emp 1003 evolution

Evolution

Evolution

Antoine Vella

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There are innumerable varieties of lifeforms on Earth.

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How did the great diversity of life originate?Possible answer:All living things were created at the same time in their current form. Basis: traditional biblical interpretation.

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Possible answer: Different types of living things were created at different times. Basis: modified biblical interpretation

How did the great diversity of life originate?

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Possible answer:Different types of living things evolved from earlier types. Basis: science

How did the great diversity of life originate?

Evolution of whales

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This presentation consists of six sections:Evolution of Evolutionary ThoughtCharles DarwinThe Theory of EvolutionMechanisms of EvolutionTypes of EvolutionEvidence of Evolution

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Evolution of Evolutionary Thought

Section 1

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Early Evolutionary Thought - I

Anaximander (c.610 BCc. 546 BC) A Greek philosopher who thought that the universe was originally in a state of chaos from which came all creatures.Mankind sprung from some other species of animals, probably aquatic, through transmutations (i.e. changes). For this, some people consider him to be evolutionary theory's most ancient proponent.

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Early Evolutionary Thought - IIAristotle 384-322 BC The father of animal biology, he established basic principles of classification.He believed that organisms were created separately but developed from simple ones to others ever more complex: continuity of organization and unity of plan. He developed the idea of the Scala Naturae known also as the Great Chain of Being (see slides 10-12)

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Scala NaturaeThe Great Chain of Being or Scala Naturae is a classical and western conception of the order of the universe, whose chief characteristic is a strict hierarchical system.

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Scala Naturae

The idea was accepted by most educated men from Roman times until the Renaissance. It is composed of links, from the most base elements up to the very highest perfection: God.Perfection (God) Angels Humans Beasts Plants Rocks The concept of "animal, vegetable, and mineral" still survives and, importantly, made up the "three kingdoms" of Linnaeus's taxonomic system.

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Two illustrations of the Scala Naturae proposed by Aristotle, showing a passage from the simple to the complex and from the base to the sublime.

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Early Evolutionary Thought - II

Epicurus 341-270 BC Believed he world has endured for an infinite time and life developed without divine intervention. He formulated the beginnings of a theory of natural selection in evolution. e.g.: Many races of living things must have died out and been unable to beget and continue their breed. For, in the case of all things, either craft or courage or speed has from the beginning of its existence prohibited and preserved each particular race.

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Early Evolutionary Thought - IV

Pliny the Elder 23-79 AD A Roman scholar who was a Natural Philosopher and wrote Naturalis Historia, an encyclopedia of 37 books dealing with subjects like geography, biology, agriculture, anthropology, mineralogy and other topics. He described in detail what today would be called biodiversity.

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Early Evolutionary Thought - VMatthew Hale (1609- 1676) was an English judge and writer who is credited with having coined the word evolution.

The word comes from the Latin word "evolutio", meaning to "unroll like a scroll".

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Early Evolutionary Thought - V

Ironically, Hale coined the word evolution in a book he wrote in 1677 to deny its existence and to attack what he called the atheist ideas of Epicurus and other classical Greek thinkers. (slide 13)

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Challenges to Established Views

With time however, there were some facts which came to light and which seemed to challenge the idea of a world that was unchanging since Creation. One of these was the discovery of fossils.

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Challenges to Established Views

It seemed obvious that there existed animals which were different from those inhabiting the known world. For a long time, these vaguely reptilian fossils were explained as the remains of dragons and other mythological creatures.

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Fossils and DragonsDinosaur fossils had been known for centuries as "dragon bones" or the remains of giants.

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Mammoths and CyclopsElephant and mammoth skulls had also been thought to belong to a race of one-eyed giants which, supposedly still existed, since even the concept of extinction was not accepted widely.

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Fossils and DragonsIt wasn't until Dean William Buckland of Oxford, described the carnivorous "lizard" Megalosaurus (in 1824) that dragons were formally studied as an extinct group of giant reptiles.

MegalosaurusDean William Buckland1784 - 1856

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MegalosaurusEven though Bucklands reconstruction was incorrect he still has the great merit of discovering dinosaurs.

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Early Evolutionary Thought - VI

Georges-Louis Leclerc, Comte de Buffon (1707- 1788)

A French naturalist who influenced the next two generations of naturalists, including Lamarck, Wallace and Darwin, among others.(see slides 32 43)

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His Histoire naturelle, gnrale et particulire (36 volumes) included everything known about the natural world.

