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Evidence for evolution. In the early 1800’s prevailing belief was that: organisms were specially created and unchanged since their creation Species created independently of each other Earth not old. Ussher’s estimate: for Earth’s creation 4004 BC. Lamarck.

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Evidence for evolution

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evidence for evolution
Evidence for evolution
  • In the early 1800’s prevailing belief was that:
    • organisms were specially created and unchanged since their creation
    • Species created independently of each other
    • Earth not old. Ussher’s estimate: for Earth’s creation 4004 BC
  • Fact of evolution proposed in late 1700’s early 1800’s.
  • Jean Baptiste Lamarck 1809, 1815 proposed that all species were derived by gradual evolution from other species.
  • Lamarck’s idea was that evolution was driven by an innate tendency of organisms to become more complex over time.
inheritance of acquired characteristics
Inheritance of Acquired Characteristics
  • Lamarck’s proposed mechanism of evolution was called the Inheritance of Acquired Characteristics (IAC)
  • IAC suggested that modifications to organisms during their life could be passed on to their offspring (e.g., a giraffe stretching its neck during its life passes slightly longer neck to offspring).
inheritance of acquired characteristics4
Inheritance of Acquired Characteristics
  • Obviously, Lamarck’s ideas about the mechanism of evolution largely contradict current biological knowledge.
  • The information required to build a body is stored in DNA and that information (influenced by the environment) determines the phenotype. Changes to the phenotype during life however do not affect the DNA sequence. Information flow is thus only in one direction from DNA  phenotype, not in the reverse direction.
  • However, recent research in the emerging field of epigenetics shows that Lamarckian effects may occur through changes in the control of gene expression caused by environmental effects e.g. food shortage during development.
  • Epigenetics is the study of heritable changes in gene expression caused by mechanisms other than changes in the DNA sequence.
  • The DNA nucleotide sequence is not changed but whether and how much genes are expressed can be altered and some of these changes may be passed from one generation to another.
  • One way in which epigenetic effects have been shown to occur is through environmentally induced methylation in which a methyl group (CH3) is added to cytosine nucleotides converting them to 5-methyl-cytosine.
  • More heavily methylated regions are translated and transcribed less frequently than non-methylated regions.
  • One well documented example of epigenetic effects resulted from the Dutch winter famine of 1944/45 at the end of WWII.
  • The children of women pregnant during the famine were born smaller than normal (which was to be expected).
  • However, the children of those children were also born smaller than average. This suggests the famine induced epigenetic changes in mothers pregnant during the famine that were passed to their offspring.

Charles Darwin


“On the origin

of species”

in 1859.

charles darwin 1809 1882
Charles Darwin (1809-1882)
  • Son of a wealthy doctor.
  • Dropped out of medical school.
  • Studied theology, but was much more interested in natural history (e.g. he had a large insect collection).
  • After college signed on as captain’s companion on TheBeagle.
voyage of the beagle
Voyage of the Beagle
  • Darwin companion for Captain Fitzroy on

Voyage of The Beagle (1831-1836).

  • The Beagle’s mission was to map the coast of South America, but the ship traveled around the World.
  • Sites visited included Galapagos Islands a group of volcanic islands (hence of recent origin) off the coast of Ecuador.

Unique animals on Galapagos include

giant tortoises, marine iguanas, and

Darwin’s finches.

