1. Evolution

2. Evolution as Theory and Fact
Confusion sometimes arises as to
whether Evolution is a theory or a fact.
Actually it is both!
The theory of Evolution deals with how
Evolution happens. Our understanding
of this process is always changing.
Evolution is also a fact as there is a
huge amount of indisputable evidence
for its occurrence.
Presenter notes: There is often considerable confusion as to whether the concept of evolution is a theory or a fact. Actually it is both! Evolutionary theory deals with how evolution happens. This is an area of active research and new insights are constantly emerging to explain how one species gives rise to another. However, Evolution is also a fact because there is a great deal of indisputable evidence, as we will see in this talk, in support of its occurrence. What is uncertain is exactly HOW it happens, NOT whether it has happened at all.
Further background reading: Stephen Jay Gould, "Evolution as Fact and Theory," Discover 2 (May 1981): 34-37; available here:
Rodin’s “The Thinker” 2

3. LAMARCK
The lowest forms of life, such as bacteria, formed by spontaneous generation from lifeless matter, and each species would slowly change (i.e., evolve) into the next higher species on the scale
Use-Disuse model-if an organism used a body part it grew, if it didn’t, then it fell off
Whenever ADAPTATION was discovered, Lamarck attributed it to the effects of use and disuse under each individual's voluntary control

4. DARWIN'S IDEAS
Darwin's ideas were formulated principally during the voyage of H.M.S. Beagle.
Darwin saw many tropical habitats much richer in species than those he knew.
He noticed that the same habitat often produced different species on different continents: the savannahs (grasslands) of East Africa and the pampas (grasslands) of Argentina have almost no species in common.

5. Darwin traveled around the world in H.M.S. Beagle
Animals and Plants of South America are vastly different from those found in Africa or Australia

6. South American Mammals-these species are very different from the mammals found on other continents, even where climates are similar

7. Darwin noticed that islands (like the Galapagos) always had inhabitants whose nearest relatives were on the nearest continent
For example, the Galapagos Islands had birds and plants related to those of South America, while the Cape Verde Islands (volcanic, geologically similar to the Galapagos) had species related to those of Africa and unlike those of the Galapagos

8. Population-all the individuals of a species that live together in one place at one time

9. Galapagos Islands
Darwin’s Finches – land birds

10. Look at these pictures

11. First a few definitions
Adaptation-changing of a species that results in its being better suited to its environment

12. DARWIN”S FINCHES FROM THE GALAPAGOS ISLAND

13. DARWIN”S FINCHES FROM THE GALAPAGOS ISLAND

14. BRANCHING DESCENT WITH MODIFICATION
Darwin's was not the first evolutionary theory, but it was the first that emphasized BRANCHING descent (in treelike patterns), which Darwin called "descent with modification".
Descent with modification explained why classifications should have "groups within groups": families of related species, orders and classes made of related families, etc.

15. THE PATTERN OF BRANCHING DESCENT

16. Methods for Species
Isolation-when two populations of the same species cannot breed with one another
Extinct-when species disappear from the planet forever

17. Charles Darwin ( )
Origin Of Species by Means of Natural Selection
2 major hypotheses

18. First major hypotheses, Branching descent – species alive today came from species that lived in earlier times and that the lines of descent form a branched pattern resembling a tree

19. Second major hypotheses, (natural selection) – parents having genotypes that favor survival and reproduction leave more offspring, on average, than parents having less favorable genotypes for the same traits.

20. Natural Selection
Agents of selection can include predators, diseases, environmental extremes, ability to obtain food, and potential mates (of the opposite sex).

21. Natural Selection Survival of the fittest
Selection by potential mates is called SEXUAL SELECTION.
FITNESS DEFINED: The relative number of viable offspring left by each genotype.
Survival of the fittest

22. A GREAT DEAL OF EVIDENCE SUPPORTS DARWIN'S IDEAS

23. Evidence Earth is 4.5 Billion years old
Organisms have inherited Earth for most of its history
All organisms living today evolved from earlier, simpler life-forms

24. Evidence
Paleontologists-scientists who study fossils and can determine the age of fossils
They have dated these fossils to get an accurate evolutionary pattern

25. Evidence
Vestigial structures-structures that are evidence of an organisms evolutionary past, but are not used today
Appendix, Tail bone, gills in human embryoes

26. Evidence Homologous structures-structures that share a common ancestry
Limbs in mammals

27. How does this evolution occur?
Gradualism-model of evolution in which gradual change over a long period of time leads to species formation
Punctuated Equilibrium-Periods of evolution marked by periods of little or no change and then an explosion of change

29. Darwin's theory became accepted because it explained the available evidence better than any previous theory.
Natural selection can explain MIMICRY while earlier theories could not: many species survive because they resemble other, unrelated species that predators avoid.
Selection by predators perpetuates the best mimics and eliminates the less effective ones.