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Buffon considered the similarities between humans and apes, and the possibility of a common ancestry.

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Early Evolutionary Thought - VIBuffon observed that some animals retain parts that are vestigial and no longer useful, suggesting that they had evolved

rather than been created individually or generated spontaneously

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Early Evolutionary Thought VIIRev. Thomas Robert Malthus (1766 - 1834) Malthus was not a naturalist but an economist who was interested in the way that human populations regulated themselves. He is included here because his ideas had a great influence on the development of evolutionary thought.

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Early Evolutionary Thought VIIHe was responsible for the concept of the struggle for survival, or natural selection, upon which theories of biologists* later depended.

* including those of Spencer, Darwin and Wallace

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Pre-Darwin Naturalists - IGeorges Cuvier (1769-1832) proposed the concept of what later became known as Catastrophism, (the term itself was coined later) which suggested the occurrence of many violent supernatural catastrophes that had occurred on earth since its creation.

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Each catastrophic event had wiped the earth clean of many living creatures.The survivors of these events then continued on - perhaps with the aid of newly created animal species.

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CatastrophismAlthough this theory is now known to be incorrect, Cuvier has the merit of being one of the first to state that species can become extinct.

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Pre-Darwin Naturalists - IIJean-Baptiste Lamarck (1744 - 1829) a French naturalist, one of the first to use the term biology in its modern sense. He was an early proponent of the idea that evolution occurred and proceeded in accordance with natural laws.

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Pre-Darwin Naturalists - IILamarck believed in spontaneous generation, with the simple organisms thus created changing over time and becoming gradually more complex and closer to perfection as they evolved.

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Pre-Darwin Naturalists - IILamarck is remembered today mainly in connection with a discredited theory of heredity, the "inheritance of acquired traits".

This theory states that if an organism changes its shape during its lifetime (i.e. acquires new characteristics), these changes will be carried on to future generations.

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LamarckismLamarck developed two laws:Frequent use of any body structure strengthens, and enlarges that structure while its permanent disuse weakens it until it finally disappears.

All changes acquired during the lifetime of an organism are passed on to the offspring.

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LamarckismSummary of Lamarck's evolutionary theory: Organisms progress towards higher formsDevelopment follows desire or will use/disuse

This leads to replacement or extinction of organsAcquired characteristics are passed on to offspring. Parallel evolutionary chains are possible

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Lamarcks ConceptEarly giraffes had short necks that they stretched for foodThe longer necks were passed on to their offspring, who then stretched them moreEventually only long-necked giraffes existed

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Alfred WallaceWallace was an Englishman who came from a family of modest means. He received a limited education, worked many jobs: construction, surveying, assistant, watchmaker, teacher, and othersAlfred R. Wallace1823 - 1913

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Alfred WallaceWallace loved natural history and the outdoors. He travelled to Brazil with Henry Bates, another naturalist, and explored the Amazon.During this voyage he collected and sold large numbers of biological specimens, especially insects.Alfred R. Wallace1823 - 1913

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Wallaces Expeditions1848: Wallace and Bates sailed for South America and gathered large collections of specimens.

Artists impression of Henry Bates exploring the Amazon

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Wallaces Intuition1854: Wallace studied the fauna of the Malay Archipelago and realised that the area was divided biologically by a narrow strait, separating Asian from Australasian fauna.

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Wallaces IntuitionThis boundary is still known as Wallace's Line.It lies just east of Borneo, marking the boundary between the Asian and the Australasian faunas.

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Wallace applied the geological idea of Uniformitarianism to biology. This is the idea that the natural processes that have operated in the past are the same that operate today and apply everywhere in the universeBasis for Wallaces Theory

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UniformitarianismThe term was coined in 1832 by William Whewell who also coined the term Catastrophism to define the religious idea that life on Earth was periodically subjected to catastrophes and re-created every time.

The idea had actually been conceived first by James Hutton (right), a Scottish geologist, in the late 18th century.

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Charles Lyellwho supported Huttons idea that the earth was shaped by slow-moving forces still in operation today.

Lyell was a geologist

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Uniformitarianism implies that layers of silt and sandBasis for Wallaces Theory

are laid down slowly and uniformly over long periods of time.These layers cover dead creatures slowly turning them into fossils.

