chapter 22: evolution

.

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

http://www.auburn.edu/academic/classes/biol/1020/bowling/

.

• 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.


.

Historical perspective

divine design and perfection model

fossils

acquired traits

modern geology – Lyell, uniformitarianism, and the ancient Earth

artificial selection

population limits


.


.

Historical perspective divine design and perfection model

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

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

all organisms were seen as moving toward perfection

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

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


.


fossils fossils were known for centuries before Darwin

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)


.

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).


.

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, andI 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Darwin: A Record of His Work in a Series of Hitherto Unpublished Letters edited byF. Darwin and A. Seward (D. Appleton and Co., New York, 1903).


.

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.


.

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 VariousCountries Visited by H.M.S. Beagle by Charles Darwin (facsimile edition of 1839

First Edition, Hafner Publishing Company, New York, 1952).


.

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


.

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


.

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


.

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)


.

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


.

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


.

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).


.

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.

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 voyage1831: 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


.

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)


.

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


.


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


.


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

mathematically, populations will grow geometrically if unchecked

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

population limits that would allow selection to act naturally were recognized


.


artificial selection it was well known that domesticated animals and plants had been breed

over centuries by humans to produce different varieties

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


.

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


.

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!


.

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, whileAlfred Russel Wallace ventured far up the Rio Negro. Bates found more than

550 species of butterflies at Ega (now Tefé). Drawn by Leanne Olds.


.

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. Itdisplays 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).


.

Figure 2.2 The Malay Archipelago.Map by Leanne Olds.


.

Figure 2.3 The Golden Birdwing butterfly.Wallace discovered this form (Ornithoptera

croesus lydius) on the island of Batjan.Photograph by Barbara Strnadova.


.

Figure 2.4 The Wallace Line.


.

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.


.



Darwin’s voyage






.

• Describe the logical reasoning behind Darwin’s concept of 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


.


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.


.


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

http://evolution.berkeley.edu


http://evolution.berkeley.edu/

.

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


.



Darwin’s voyage






.

• Discuss these major lines of evidence for evolution: – fossil record– anatomical evidence (comparisons, vestigial

structures, “design” flaws)– distribution of organisms– developmental comparisons– molecular comparisons


.

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, whileAlfred Russel Wallace ventured far up the Rio Negro. Bates found more than

550 species of butterflies at Ega (now Tefé). Drawn by Leanne Olds.


.

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 aremimics 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 membersof 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 thatmimic Leptalis amphione and Leptalis orise.


.

Figure 3.3 Caterpillar mimic of snake head.First discovered by Bates, a number of species mimic the appearance of

snakeheads. This is the Spicebush Swallowtail caterpillar (Papilio trollus).

Photo by Mary Jo Fackler.


.

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

Photos by Gary Nafis.


.


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

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


.

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

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


.


Basilosaurus, a fossil whale


http://www.auburn.edu/academic/classes/biol/1020/bowling/evolution.htm

http://www.auburn.edu/academic/classes/biol/1020/bowling/evolution.htm

.



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



http://www.sciencemag.org/cgi/content/summary/307/5716/1728

.

Evidence supporting the theory of evolution the fossil record

fossils most commonly form in sedimentary rocks in aquatic environments

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

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


.

• Explain how fossils are dated.


.

dating fossils

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

Youngest


.

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


.

dating fossils

radiometric dating 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

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

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


http://id-archserve.ucsb.edu/Anth3/Courseware/Chronology/09_Potassium_Argon_Dating.html#KARDecay

.

dating fossils

radiometric dating another example:

carbon-14 decaying to nitrogen-14 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


http://id-archserve.ucsb.edu/Anth3/Courseware/Chronology/08_Radiocarbon_Dating.html

.

• Explain how fossils are dated.


.


organs or structures that have similar form due to a common evolutionary origin are called homologous features

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

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


.


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

natural selection will logically lead to degeneration of unused features

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


.


not all organs or structures with functional similarity have a common origin

such cases are called homoplastic features, or analogous features

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

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


.

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)


.

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.


.

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


.

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


.

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

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

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

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


.


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

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

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



.



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)

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


.

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.


.

http://www.pnas.org/content/88/20/9051.full.pdf+html

http://www.youtube.com/watch?v=8FGYzZOZxMw

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






.

• 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


.



Darwin’s voyage






.

• 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


.


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


.


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”?


.



Darwin’s voyage






.


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.”


.


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


chapter 22: evolution

Documents