30. Industrial melanism among moths demonstrates natural selection:
The frequency of dark-colored moths varies geographically with levels of soot pollution.
Experiments with bird predators confirms that predators eat the non-camouflaged moths much more often than those which resemble their background.

31. Industrial Melanism
Mimicry –Warning Coloration

34. Branching descent with modification explained the facts of geographic distribution much better than any previous theory
The theory also explained HOMOLOGIES structures which resembled one another in their construction among related species, despite differences in adaptive use in many cases; earlier theories could not explain homologies so well
Some homologies include embryonic characters; others include functionless VESTIGIAL organs

35. Homology
Shared similarities are evidence that the organisms in question share a common ancestry

36. Homologies among mammalian forelimbs

37. The fossil record was poorly known in Darwin's time, but fossils discovered since then have in most cases fit well into branching patterns of descent with modification.
The ages of fossils are determined by both relative and absolute dating methods.
As an example: mollusks of the class Cephalopoda (squids, octopus, extinct ammonites, etc.) all fit into a pattern of branching descent, and their shared adaptations and anatomical features are all consistent with this pattern of descent.

38. REPRODUCTIVE ISOLATION consists of all biological mechanisms (not mere geographical separation) that prevent the interbreeding of natural populations.

39. REPRODUCTIVE ISOLATING MECHANISMS can act either before or after mating.
These mechanisms include isolation by differences in ecology, differences in mating seasons, differences in behavior, differences which prevent sexual parts from fitting together, or incompatibilities that make gametes, fertilized eggs, embryos, larvae, or adult hybrids inviable or sterile.

40. HOW NEW SPECIES ORIGINATE
Most new species originate after a period of geographic separation by an extrinsic barrier.
If the barrier lasts long enough for the populations on either side to diverge, then one or more reproductive isolating mechanisms will result.

41. GEOGRAPHIC SPECIATION- THE EVOLUTION OF REPRODUCTIVE ISOLATION DURING GEOGRAPHIC ISOLATION

42. There is good evidence that evolution continues to take place
Natural selection brings about seasonal fluctuations in the characteristics of fruit flies and Galapagos finches
Agricultural and industrial societies have greatly changed the selective forces operating on human populations
Evolution continues to take place wherever natural selection occurs, meaning whenever mortality differs according to genotype or phenotype

43. Discovery (1) Fixed species
Michelangelo’s fresco on the ceiling
of the Sistine Chapel
Presenter notes: So let’s start by thinking about the discovery of Evolution. Beginning in Classical times and persisting until long after the Renaissance, scientists thought species were fixed and unchangeable (or ‘immutable’ to use the language of the era). Their reasoning ran something like this: if God’s creation was perfect from the start, why would He bother to tinker with it at a later date?
en.wikipedia.org/wiki/The_Creation_of_Adam
From Classical times until long after the Renaissance, species
were considered to be special creations, fixed for all time. 43

44. Discovery (2): Transmutation
Around 1800, scientists began to
wonder whether species could
change or transmute.
Lamarck thought that if an animal
acquired a characteristic during its
lifetime, it could pass it onto its
offspring.
Hence giraffes got their long necks
through generations of straining to
reach high branches.
Presenter notes: However, around 1800, some scientists began to wonder if species could change their form or ‘transmute’. One of the early proponents of this idea was French scientist, Jean Baptiste de Lamarck ( ). If species were able to change their form over time, then how did it happen? Lamarck thought that if an animal acquired a characteristic during its lifetime, it could pass it onto its offspring. One of his favorite examples was the giraffe. In his view, the giraffe got its long neck through straining to reach the leaves on high branches, and this characteristic got passed down the generations. Most scientists of his day thought that Lamarck was wrong. At that time, only a few radical thinkers like Charles Darwin’s grandfather, Erasmus, agreed that species could change over time.
Jean Baptiste de Lamarck
commons.wikimedia.org/wiki/Image:Jean-baptiste_lamarck2.jpg
en.wikipedia.org/wiki/Image:Giraffe_standing.jpg 44