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This gave an idea how fossils were formed and showed how organisms developed through time.Basis for Wallaces Theory

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As sediments are laid down chronologically, theBasis for Wallaces Theory

fossils found in lower layers are older than those found in layers above them.

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Wallaces Natural SelectionWallace also realised that the classification chart of a species might look more like a tree than a straight line. No species came into existence unless it was derived from another similar one that was its predecessor.

The tree of human evolution according to the biologist Haeckel (1891)

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Wallaces publicationIn 1855, Wallace anonymously wrote a paper, On the Law Which Has Regulated the Introduction of New Species,arguing that some kind of evolution of species must have occurred and searching for a mechanism (the same thing that Darwin was saying).

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Wallaces InspirationIn this he was inspired by the work of Malthus, a British economist. In An Essay on The Principle of Population (1797), Malthus had observed that most organisms produced far more offspring than could possibly survive.

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Theory of MalthusWhen resources are plentiful, the size of a population tends to increase until it outstrips its food supply. This led Malthus to believe that poverty, disease, and famine were a phenomenon of nature, leading to a "struggle for existence".

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Charles Darwinand the Theory of EvolutionSection 2

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Charles DarwinBorn in England, son of a wealthy doctor, he studied medicine but dropped out, then tried theology, but was much more interested in natural history.

Charles Darwin(1809-1882)

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After university, Darwin signed on as unpaid naturalist on the Royal Navy ship Beagle and took a 5-year trip around the world (1831-1836).

H.M.S. Beagle

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Voyage of the HMS BeagleThe ships mission was to map the coast of South America, but it travelled around the world, including the Galapagos Islands, of volcanic (hence recent) origin off the coast of Ecuador.

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Darwin was struck by the diversity of animals on the Galpagos Islands.He thought of adaptation to the environment and the origin of new species as closely related processes. As populations, separated by a geographic

barriers, adapted to local environments, they became separate species.

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Darwins ObservationsDuring the voyage Darwin noted many things that suggested evolution must have taken place. These observations, taken together, suggested that species change over time, i.e. evolution occurs.

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What Darwin Observed - ISouth American fossils resembled living animals.

Glyptodont (2000 kgs) is a fossil mammal that looked like the modern day armadillo (2 kgs)

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What Darwin Observed - IIParts of the world with similar climates (e.g. South America, Australia) have very different organisms. It did not seem to make sense if the organisms were created.Why create different animals for similar climates?

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Similar but DifferentTwo dog-like medium-sized predators filling the same ecological niche: a marsupial (left) and a placental (right).

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What Darwin Observed - IIIMeanwhile certain plants and animals on each continent are different and distinctive and found only there.

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What Darwin Observed - IVMany species on oceanic islands are found only there (endemic). Often groups of very similar species are found on these islands. e.g. Galapagos iguanas and finches.

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The Galapagos FinchesOn 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.

#64Each of these finches is adapted to gathering and eating a different type of food. Tree finches have beaks largely adapted to eating insects and, at times, plants. The woodpecker-type finch, a tool-user, uses a cactus spine or twig to probe in bark of a tree for insects. Ground finches have beaks adapted to eating prickly-pear cactus or different-sized seeds.

Galapagos FinchesDarwin asked himself why there was such tremendous diversity among these small birds.Why did they have physical similarities to the mainland species but had many more forms?

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Galapagos FinchesDarwin concluded that these island birds had originated from the same species but had then adapted themselves to living in different habitats.

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The Origin of the FinchesSome 10,000 years ago a number of small finches, probably grassquits, made their way from South America to the Galapagos Islands. The small birds happened across a landscape relatively free of competitors. The isolated location of the islands meant that new species arrived relatively infrequently.

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Adaptation of the FinchesGeographically isolated and without competition from similar species, these finches developed distinctive

anatomy (particularly beak size and shape) and behaviour, with each species exploiting a unique feeding niche.

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Adaptation of the FinchesBills are adapted in different species for different purposes, such as crushing seeds, pecking wood, and probing flowers for nectar.

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The Galapagos Finches

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Darwins Finches

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The woodpecker finchThis Galapagos finch is one of the few birds in the world to use tools when feeding, in this case a twig or cactus spine. It uses cactus spines or twigs to pry insects & larvae from cacti or from beneath bark.

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Artificial SelectionBesides the voyage on the Beagle and the observations made, another issue influenced Darwin: Artificial Selection.

