern Synthesis



The central role of evolution in modern biology .

•

What is the “modern synthesis”?

.

The modern synthesis of evolutionary theory combines Darwin’s concept of natural selection with genetics 

although Mendel was a contemporary of Darwin, remember that his work was largely unrecognized until around 1900



how traits are inherited was central to Darwin’s theory of evolution 

thus Darwin (and others) were keenly interested in finding working models of inheritance

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The modern synthesis of evolutionary theory combines Darwin’s concept of natural selection with genetics when genetic mechanisms came to be widely understood, they were quickly combined with Darwin’s model in the modern synthesis, also called Neo-Darwinism or the synthetic theory of evolution





this model emphasizes the genetics of populations



evolution is seen as working by natural selection on individuals to change the genetic makeup of populations over successive generations

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The modern synthesis of evolutionary theory combines Darwin’s concept of natural selection with genetics mutations play a key role in providing a source of genetic variation





without genetic variation, evolution cannot occur



mutations are necessary to produce genetic variation



while many mutations have no impact and many others are harmful, it is critical to recognize that some mutations are advantageous

.

•

What is the “modern synthesis”?

.

Chapter 22: Evolution 

Historical perspective on evolution



Darwin’s voyage



Darwin’s theory: evolution occurs by natural selection



Evidence supporting the theory of evolution



The Modern Synthesis



The central role of evolution in modern biology .

The central role of evolution in modern biology the modern synthetic theory of evolution is accepted today by most biologists as:







a robust and well-supported model



the central framework for the study of life

nearly all biologists today agree with the famous statement by the evolutionary geneticist T. Dobzhansky:

“Nothing in biology makes sense except in the light of evolution.”

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The central role of evolution in modern biology studies of evolution itself today focus largely on:



the causal processes of evolution, such as:

 

the speed of evolutionary change



the role of chance in evolution

molecular comparisons between and within species by

 

comparing DNA sequences



comparing genomes



comparing proteins and proteomes

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