45. Discovery (3): Fossils and Strata
ImageWilliam_Smith.g.jpg
Geological_map_of_Great_Britain.jpg
Presenter notes: About the same time that these radical thinkers were discussing the transmutation (or evolution) of species, geologists like William Smith were beginning to map the rocks and fossils of Britain. Smith and others were able to show that rocks were laid down in a certain order and that the different fossils in different layers lived at different intervals of geological time. Here was clear evidence that different species had existed in the past compared with today. However, Smith did not go on to ask the question, ‘Why?’ or to consider that this might be evidence for evolution.
William Smith, his geology map & some of his fossil specimens
At about the same time, geologists like William Smith were
mapping the rocks and fossils of Britain. He and others showed
that different species existed in the past compared with today. 45

46. Discovery (4): Darwin’s Voyage
From , a
young naturalist called
Charles Darwin toured
the world in HMS
Beagle.
He was dazzled by the
amazing diversity of
life and started to
wonder how it might
have originated
Presenter notes: In the early nineteenth century, Charles Darwin ( ) rekindled ideas about evolution. In a sense, Evolution was in Darwin’s blood because, as we’ve already noted, his grandfather was an early supporter of the concept. From , Darwin toured the world on HMS Beagle as a young naturalist. He was dazzled by the amazing diversity of life, including some amazing fossils such as rodents the size of hippopotamuses and started to wonder how it might have originated.
Voyage of the Beagle
en.wikipedia.org/wiki/Image:Charles_Darwin_by_G._Richmond.jpg
en.wikipedia.org/wiki/Image:HMS_Beagle_by_Conrad_Martens.jpg 46

47. Discovery (5): Survival of the Fittest
In his Origin of Species,
published in 1859, Darwin
proposed how one species
might give rise to another.
Where food was limited,
competition meant that only
the fittest would survive.
This would lead to the natural selection
of the best adapted individuals and
eventually the evolution of a new species.
Natural Selection
explains adaption
Presenter notes: On his return from the Beagle the jigsaw pieces started to fit together in his mind. Around 1842 Darwin read an essay about human population growth by Malthus. Malthus had argued that human population would grow more quickly than food supply. Consequently competition for food would become intense and only the fittest and most able would survive. Darwin applied these ideas to all of life and came up with his now famous concept of Natural Selection. Darwin reasoned that if an organism possessed a character that improved its chances of survival, then it would be more likely to pass on that character to the next generation. Therefore organisms would become progressively adapted to their environment, leading to the evolution of new species. Darwin published this idea in his “Origin of Species by means of Natural Selection” in 1859.
Darwin in 1860
en.wikipedia.org/wiki/Image:Darwin%27s_finches.jpeg 47

48. Discovery (6): Huxley v. Wilberforce
Darwin’s idea of
Evolution by Natural
Selection was met with
huge controversy.
A famous debate in
1860 pitted Bishop
Wilberforce against
Darwin’s bulldog,
Thomas Henry Huxley.
Presenter notes: However, Darwin’s concept of Evolution by Natural Selection was met with considerable controversy and debate. Although some Christians were willing to accept Evolution, if God was allowed to guide the process, most were opposed to the idea of Evolution being driven by random competition and natural laws. However, some leading scientists did embrace Evolution. One of these was Thomas Henry Huxley ( ), who became known as “Darwin’s bulldog” for his ferocious support of Darwin. On 30 June 1860, Huxley debated Evolution with Bishop Wilberforce at a British Association meeting in Oxford. In the debate, Wilberforce infamously inquired of Huxley whether it was through his grandfather or grandmother that he claimed descent from a monkey! Huxley then rose to the defence of Evolution, finishing his speech with the now legendary ‘put-down’ that he was not ashamed to have a monkey for his ancestor, but he would be ashamed to be connected with a man who used great gifts to obscure the truth! This debate saw many people come to accept Evolution. However, there was little support or enthusiasm for Darwin’s mechanism of Natural Selection.
Bishop Wilberforce v. T. H. Huxley
Evolutionists got the better of the debate, but few were convinced
by Darwin’s idea of Natural Selection. 48