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Artificial SelectionDarwin studied pigeon-breeding and realised that the domestic types of pigeon, which were all derived from the wild species, had different body forms because the breeders had selected particular birds to produce offspring.

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Natural SelectionDarwin imagined a process similar to artificial selection but carried out by nature and producing the wild organisms we see today. He called it Natural Selection.Darwins idea was based on some preliminary generalisations, made after he observed plants and animals both during his Beagle voyage and in England itself.

Tree trunks grew darker with soot from pollution. Therefore, the light-coloured moths were more visible to predators, and since they were more easily caught, their numbers declined. The numbers of dark moths, however, increased. When pollution decreased, the opposite happened.

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Natural Selection: 4 assumptionsDarwins generalisations (today accepted as true) are:

Individuals in species vary (random genetic differences)Some of these variations are passed on (hereditable)More offspring are produced that can survive each generation (struggle for existence)Survival and reproduction are not random (the favourable variants are naturally selected)

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The Origin of SpeciesWhen Darwin returned home he worked for many years analysing his data.

In 1844 he wrote a long essay on the origin of species and natural selection but did not publish it immediately because he was wary of the reaction it would provoke.

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The Origin of SpeciesIn June 1858 Darwin received a manuscript from Alfred Wallace who had developed a theory of natural selection similar to his own.Darwin quickly finished his own book and published it the next year.

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On the Origin of Species by Means of Natural Selection (1859) became one of the most influential scientific texts of all times.

(The entire printing of 2500 copies was sold that same day!)

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Other PublicationsAfter Origin of Species Darwin published various other books including one to show the variations that existed among domestic plants and livestock.

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The Theory of EvolutionSection 3

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After Darwin observed plants and animals both during his voyage on the Beagle and in England itself he reached certain conclusions (general assumptions) which are today accepted as true.Theory of Evolution

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There is variation in populations. This variation is heritable.In every generation some organisms are more successful at surviving and reproducing than others.Finally, survival and reproduction are not random, but related to the variations among individuals. Organisms with the best characteristics are selected by nature.

Darwins Assumptions

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This is the logical result of four features of all living systems: Variation Inheritance SelectionTimeNatural Selection

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VariationIndividuals in any population vary from one another.

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InheritanceParents pass on their traits to their offspring genetically.

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SelectionSome variants manage to reproduce more than others.

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TimeSuccessful variations accumulate over many generations.

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Basic AssumptionsIn a population individuals vary from each other have different characters.These different characters are passed on from parents to offspring.Because of these inherited characters, certain individuals are more successful at surviving and reproducing than others.In time, this will influence and determine the characters of the whole population.

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The TheoryThese points, taken together are basicallywhat evolution is all about: descent with change.Important: Individuals do not evolve, only populations do.

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Mechanisms of EvolutionSection 4

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As explained in the previous section, evolution is a process by which populations change over time.How does this come about?

Evolution of the camel

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Impetus for ChangeAs Darwin theorised, the main stimulus to change is a process known as Natural Selection. We might consider it the motor, the energy, which drives evolution.

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Natural SelectionWe have already seen how Natural Selection works: organisms belonging to the same population are different from each other and the environment selects the ones which are better suited.

The tail spines give this stegosaurus a better chance to survive an attack by a predator.

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AdaptationOrganisms that are best suited to their environment as said to be adapted and the process known as adaptation.

Flightless Birds

Adapted to running

Adapted to swimming

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Adaptation

Among the animals seen by Darwin at the Galapagos were cormorants which had lost the power of flight.

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AdaptationThey had no predators from whom they had to escape by flying and, at the same time, the stubby wings gave them an advantage as it made them better swimmers (like penguins).

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AdaptationDarwin saw the transformation of wings into flippers as a case of adaptation to a particular environment.

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Lamarck and DarwinThe idea that the environment, or nature as they called it in the 19th century, has an effect on evolution was also proposed by Lamarck but he had a different mechanism in mind.

According to LamarckAccording to Darwin

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Darwins Natural SelectionEarly giraffes had necks of various lengths.Natural selection due to competition led to survival of the longer-necked animals and their offspring.Eventually only long-necked giraffes survived the competition.

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Lamarck and Darwins Views

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Basis for SelectionWe have seen that nature selects certain individuals who survive and reproduce instead of others.