Galapagos Giant Tortoise






influence of geological thinking on darwin
Influence of geological thinking on Darwin
  • By the time of “The Beagle” voyage the idea that Earth was young was being challenged.
  • Opposition based on principle of Uniformitarianism.
  • This is the idea that geological processes happening today are the same as have operated in the past.
influence of geological thinking on darwin17
Influence of geological thinking on Darwin
  • Uniformitarianism contrasted with Catastrophism which proposed that current geological formations had resulted from catastrophic events (such as the biblical flood) which occurred on scale unknown today.
  • Uniformitarianism first proposed by James Hutton and championed by Charles Lyell.
influence of geological thinking on darwin18
Influence of geological thinking on Darwin
  • During the voyage Darwin read Lyell’s new book “Principles of Geology.”
  • Lyell emphasized two points:
  • 1. Gradualism: Geological features can be explained by the slow gradual action of processes we observe every day e.g. erosion by wind and water, deposition of sediments in rivers.
  • 2. The Earth is very old: there has been lots of time for change to occur.
influence of geological thinking on darwin19
Influence of geological thinking on Darwin
  • Hutton and Lyell inferred Earth must be very old based on measurements of rate of ongoing rock forming processes (e.g. deposition of mud and sand).
  • These developments in geology focused Darwin on the potential importance of gradual change in shaping structures.
what darwin observed
What Darwin observed
  • On the voyage Darwin noted many things that were puzzling from the point of view of a creationist explanation for the diversity of life.
what darwin observed21
What Darwin observed
  • 1. South American fossils resembled living South American animals.
  • 2. Parts of the world with similar habitats and climates (e.g. Australia and South America) are populated by very different animals.
  • 3. Plants and animals on each continent are different from those on other continents.
  • 4. Many species on remote oceanic islands are found only there (endemic).
  • 5. Endemic species on islands closely resemble species found on adjacent mainland.
what darwin observed22
What Darwin observed
  • These observations taken together don’t make sense if organisms were specially created.
    • Why should similar habitats in different parts of the world have different faunas?
    • Why should remote islands have unique faunas that differ from but resemble those on adjacent land masses?
  • Together these observations suggested to Darwin that species change over time i.e., that evolution occurs.
darwin and wallace
Darwin and Wallace
  • After returning from the voyage Darwin spent more than 20 years developing his ideas and gathering the evidence to support them.
  • In 1858 Charles Darwin and Alfred Russel Wallace jointly proposed natural selection as the primarymechanism by which evolution takes place.
  • In 1859 Darwin published his book On the Origin of Species, which summarized his ideas about evolution and presented the evidence to support them.
the modern synthesis
The “modern synthesis”
  • Idea of evolution was accepted rapidly by scientists.
  • Lack of understanding of heredity and population genetics, however, prevented natural selection being accepted as the principal mechanism of evolution until 1930’s.
  • The “Modern Synthesis” in the 1930’s of combined the ideas of population genetics and natural selection to explain gradual evolution, speciation, and macroevolution.
evidence for evolution25
Evidence for Evolution
  • Evidence of change in organisms over time
  • An example in a living species:
    • evolution of beak length in soapberry bugs.
    • Soapberry bugs use long beak to penetrate seeds in fruits and eat them.
    • Native host plant is balloon vine which has thick fruits.
evolution of soapberry bugs
Evolution of Soapberry Bugs
  • In 1926 flat-podded Golden rain tree introduced to Florida. Has thin fruits.
  • Today soapberry bugs feeding on Golden rain trees have much shorter beaks than those living on balloon vines.

Comparison of beak

lengths in areas

with and without

golden rain trees


Data from museum

specimens documents

change in beak length

over time.

antibiotic resistance in bacteria
Antibiotic resistance in bacteria
  • In 1947 only four years after the mass production of penicillin began resistant strains of Staphylococcusaureus began to be reported.
  • Antibiotic resistance is now widespread and in the US half of all S. aureus infections are resistant to multiple antibiotics including penicillin, tetracycline, erythromicin and methicillin.
antibiotic resistance
Antibiotic resistance
  • Bacteria have evolved resistance quickly in part because of their rapid reproduction, but also because antibiotics were misused (e.g. by being overprescribed or prescribed for non-bacterial infections and by people not completing their course of antibiotics)
the evidence for evolution
The evidence for evolution
  • Fossil evidence
  • Vestigial structures
  • Homologous structures
  • Atavistic structures
  • Other evidence
    • Jerry-rigged structures
    • Adaptive radiation
    • Artificial selection
fossil evidence
Fossil evidence
  • Fossils are mineralized copies of the remains of organisms preserved in sedimentary rocks.
  • In the process of fossilization a dead organism is covered by sediment and the organic matter is replaced by minerals leaving behind an impression of the organism.
fossil evidence of evolution
Fossil evidence of evolution
  • Millions of fossils have been collected and it is clear from fossil evidence that many species (in fact almost all that have ever existed) have become extinct.
  • Equally clearly the faunas of different geological eras are very different and have changed over time.
fossil evidence of evolution34
Fossil evidence of evolution
  • Law of Succession: Fossil and living organisms in same area are related to each other and differ from organisms in other areas.
  • South America contains both fossil and living armadillos