49. Discovery (7): Genetics
From , a monk called Gregor
Mendel cultivated 29,000 pea plants
to investigate how evolution worked
i.e., how characteristics were passed
down the generations.
He figured out the basic principles of
genetics. He showed that offspring
received characteristics from both
parents, but only the dominant
characteristic trait was expressed.
Mendel’s work only came to light in
1900, long after his death
Mendel and his peas
Presenter notes: While all this was going on, and unbeknown to the scientific elite in Britain, an Austrian monk called Gregor Mendel ( ) was carrying out important experiments that would eventually prove that Darwin’s Natural Selection was in fact correct. For seven years, Mendel cross-bred different strains of pea plants to investigate how characteristics like the colour of the flowers got passed down the generations. In a quite amazing feat, he cultivated almost thirty thousand pea plants and in doing so figured out the basic principles of, what would later become known as, Genetics. He showed that offspring received characteristics from both parents, but only the dominant characteristic was expressed. This was contrary to the prevailing view at the time that the characteristics of both parents were somehow “blended” together. Unfortunately, Mendel’s work was overlooked by scientists in the West, only coming to light long after his death.
en.wikipedia.org/wiki/Image:Mendel.png
en.wikipedia.org/wiki/Image:Doperwt_rijserwt_peulen_Pisum_sativum.jpg 49

50. Discovery (8): Making Sense
In the early 20th century, scientist started to
make sense of how evolution worked.
Building on Mendel’s genetics, studies
showed how characteristics in a population
could be selected by environmental
pressures.
This Modern Synthesis, as Julian Huxley
called it, brought Darwin’s Natural Selection
back to the centre of evolutionary theory.
Presenter notes: When Mendel’s work on Genetics was finally “re-discovered” in 1900, it started to make sense of evolution in a new way and stimulated renewed interest in Darwin’s work of fifty years earlier. Building on Mendel’s work, studies showed how genetic traits in a population of animals or plants could be selected by environmental pressures and how a population could become progressively adapted to its environment. This Modern Synthesis, as Julian Huxley called it, brought Darwin’s concept of Natural Selection right back to the centre of evolutionary theory, as we will see in the next part of the talk.
Julian Huxley
and the
Modern Synthesis
en.wikipedia.org/wiki/Image:Hux-Oxon-72.jpg 50

51. Discovery (9): Opposition
Despite the achieval of
scientific consensus on
evolution, some Christian
groups continued to
oppose the concept.
In 1925, the teaching of
evolution was outlawed
in Tennessee, USA,
resulting in the infamous
Scopes Monkey Trial
Presenter notes: However, despite becoming universally accepted by the scientific community in the early 20th century, Evolution by Natural Selection continued to meet strong opposition by certain religious groups. This was especially true of Christian fundamentalists, who saw the concept as an erosion of God’s sovereignty. In 1925, the State of Tennessee, USA outlawed the teaching of Evolution completely. When one teacher, John Scopes, continued to teach evolution he was tried and found guilty in what is now infamously known as the “Scopes Monkey Trial”!
Outside the Scopes Trial 51

52. Discussion: Should Creationism and Evolution
be given equal time in science lessons?
Presenter notes: This religious opposition to Evolution has continued to the present day. However, today opposition to Evolution is often more subtle. For example several US states have recently argued that Evolution and Creationism should be given “equal time” in the Science classroom. Creationism maintains than a literal reading of the Book of Genesis in the Bible is the only adequate explanation for how Life came into being and that the concept of Evolution is incorrect. On the surface, this demand seems OK. After all, isn’t it fair to present both sides of the debate? Over the next few minutes, we’ll look at this issue at little more closely as we discuss this important question: should Creationism and Evolution should be given “equal time” in the Science classroom?
science.kukuchew.com/wp-content/uploads/
2008/01/stop_following_me_creationist.jpg 52

53. Mechanism (1): All in the Genes
The genetic make-up of
an organism is known as
its genotype.
An organism’s genotype
and the environment in
which it lives determines
its total characteristic traits
i.e. its phenotype.
Presenter notes: In this second part of the talk, we will think about the mechanism of evolution, or to put it more simply, how evolution works. Earlier, we’ve mentioned the importance of genetics in the discovery of Evolution, and we’ll think much more about that over the next few slides. But first of all, let’s introduce ourselves to a few technical terms. The genetic make-up of an organism is known as its genotype. The genotype of an organism and the environment in which it lives (nature and nurture together) determine the characteristic traits of the organism, or its phenotype.
Genotype
Phenotype
commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG 53