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Survival of the FittestThis is a phrase which refers to the competition for survival or dominance.Although it is now used especially for evolution, it was originally applied to socio-economics by philosopher Herbert Spencer who, in 1864, drew parallels with Charles Darwin's theories about natural selection.

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Survival of the fittestThe phrase is often felt to be unhelpful - biologists almost exclusively use natural selection instead. The term fitness is a subjective one, i.e. there is no way to measure fitness.

If it is measured in terms of survival, the phrase becomes survival of the survivors which doesnt make sense.

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Unethical Use of ConceptIn early Victorian times, the concept of survival of the fittest was used to justify social inequality and the great disparity between classes.

The 1850s and 1860s were the decades when Charles Dickens was writing and his novels describe the social injustice that existed at the time.Charles Dickens 1812 - 1870

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A weak point of Darwins theory was that nobody knew exactly how different characters came into being because genetics hadnt yet been developed as a science..

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How variants come to beToday we know that the main factors which bring about variants are: MutationsGenetic DriftGene flow

There are some other ways (e.g. so-called gene hitchhiking) that will be discussed as part of genetics.

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MutationsThese are random changes in the DNA. A single mutation can sometimes have a large effect, but usually, evolution depends on the accumulation of several mutations.

Left mutated whippet - increase of muscle mass and twice the size of normal whippet (right)

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Most mutations are harmful (even lethal) or of no significance but sometimes they give an organism the edge when competing against other individuals

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Not all morphological changes are due to mutations; they may also have environmental causes.

Cold temperatures during the embryonic stage caused this doubling of the front legs of this mite.

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Gene DriftThis is the random change of gene frequency between one generation and the next, due to the random of gene distribution uring reproduction.

The ratio of brown to green marbles drifts around (5:5, 6:4, 7:3, 4:6 . . .)

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Gene DriftThis is different from classical natural selection because it is random while natural selection is essentially non-random.

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Gene FlowThis is the transfer of genes from one population to another through interbreeding. If it occurs between species it is better known as gene transfer.

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Types of Evolution

Section 5

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After Darwin, many scientists contributed to understand better the process of evolution and, as new information is acquired, different facets begin to emerge.

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Micro- and MacroevolutionMicroevolutionChanges in gene frequency in a population that give rise to relatively small modifications over a short period of time.

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Macro- and MicroevolutionMacroevolution The descent of different species from a common ancestor over many generations.

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Macro- and MicroevolutionMacroevolution on the left-hand panel shows the development of new species.

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Macro- and MicroevolutionMicroevolution on the right shows changes undergone by a single ancestral species to give rise to closely related ones.

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Convergent EvolutionThis occurs when two distinct species with differing ancestries evolve to display similar physical features.

Dolphin (mammal), ichthyosaur (reptile), swordfish (fish) and penguin (bird) all show a similar shape (morphology) because they all live in the sea.

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Convergent Evolution

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AnalogyThis is said of an organ or structure that appears similar in unrelated organisms.

All animals which fly have wings which are superficially similar, even though the animals themselves are unrelated.

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Convergent Parallel EvolutionThis occurs when two independent species evolve together at the same time in the same eco-space and acquire similar characters.

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Convergent Relay evolutionNon-related species acquire similar characteristics through in similar ecosystems but at different times e.g. the dorsal fins of ichthyosaurs and sharks.

The ichthyosaur (top) is a reptile, the shark (left) a fish but the two animals are similar body shapes.

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Divergent EvolutionThis is when related species evolve different traits. The accumulation of such differences can eventually lead to the formation of new species.

Creation of botanical variants of Brassica oleracea. In this case the different types are not species but varieties.

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Divergent Evolution

Common ancestor of snakes

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HomologyThis is when the same organ or structure takes on a different shape in different organisms. This is considered one of the main pieces of evidence in favour of evolution.

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Homologous Bones

The skeleton of the upper limb in different mammals shows the same bones, though modified in shape.

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Disruptive EvolutionThis refers to changes in which two opposing characters are both favoured over the others and the population is divided into two distinct groups.

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Stabilizing SelectionIn this process, diversity decreases as new characters are not beneficial and die out. The population is thus stable and does not undergo changes.

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Directional SelectionThis happens when a single set of characters is favoured over all others so that the population as a whole undergoes change.

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Co-evolutionThis is when two or more species inluence the evolution of each other. E.g. The evolution of a parasite and its host or that of flying insects and flowering plants.