Extinct glyptodont (2,000 kg) resembles the

modern-day South American armadillo (2 kg).

fossil evidence of evolution36
Fossil evidence of evolution
  • Similarly modern Australia is filled with marsupials and fossils in Australia are of similar marsupial forms.
  • Extinct short-faced kangaroo.


fossil evidence of evolution37
Fossil evidence of evolution
  • Transitional forms
  • If fossil organisms are ancestral to modern organisms then there should be transitional fossils that show characteristics intermediate between the older and more recent groups.
  • Archaeopteryx the oldest known fossil bird (name means “ancient wing) has mix of reptilian and avian features.
  • Reptilian: long tail, teeth, long clawed fingers
  • Avian: feathers, ribs with uncinate processes, avian shoulder girdle.


(oldest known

fossil bird)



evolution of mammals
Evolution of mammals
  • There are numerous excellent fossil series that document the transitions from ancestral species to later species.
  • For example: the evolution of mammals from synapsid reptiles.
  • An extensive series of fossils documents the changes in the synapsid lower jaw from a jaw made of multiple bones to the modern mammals single dentary and the incorporation of some synapsid jaw bones into the inner ear.
tiktaalik roseae
Tiktaalik roseae
  • Another example is the evolution of the first amphibians from lobe finned fishes.
  • The transitional fossil Tiktaalik roseae possesses an intermediate suites of characters.
  • It has fish-like scales, palate and jaws, but an amphibian-like mobile neck and head, an ear that could hear in air, and the bones in its fins are intermediate between those of fish such as Eusthenopteron and Panderichthys and early amphibians such as Acanthostega.


vestigial structures
Vestigial structures
  • Many organisms possess rudimentary or functionless versions of body parts that function in close relatives/ancestors.
  • The fact that structures are rudimentary implies they had ancestors in which these structures were functional. This suggests an evolutionary history.
examples of vestigial structures
Examples of Vestigial structures
  • Cave populations of Mexican tetra fish have eye sockets, but no eyes.
  • Kiwis have tiny, stubby wings
  • Boas have tiny remnant hind limbs


human vestigial structures
Human vestigial structures
  • Coccyx: vestigial tailbone at base of spine.
  • Arrector pili muscle at base of hair follicles makes hair stand up.
  • Appendix: reduced in size. Used in digestion of cellulose in herbivores e.g. rabbits.
vestigial developmental traits
Vestigial developmental traits
  • Adult chickens: three bones in forefoot (wing), four in hindfoot.
  • However, digit 5 appears briefly during embryonic development before disappearing.
molecular vestigial traits
Molecular vestigial traits
  • Human genome contains large numbers of pseudogenes that do not code for functional RNA or proteins. These are leftovers from evolutionary history once functional genes that have been turned off.
  • E.g. there are several pseudogenes of hemoglobin. May be as many as 6,000 pseudogenes in human genome.
homologous structures
Homologous structures
  • Homologous structures are those constructed from the same basic components which have been inherited from a common ancestor and then modified for different purposes.
  • E.g. The forelimbs of a human, mole, horse, dolphin and bat are constructed from the same bones, but the bones differ in size and shape and the structures made from the bones are used in radically different ways.
homologous structures55
Homologous structures
  • Homologous structures make no sense if organisms were specially created, but they do if a set of organisms share a common ancestor and all inherited the same basic bone structure from that ancestor.
  • Homologous structures imply an evolutionary history and common ancestry.

Homologous structures (i.e. derived from a common ancestor). Even though the

forelimbs have evolved to carry out very different tasks they are all constructed

from the same bones.