54. Mechanism (2): DNA The double-helix structure of DNA was discovered
in 1953.
This showed how
genetic information
is transferred from
one cell to another
almost without error.
Presenter notes: The genotype of an organism is stored in DNA molecules, which are a sort of information bank found within the nucleus of every cell. Every time an organism grows a new cell a new copy of the DNA is created. It is important that every copy of the DNA is identical, since any errors copying the genotype may prevent the cell from functioning properly. In 1953, Watson and Crick figured out that DNA had a helical structure and showed how it copies itself with such amazing accuracy. When DNA replicates, the helix unwinds and each strand produces an exact mirror image copy of itself. This ensures that each copy is identical to the original.
Watson and Crick and their model of DNA
DNA replication
en.wikipedia.org/wiki/DNA 54

55. Mechanism (3): Mutation
However, occasional
mutations or copying errors
can and do occur when
DNA is replicated.
Mutations may be caused
by radiation, viruses, or
carcinogens.
Mutations are rare and often have
damaging effects. Consequently organisms
have special enzymes whose job it is to
repair faulty DNA.
Types of mutation
Mutant fruitfly
Presenter notes: However, very occasionally, tiny copying errors can and do occur when DNA is replicated. These copying errors are called mutations. Mutations may be caused by a number of factors including radiation, viruses, or carcinogens (cancer-causing materials). As the genotype provides the blueprint for how each cell should grow and function, even a tiny mutation might mean that the cells fail to work properly. Take for example the common fruitfly: a single mutation in the fruitfly can change the colour of the eye from red (its normal colour) to white. White-eyed fruitfly are less successful at mating. Because of the potential for mutation, most organisms have a group of special enzymes whose job it is to go round and repair any faulty DNA.
upload.wikimedia.org/wikipedia/commons/7/79/Types-of-mutation.png humansystemstherapeutics.com/bb.htm 55

56. Mechanism (4): Variation
Nevertheless, some
mutations will persist and
increase genetic variation
within a population.
Variants of a particular
gene are known as alleles.
For example, the one of
the genes for hair colour
comprises brown/blonde
alleles.
Presenter notes: Mutations give rise to variants, or alleles, of the same gene. One person may have one set of alleles, and another person, a different set. For example, take hair colour in humans. One of the genes that codes for hair colour occurs as two alleles, brown and blonde. If you throw you mind back to earlier in this talk you’ll remember how Mendel showed that one allele is usually dominant and the other recessive. In the case of hair colour, brown is dominant and blonde is recessive. So if a person gets a brown allele from one parent and a blonde allele from the other parent, they will have brown hair. A person will only have blonde hair where they receive blonde alleles from both parents.
majorityrights.com/index.php/weblog/comments/racial_variation_in_some_parts_of_the_skull_involved_in_chewing/ 56

57. Mechanism (5): Natural Selection
Mutant alleles spread through a
population by sexual reproduction.
If an allele exerts a harmful effect,
it will reduce the ability of the
individual to reproduce and the
allele will probably be removed
from the population.
In contrast, mutants with favorable
effects are preferentially passed on
Selection of dark gene
Presenter notes: If a person, or any other organism for that matter, develops a new allele (a mutation), they can spread this around the population by sexual reproduction. However, if the allele exerts a harmful effect on the individual then this will reduce the likelihood of it reproducing and the allele will be removed from the population. Only those mutant alleles that have beneficial effects that increase the likelihood of reproduction will be passed on to offspring. In this way, harmful alleles are removed from a population while favorable alleles accumulate. This is Darwin’s concept of Natural Selection and shows how a population adapts to its environment over time.
en.wikipedia.org/wiki/Image:Mutation_and_selection_diagram.svg 57

58. Mechanism (6): Peppered Moth
Haldane and the peppered moth
The Peppered Moth is an
example of Natural Selection
in action discovered by Haldane
During the Industrial Revolution
the trees on which the moth
rested became soot-covered.  
Presenter notes: The case of the Peppered Moth is an excellent example of Darwin’s Natural Selection in action put forward by the biologist J.B.S. Haldane in The gene that controls the colour of the Peppered Moth occurs as two alleles, a mottled allele (pale colour) and a melanic allele (black colour). Early in the 18th century, pale moths were dominant in the countryside around Manchester. However, during the Industrial Revolution the trees on which the moths rested became covered in black soot. Pale mottled moths were poorly camouflaged on the black tree trunks and were preferentially eaten by birds. In contrast, the black melanic moths were better at avoiding predation. Natural Selection acted against the pale moths and in only a few generations, the melanic moths were dominant. However, there was one final twist. As the skies of Manchester became cleaner in the 20th century, the mottled moths made a comeback and displaced the melanic moths again.
This selected against the allele for pale
colour in the population (which were
poorly camouflaged from predators)
and selected for the dark colour allele.
en.wikipedia.org/wiki/Image:Biston.betularia.f.carbonaria.7209.jpg
en.wikipedia.org/wiki/J._B._S._Haldane 58