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Evidence for EvolutionSection 6

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Proof of EvolutionThere is a very large amount of information and scientific fact to prove that evolution has and is still occurring. Moreover such evidence also shows us how takes evolution place.

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Proof of EvolutionAll the evidence available may be grouped in these five sections:Evidence from palaeontology Evidence from comparative anatomy Evidence from comparative embryology Evidence from geographical distributionEvidence from comparative physiology and biochemistry

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Palaeontology The study of past life based on fossil records and their relations to different geological time and layers provides us with information on the evolutionary history of life on Earth.

Fossil records Development of species Living fossils

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Fossil RecordsFossils show us what kind of organisms were alive hundreds of thousands or millions of years ago.

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The number and complexity of different fossils at different rock levels show that:Older fossil-bearing rocks contain fewer types of fossilized organisms and they all have a more simple structure. Younger rocks contain a greater variety of fossils with structures which are increasingly complex.

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Fossil recordsSedimentary rock is made up of a series of horizontal layers or strata, each containing fossils typical for that time period when they were laid down.

The lowest strata, i.e. the oldest rocks, have the earliest fossils while higher strata contain younger rocks with more recent fossils.

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Fossil Stratification

A succession of organisms can be seen from fossils which supports a theory of progressive increase in complexity of these organisms.

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Sedimentary rocks, such as fossil-bearing limestone, can also help geologists determine geologic time. Because the bottom layers were deposited

first, the oldest fossils are found there.

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The accumulation of shells or other fossils in limestone provides us with a record of the organisms that used to live in the ancient oceans. Fossil from Gozo

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Maltese fossilOne of the first fossils ever described in scientific literature had been discovered in Malta. In 1670, Agostino Scilla illustrated three teeth in a fossil whale jaw from Malta.

It represents the species Squalodon melitensis, a shark-like whale.

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Maltese fossilScilla's illustration, (top,) shows three molar teeth with triangular crowns with many small projecting denticles. Each tooth has two roots. The fossil is still in existence in the Sedgwick Museum at Cambridge (bottom)

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Fossil recordsIt is possible to find out how a particular group of organisms evolved by arranging its fossil records in a geological sequence.

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Fossil recordsSuch a sequence can be worked out because fossils are mainly found in sedimentary rock.

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Directional selection

#152Directional selection occurs when natural selection favors one extreme phenotype (see arrows), resulting in a shift in the distribution curve. Equus, the modern-day horse, which is adapted to a grassland habitat, evolved from Hyracotherium, which was adapted to a forest habitat.

#153Table 27.3 (page 561) gives detailed information about the differences between the three domains.

The Evolution of HorsesA particularly well-documented case of evolution within a group.

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But, the standard diagram of the previous slide does does not clearly show transitional stages whereby the four-toed foot of Hyracotherium, otherwise known as Eohippus, became the single-toed foot of Equus. Fossils show that the transitional forms predicted by evolution did indeed exist.

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Information from Fossils

The teeth of extinct animals allow us to find out what they were eating and how they lived.

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Comparative AnatomyComparing the anatomy of groups of organisms reveals that certain structural features are basically similar.

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Comparative AnatomyThe basic structure of all flowers consists of the same parts but the size,

colour, number and shape of each part are different for each individual species

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Comparative AnatomyWhen widely separated groups of organisms originate from a common ancestry, they are expected to have certain basic features incommon. The degree of resemblance between organisms should indicate how closely related they are in evolution.

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Comparative Anatomy

A giraffe (left) and goat (right) both have cloven even-numbered hooves, showing they are related.

A rhino (left) and horse (right) both have hooves with an odd number (3 and 1) showing they are related.

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Comparative AnatomyDo the stripes on a tiger and a zebra indicate that the two animals are related?

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In comparative anatomy we have to consider the following aspects:Homologous structuresAnalogous structuresVestigial organs

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Homologous structuresForelimbs of mammals have the same bones but modified for different uses. It would make no sense if the organisms were specially created, but is logical if they share a common ancestor.

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Comparative Anatomy

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Homologous structures having common origin. Even though the forelimbs have evolved to carry out different tasks they are all constructed from the same bones.

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Analogous StructuresUnder similar environmental conditions, different structures in different groups of organisms may undergo changes to serve similar functions. This phenomenon is called convergent evolution.

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The dorsal fin of a shark has a different origin to that of a dolphin.