FIG 2.11

homology vs convergent evolution
Homology vs. Convergent Evolution
  • Not all similarities between different species are due to homology.
  • The streamlined shapes of sharks and whales are not a due to common ancestry but to convergent evolution.
  • The same selection pressures to be able to swim efficiently in water have independently produced similarly shaped bodies instead of the traits being inherited from a recent common ancestor.
homology vs convergent evolution58
Homology vs. Convergent Evolution
  • Whales and dolphins evolved from terrestrial ancestors about 50 million years ago, whereas shark fossils as much as 350 million years old are known.
  • The whales are most closely related to artiodactyls (hoofed mammals that include deer and hippos) and both whales and deer evolved from hoofed, carnivorous ancestors.




homologous vs analagous structures
Homologous vs. Analagous structures
  • Similarly, the wings of butterflies and birds are not homologous (because their structural components were not derived from a recent common ancestor) but perform the same function.
  • Such structures are analagous. They carry out the same function.
molecular homology
Molecular Homology
  • All organisms (with a few minor exceptions) use the same genetic code to specify which sequences of bases specify which amino acids when assembling proteins.
  • The reason the code is essentially universal is that a mutation that altered the code would alter almost every protein produced and so would be lethal.

Figure 1.1.1. The standard genetic code and known variant nuclear codes. 

(1) Candida, a unicellular yeast. (2) Micrococcus. (3) ciliated protozoans and green algae.

(4) Mycoplasma. (5) suppressor codon in bacteria. (6) Euplotes.

(7) the selenocysteine codon (8) Spiroplasma. (9) Micrococcus.

(10) resume codon in ssrA RNA (Lehman 2001).


molecular homology genetic flaws shared by different species
Molecular Homology: Genetic flaws shared by different species
  • Chromosome 17 in humans PMP22 gene has duplicate sequence of DNA (CMT1A repeat) on either side of it.
  • It is the result of duplication and insertion of DNA and occasionally causes inaccurate crossing over during meiosis.
molecular homology65
Molecular Homology
  • Humans share CMT1A repeat with bonobos and chimpanzees, but not gorillas, orang-utans or other primates.
  • Suggests CMT1A derived from common ancestor of bonobos, chimps and humans.
atavistic traits
Atavistic traits
  • Atavistic traits are anatomical “throwbacks” that occasionally occur when a feature present in an ancestor reappears in a modern organism.
  • For example, occasionally horses are born that have additional toes either side of their hoof. Similarly, sometimes people are born with a short tail.


atavistic traits68
Atavistic traits
  • Such oddities are due to errors in development that cause ancestral traits normally suppressed in the genome to be expressed.
  • The presence of genes for such traits indicate an evolutionary history.
atavistic traits69
Atavistic traits
  • The embryos of a diverse array of vertebrates are very similar in early development.
  • Atavistic traits such as gill slits and a postanal tail, which are not present in the adult appear briefly before disappearing later in development.
other evidence for evolution jerry rigged structures
Other evidence for evolution: jerry-rigged structures
  • Jerry-rigged structures e.g. the Panda’s thumb.
  • In pandas, a wrist bone has been modified into a “thumb” that is used to grip bamboo stalks and assist in stripping leaves.
  • The “thumb” is not a very efficient solution to the problem of bamboo stripping.
panda s thumb
Panda’s Thumb
  • Natural selection must work with the material

available to it. Process is more like someone

tinkering in their workshop and assembling an

object from spare parts than an engineer building a

structure from scratch.

  • The jerry-rigged nature of the panda’s “thumb” implies pandas were not designed, but evolved.
other evidence for evolution adaptive radiation
Other evidence for evolution: adaptive radiation
  • Adaptive radiation and clusters of species.
  • Many remote islands are populated by morphologically diverse clusters of closely related species.
  • This pattern is difficult to explain without evolution.
process of adaptive radiation
Process of adaptive radiation
  • Ancestral colonists arrive on island.
  • Shortage of resident species means many niches are unfilled.
  • Ancestral colonizing species gives rise to many species that occupy unfilled niches.
adaptive radiation
Adaptive radiation
  • Examples: Darwin’s finches on Galapagos Island, Drosophila on Hawaiian Islands.
darwin s finches
Darwin’s Finches
  • On Galapagos Islands there are 13 species of anatomically very different, but closely related species of finch.
  • They differ greatly in beak size and diet having evolved very different lifestyles.
hawaiian drosophila
Hawaiian Drosophila
  • More than 25% of the world’s 1,250 species of Drosophila fruit flies found on Hawaiian Islands.
  • Few insect competitors so Drosophila have diversified to fill large number of niches.
if faunas were created why are there woodpecker finches but no woodpeckers on the galapagos islands
If faunas were created why are there woodpecker finches, but no woodpeckers on the Galapagos Islands?
artificial selection
Artificial Selection
  • Artificial Selection. Humans as the agents of selection have selectively bred for desirable traits in domestic animals and plants for thousands of years.
  • The tremendous diversity of body forms that have been produced in domestic dogs in very few generations show how quickly organisms can change in response to selection.
tameness in silver foxes
Tameness in silver foxes
  • One excellent example of artificial selection is Dimitri Belyaev’s work to breed tame Silver foxes.
  • In each generation he bred only from the tamest individuals and in only six generations was able to produce foxes that were eager for human contact and behaved like domestic dogs rather than foxes.
tameness in silver foxes86
Tameness in silver foxes
  • After about 30 generations 70-80% of the experimental population displayed extreme tameness.
  • In addition many foxes lots their fox-like look, became piebald and resembled Welsh collies. These were side-effects of selection for tameness (an example of pleiotropy: genes having more than one effect).