59. Mechanism (7): Microevolution
The dog is another example of how
selection can change the frequency
of alleles in a population.
Dogs have been artificially selected
for certain characteristics for many
years, and different breeds have
different alleles.
All breeds of dog belong to the same
species, Canis lupus (the wolf) so this
is an example of Microevolution as no
new species has resulted.
Presenter notes: The case of the Peppered Moth shows how natural selection can change the frequency (or relative proportion) of alleles in a population. A more straightforward example of the same phenomenon is the breeding of dogs. Humans have been breeding dogs for thousands of years and trying to develop certain characteristics. This “artificial selection” is exactly the same process as natural selection but controlled by human intention rather than natural forces. Although humans have been successful in changing the frequency of alleles in different dog breeds, they haven’t created new species. The definition of a species is a population that can interbreed and produce fertile offspring. Most dogs can successively interbreed with other dogs, and also with wolves, so in actual fact all dog breeds are just subspecies of the wolf, Canis lupus! Dog breeding is therefore an example of what biologists called Microevolution; the frequency of alleles in the population have changed, but not greatly enough to give rise to a new species.
Dogs are wolves 59

60. Mechanism (8): Macroevolution
However, if two populations of a
species become isolated from
one another for tens of thousands
of years, genetic difference may
become marked.
If the two populations can no-longer
interbreed, new species are born.
This is called Macroevolution.
Darwin’s Galapagos finches are
an example of this process in action.
Galapagos finches
Presenter notes: To give rise to a new species, Microevolution needs to go on for more much longer than humans have been breeding dogs. For example, if a species was to become divided into two isolated populations for tens of thousands of years, then natural selection would eventually change the frequency of alleles to such an extent that members of the two populations could no longer interbreed. This process would result in the birth of new species or speciation. Where speciation occurs, biologists refer to the process as Macroevolution. An excellent example of Macroevolution is that observed by Charles Darwin during his world tour on HMS Beagle. When visiting the Galapagos Islands in the Pacific Ocean he noticed that each island had its own distinctive species of finch. Darwin argued that the islands had originally been colonized by just one species of finch, but then in isolation, each island population had evolved in response to different environmental conditions. 60

61. Mechanism (9): Speciation Today?
The mosquito was introduced to
the London Underground during
its construction around 1900.
It became infamous in the War
for attacking people sheltering
from the Blitz.
Studies indicate several genetic
differences from its above-ground
ancestors. Interbreeding between
populations is difficult suggesting
that speciation may be occurring.
London Underground Mosquito
Presenter notes: An obvious question as we conclude our look at how evolution works is: are there any examples of evolution by natural selection going on today. Obviously, the answer is yes, as all species are undergoing evolution. However, as the rate of change is very slow, examples are very difficult to detect and even harder to prove. One possible example is the case of the ‘London Underground Mosquito’. This mosquito found its way into the Tube system around 1900 when the railway lines were being constructed. It became infamous during the Second World War as it would constantly bite people sheltering from the Blitz. The London Underground Mosquito has been isolated from the surface for over a hundred years and studies indicate that there are already genetic differences between it and its above-ground relatives. The differences are so great that the two populations have difficulty interbreeding. Perhaps here is an example of ongoing speciation today?
en.wikipedia.org/wiki/Image:Gb-lu-Angel-southbound.jpg
en.wikipedia.org/wiki/Culex 61

62. Activity Natural Selection in the Peppered Moth
Presenter notes: We’ve already discussed the case of the Peppered Moth as an example of Natural Selection in action. In this next activity we’ll look more closely at the Peppered Moth and discover how natural selection works in detail.
en.wikipedia.org/wiki/Image:Biston.betularia.f.carbonaria.7209.jpg 62

63. Evidence (1): Biochemistry
The basic similarity of all living things suggests
that they evolved from a single common ancestor.
As we have already seen, all living things pass
on information from generation to generation
using the DNA molecule.
All living things also use a molecule
called ATP to carry
energy around the
organism.
Presenter notes: In this third and final part of the talk, we’ll consider the evidence for evolution and reflect on the fact that Biology simply doesn’t make sense if we take Evolution out of the equation. One of the most striking pieces of evidence for evolution is the basic similarity of all living things. First of all, as we’ll already stressed, all living things pass on genetic information from generation to generation using the DNA molecule. However another basic shared characteristic is the use of the ATP molecule to carry energy around the cell. These two fundamental similarities suggest that all living things evolved from a single common ancestor.
DNA for
Information Transfer
ATP for
Energy
Transfer
en.wikipedia.org/wiki/Image:ATP-xtal-3D-sticks.png 63