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Analogous StructuresSimilar structures in organisms apparently bearing no close phylogenetic links but showing similar adaptions to perform similar functions are described as analogous.

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Convergent EvolutionThis happens when organisms which are not related but which live in similar habitats eventually acquire similar structures and morphology. It is the origin of analogous structures

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Vestigial organsOrgans that are smaller and simpler in structure than corresponding parts in the ancestral species are called vestigial organs. They are usually degenerated or underdeveloped.

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Vestigial organsThese can be explained by changes in the modes of life or environment of the species. They are thought to have been functional in the ancestral species but have now become unnecessary and non-functional.

Vestigial limbs in whale (left) and snake (right)

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All organisms contain some vestigial structures that give clues to the past.

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Vestigial Structures in Humans

Wisdomteeth

AppendixTailbone

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Hind limbs in whales

Whale embryoModern whaleFossil whale

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Vestigial organs in humans

AppendixNictating membrane in eye

Arrector pili muscle at base of hair follicles makes hair stand up.

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Embryology

Embryos of many vertebrates are very similar during early development, suggesting common descent.

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Comparative EmbryologyFor example, adult vertebrates are diverse, yet their embryos are quite similar at very early stages. Fishlike structures still form in early embryos of reptiles, birds, and mammals. In fish embryos, a two-chambered heart, some veins, and parts of arteries develop and persist in adult fishes. The same structures form early in human embryos but do not persist as such in adults.

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Comparative EmbryologyComparative embryology shows how embryos startoff looking the same. As they develop, their similarities slowly decrease until they take the form of their particular class.Homologous structures in adults develop from homologous groups of cells in embryos: they share developmental pathways.

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Geographical DistributionBiologists have discovered many puzzling facts about the presence of certain species on various continents and islands (biogeography).

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Geographical DistributionIt is not only living animals; fossils are also distributed geographically in ways that indicate that evolution has taken place. The same kinds of fossils are found from areas known to be adjacent to one another in the past but which, through the process of continental drift, are now in widely divergent geographic locations.

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For example, fossils of the same types of ancient amphibians, arthropods and ferns are found in South America, Africa, India, Australia and Antarctica, which can be dated to the Paleozoic Era, at which time these regions were united as a single landmass called Gondwana.

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Continental DriftSometimes the descendants of these organisms can be identified and show unmistakable similarity to each other, even though they now inhabit very different regions and climates.

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Continental Drift

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Continental Drift

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Continental Drift

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Continental Drift

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Continental Drift

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Continental Drift

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Migration and IsolationMap showing distribution of present members of the camel family (in blue)

Solid black lines indicate possible migration routes

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Migration and isolationFossil records show that evolution of camels started in N. America, from where they migrated to S. America and Asia and then Africa.

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Migration and IsolationOnce each population was isolated it evolved along different lines, giving the modern camel in Asia and Africa and llama in South America

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ChromosomesIn all organisms, genetic hereditary information is passed from one geration to the next through avery long complex molecule called DNA. Strands of DNA make up structures called chromosomes.

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ChromosomesThe DNA strand making up the chromosome is subdivided into sections called genes which

determine the characters of the organism.

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ChromosomesAmong the building blocks of DNA are smaller molecules (amino-acids) known as bases . There are only four bases and they are found in all organisms, from bacteria to humans

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DNA EvidenceDarwin predicted that humans and primates would be found to be closely related. Today we can test this hypothesis: humans and chimpanzees share 98% of the DNA.The DNA of nonhuman primate species is remarkably similar to those found in human DNA.

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BiochemistryApart from DNA, there are many other molecules which are shared by different organisms. Sometimes these molecules are identical and, at other times, they are slightly different.Both similarities and differences can be used to prove that organisms share a common ancestor.A model of a protein molecule.

#BiochemistryAn example is the variance of the protein known as Cytochrome c. This protein has undergone mutations and is slightly different in different species. By looking at the differences between variants of the same protein therefore, it is possible to count how many mutations have occurred. (see example on next slide)

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Comparative BiochemistryThe protein known as cytochrome c of humans and monkeys is different only because of one single

mutation that is generally accepted to have occurred4 million years ago.

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Molecular Vestigial TraitsBesides visible organs which have become vestigial, humans also possess genes which are no

longer functional but similar genes are still active in other animals. It is thought that such non-functional genes are vestiges.

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emp 1003 evolution

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