Silver fox after multiple generations of

selection for tameness (upper left)



creationism and intelligent design
Creationism and “Intelligent Design”
  • The idea of evolution has been harshly criticized by religious fundamentalists since the publication of the Origin in 1859.
  • This has been especially true in the U.S.
  • Repeatedly, believers in the literal truth of the Bible have attempted to have alternatives to evolution (i.e., creationism) taught in the public schools and to have the teaching of evolution either banned or restricted.
creationism and intelligent design89
Creationism and “Intelligent Design”
  • The U.S. Supreme Court has prohibited the teaching of creationism in public schools as a violation of the establishment of religion clause of the Constitution.
  • Latest attempt to insert creationism into schools is the idea of “Intelligent Design.”
creationism and intelligent design90
Creationism and “Intelligent Design”
  • The concept of “intelligent design” is outlined most clearly in Michael Behe’s book “Darwin’s Black Box.”
  • The central idea in “intelligent design” is that some structures in the body are so complex that they could not possibly have evolved by a gradual process of natural selection. These structures are said to “irreducibly complex.”
creationism and intelligent design91
Creationism and “Intelligent Design”
  • By “irreducibly complex” Behe means that a complex structure cannot be broken down into components that are themselves functional and that the structure must have come into existence in its complete form.
creationism and intelligent design92
Creationism and “Intelligent Design”
  • If structures are “irreducibly complex” Behe claims that they cannot have evolved. Thus, their existence implies they must have been created by a designer (i.e. God, although the designer is not explicitly referred to as such).
creationism and intelligent design93
Creationism and “Intelligent Design”
  • Behe’s main examples are various biochemical pathways in the body, the blood clotting system, and structures such as the bacterial flagellum.
creationism and intelligent design94
Creationism and “Intelligent Design”
  • Since the publication of Behe’s book, it has been demonstrated repeatedly that things he has claimed to be irreducibly complex are not in fact so.
  • E.g. the flagellum in eel sperm lacks several of the components found in other flagella, yet the flagellum functions well.
creationism and intelligent design95
Creationism and “Intelligent Design”
  • The blood clotting system in dolphins lacks at least one component that the human system has, yet it too is functional.
  • In addition, plausible gradual scenarios for the evolution of biochemical pathways including the Kreb’s cycle have been documented.
evolution of complex structures
Evolution of complex structures
  • The evolution of complex structures, such as the eye, appears difficult, but natural selection achieves this by the slow accumulation of minor improvements from one generation to the next.
evolution of complex structures97
Evolution of complex structures
  • Each step on the evolutionary pathway from a simple light sensing cell to a complex eye capable of focusing and producing color vision, must be beneficial to the organism that possess it and a slight improvement on earlier versions.
  • It is not necessary for a structure to be perfect or even very good, it just needs to be better than the alternatives to be favored by selection.

Variation in mollusc eyes from (a) pigment spot to (b) pigment cup to

(c) simple optic cup in abalone to (d) complex lensed eyes in a marine snail and


evolution of complex structures99
Evolution of complex structures
  • Computer simulations suggest that eyes can evolve easily and in nature eyes have evolved independently more than 40 times.