64. Evidence (2): Similar Genes
HUMAN CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCACGACTGTTGAACGA
CHIMPANZEE CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCATGACTGTTGAACGA
GORILLA CCAAGGTCACAACTACTCCAATTGTCACAACTGTTCCAACCGTCACGACTGTTGAACGA
Genetic code of chimps and gorillas is almost identical to humans
If evolution is true then we might also expect that closely
related organisms will be more similar to one another than more
distantly related organisms.
Comparison of the human genetic code with that of other
organisms show that chimpanzees are nearly genetically identical
(differ by less than 1.2%) whereas the mouse differs by ≈15%.
Presenter notes: If life was generated through evolution then we might also predict that closely related organisms will be more similar to one another than more distantly related organisms. This is borne out by comparison of the human genetic code with that of other organisms. These studies show that chimpanzees, our closest relations, are nearly genetically identical (their genes differ by only 1.2%) whereas the more distantly related mouse differs by some 15%. 64

65. Evidence (3): Comparative Anatomy
Similar comparisons can be made
based on anatomical evidence.
The skeleton of humans and
gorillas are very similar suggesting
they shared a recent common
ancestor, but very different from the
more distantly related
woodlouse…
yet all have a common
shared characteristic:
bilateral symmetry
Presenter notes: Very similar comparisons can be made based on anatomical evidence. For example the skeleton of humans is very similar to that of the gorilla, our close relative, but both are very different from the exoskeleton of the woodlouse. Yet even primates and woodlice share some basic anatomical characteristics such as bilateral symmetry suggesting that they are all related in the Tree of Life, albeit distantly. Here again is clear evidence for the inter-relatedness of all living things.
Human and Gorilla
Woodlouse
en.wikipedia.org/wiki/Image:Primatenskelett-drawing.jpg 65

66. Evidence (4): Homology The pentadactyl limb is ancestral to all
vertebrates…
Presenter notes: Another piece of evidence that supports evolution is the concept that biologists have called homology. Homology refers to an anatomical feature possessed by an ancestor that has subsequently been modified by its descendents for a specific function. Take, for example, the pentadactyl (or five fingered) limb. This is found in all vertebrates from fish to amphibians to reptiles to mammals to birds. This structure is easily recognizable in all these diverse groups of organisms but has been adapted to suit particular purposes in each. So we find it adapted as wings for flight in birds, as fins for swimming in fish, as scrapers for digging amongst moles and so on. As all these diverse organisms have the same anatomical blueprint, this strongly suggests they are inter-related.
but modified for different uses
en.wikipedia.org/wiki/Image:Evolution_pl.png 66

67. Evidence (5): Vestigial Structures
As evolution progresses, some
structures get side-lined as they
are not longer of use. These
are known as vestigial structures.
The coccyx is a much reduced
version of an ancestral tail, which
was formerly adapted to aid
balance and climbing.
Another vestigial structure in
humans is the appendix.
Presenter notes: Whilst ancestral anatomical features can be adapted to new purposes (as we’ve just seen), they can also find themselves redundant altogether. Features that get sidelined by evolution in this way are called Vestigial Structures. One example is the human coccyx or tail bone which is a much reduced version of a bony tail possessed by our ancestors. Formerly adapted to aid balance and climbing, a tail has little function in human behaviour so has been selected against. It probably has been retained in a vestigial form because it has some use as a point for muscle attachment in the bottom. Another example of a vestigial human organ is the appendix.
The coccyx is a vestigial tail
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68. Evidence (6): Fossil Record
en.wikipedia.org/wiki/Image:Eopraptor_sketch5.png
© World Health Org.
Presenter notes: All the pieces of evidence that we have discussed so far point to the inter-relatedness of all living things and their evolution from a single common ancestor. However, perhaps the most compelling piece of evidence in support of evolution is the fossil record itself. The fossil record shows a sequence from simple bacteria in the oldest rocks through to more complicated organisms like dinosaurs and humans in much younger rocks. It shows that different species arose at different times and, as we see in the next slide, in many cases there are clear transitions from one species, or group, to another.
Background note: A companion talk on the History of Life can be downloaded from the Your Planet Earth website:
© NASA
origins
bacteria
complex cells
dinosaurs
humans
The fossil record shows a sequence from simple bacteria to
more complicated organisms through time and provides the most
compelling evidence for evolution. 68

69. Evidence (7): Transitional fossils
Many fossils show a clear
transition from one species,
or group, to another.
Archaeopteryx was found
in Germany in It
share many characteristics
with both dinosaurs and
birds.
It provides good evidence
that birds arose from
dinosaur ancestors
Presenter notes: One of the most famous examples of a species that is transitional between two major groups, is the 150 million year old Archaeopteryx. Archaeopteryx has several characteristic features seen in certain dinosaurs including teeth and a bony tail. However, it has more features that are characteristic of modern birds such as a wishbone, wings with flight feathers, and a partially reversed first toe. Although geologists classify Archaeopteryx as an early fossil bird they recognize that it is more closely related to the dinosaurs than any birds living today. Archaeopteryx therefore provides good evidence of the evolutionary transition from dinosaurs to birds.
Archaeopteryx
en.wikipedia.org/wiki/Image:Archaeopteryx_lithographica_paris.JPG 69

70. Evidence (8): Geography
Geographic spread of
organisms also tells of
their past evolution.
Marsupials occur in
two populations today
in the Americas and
Australia.
This shows the group
evolved before the
continents drifted apart
Marsupials
Presenter notes: A rather different source of evidence in support of evolution comes from the geographic distribution of species today. If we take for example the case of marsupials, we see that this primitive group of mammals is found in the Americas and Australasia. Marsupials are not renowned as strong swimmers so this raises the questions as to how two populations came to be separated by the Pacific Ocean if they evolved from a common ancestor. However, this problem is resolved if we remember that the Earth’s continents have not remained stationary over time but have drifted around the surface of the Earth. During the Jurassic Period, 160 million years ago, all the Southern Hemisphere landmasses were joined together and you could have walked from Australia to South America across what is present day Antarctica. Fossil evidence shows that marsupials evolved in the Jurassic but after the continents started to break-up, the marsupials must have got separated into two populations, one in the Americas and the other in Australasia. In fact fossil marsupials have even been found in Antarctica and South Africa as well, providing evidence that that these continents acted as a land bridge connecting the two populations for a time.
evolution.berkeley.edu/evosite/lines/IVCexperiments.shtml
en.wikipedia.org/wiki/Image:Kangaroo_and_joey03.jpg 70

71. Evidence (9): Antibiotic resistance
Staphylococcus
We are all familiar with
the way that certain
bacteria can become
resistant to antibiotics
This is an example of natural selection in
action. The antibiotic acts as an
environmental pressure. It weeds out
those bacteria with low resistance and
only those with high resistance survive
to reproduce.
Presenter notes: A final and perhaps especially convincing piece of evidence for evolution is the familiar way that bacteria may become resistant to antibiotics. Bacteria have a fast life cycle and can produce a new generation every 4 hours. As natural selection acts on each generation this means bacteria can rapidly respond to environmental pressures. In effect the antibiotics act to weed out those bacteria with low resistance in each generation. Only bacteria with high resistance survive and pass their alleles to the next generation. Consequently, in just a short time, natural selection increases the resistance level of the bacteria population. This is an example of evolution in action amongst the simplest organisms on our planet – and then having an impact on the most complex organisms!
en.wikipedia.org/wiki/Image:Staphylococcus_aureus%2C_50%2C000x%2C_USDA%2C_ARS%2C_EMU.jpg 71

72. Evolution
Presenter notes: In this talk we have discussed how Evolution was first discovered, how Evolution works, and last of all, the evidence for Evolution. In particular, we’ve reflected on the fact that Biology simply does not make sense when Evolution is taken out of the equation. In addition, we’ve noted that while aspects of Evolution remain theoretical, that Evolution is happening is an established fact, through great quantities of excellent evidence. Yet, outside the scientific community, surveys show that in the USA, 40% of people do not believe in Evolution by Natural Selection, and even in the UK, some 21% are said to be doubtful. As we close, discuss why non-scientists are reluctant to accept Evolution. Do you think that Evolution is a threat to religions like Christianity? Have scientists been inadequate in the way they have communicated Evolution? Is our science education system at fault? How could understanding of Evolution be improved amongst the public at large?
commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG
commons.wikimedia.org/wiki/Image:Charles_Darwin_1881.jpg 72