Chapter 15: Darwin's Theory of Evolution

Chapter 15: Darwin's Theory of Evolution

Chapters 16 - 17: Darwins Theory of Evolution & Population Genetics Human, Chimp, Gorilla, Orangutan What is Evolution? Evolution is the gradual change in a species over time. Modern organisms have descended from ancient organisms History of Charles Darwin

Born: 2/12/1809 1882 Very wealthy (moms side were Wedgewoods) Married 1st cousin Studied medicine & theology but ended up being a naturalist. Took a 5 year voyage on the HMS Beagle in 1831 (England to SA), around SAs Cape Horn to the Galapagos Islands, below Australia and the Cape of Good Horn, back to SA and then to England) Darwins grave in Westminster Abbey, London The Beagle's Voyage

Galapagos Is December 1831 - expedition leaves Plymouth Crosses the Bay of Biscay and meets rough seas Darwin is seasick Unable to land at Madeira as the tides are against them Unable to land at Tenerife as the islanders fear that disease has been carried from Britain Crosses the Atlantic Ocean to Brazil, via the Cap Verde Islands and the equator February 1832 - lands at Bahia (Salvador) in Brazil, where Darwin collects botanical specimens and comes across slavery for the first time On to Rio de Janeiro where Darwin spends two months making observations. He collects 68 beetles

in one day! Next stop - Tierra del Fuego, and three natives and a Christian missionary are left behind to work with the islanders On to the Falkland Islands where Darwin observes very simple tiny plant-like sea creatures June 1834 - the Beagle sails round the southern point of South America, in the stormy seas of the Straits of Magellan On to the island of Chiloe and the Chonos group of islands, where Darwin observes active volcanoes February 1835 - at Valdivia, Darwin experiences an earthquake, and visits nearby Concepcion where he finds the town almost destroyed by the

earthquake September 1835 - the Beagle arrives at the Galapagos Islands, where Darwin collects some of his most important specimens, the finches which can only be found on these islands January 1836 - the expedition reaches Australia April 1836 - Darwin observes an atoll, a coral reef around a lagoon, in the Keeling and Cocos Islands The expedition goes round the southern tip of Africa, via the stormy Cape of Good Hope, and crosses the Atlantic to complete work in Brazil October 1836 - the Beagle arrives back at Falmouth and Darwin is reunited with his family The Galapagos Islands

1000km west of S. America Volcanic chain of Islands Low islands were hot, dry & basically void of life. Higher elevations islands had > rainfall & therefore more variety of life Unique land tortoises & marine iguana. Species differed from island to island, especially the tortoise shells & the little brown birds later determined to be finches Darwin was extremely seasick throughout the

voyage! Contracted Chagas disease (protozoan) Published book: On the Origin of Species in 1858 What got Darwin questioning the modern day concepts? Collected plant and animal specimens on his voyage. Made numerous notes & drawings Noticed a pattern of diversity amongst organisms observed 68 different beetle species/day in Brazilian forest Found flightless rhea in grasslands of S.

America and ostriches in Africa. In Australia, there were emus in the grasslands. See anything in common? Collected fossils and noticed that they resembled organisms alive today & others totally different than of those today. Darwin notices that different, related species occupying similar habitat tended to look more similar or have many physical traits in common. Emu, ostrich and rhea He also noticed that related species occupying different habitats took on physical traits that seemed to make them fit in better with the habitat.

Tortoises He could even tell which island the species came from by their shells. Galapagos Tortoises Isabela Tortoise Eats vegetation close to the ground Hood Island Tortoise Vegetation is all up higher and sparse. Does this look like anything from today?

Archaeopteryx Do these resemble anything alive today? Darwin takes notice of this Could these all have come from one common ancestor and changed to fit into the particular environment of the island? Ideas that Shaped Darwins Thinking Hutton and Lyell Geologist who felt that the earth was millions of yrs old (actually 4.6 billion) & that the earth has changed over its history to its present

form Earth is in layers that formed very slowly & has been altered over time by forces of nature. Using Lyells Principles of Geology: Felt that if the earth could change, so could its living inhabitants It would take a very long time for organisms to change & since the earth is millions of years old (according to the time), there was plenty of time for this change The earth is actually ~ 4.6 billion years old

Pages from Darwins journals Jean Baptiste de Lamarck (1801) Believe in decent from common ancestry Proposed that through selective use and disuse of organs, organisms acquired or lost certain traits during their lifetime. By passing on these acquired traits to their offspring, a species can change over time. Lamarcks theory 1. Tendency towards perfection

Always changing to help them live more successfully. Desire to change The giraffes had eaten all the food on the lower branches & needed to get to the food up higher. The giraffe got its long neck by stretching it to get to the higher up leaves. 2. Use and Disuse Organisms can alter their shape or size by using their body in new ways. Stretch that neck and those legs giraffes! 3. Inheritance of Acquired traits traits in an organisms lifetime could be passed onto their offspring.

Those giraffes that stretched their necks and lengthened their legs will have offspring with long necks and legs Thomas Malthus (1798) Reproduction rate is faster than death rate. Population growth is an exponential growth. Sooner or later, there will not be enough food or space War, famine & disease are the only forces to keep the population size from outdistancing food supply If organisms produce far more offspring than can survive, what factors determine which ones survive and reproduce?

Point of Crisis Resources Increase in food supply is arithmetic while population increase in exponential. Crisis occurs when the population outdistances the available resources Fossil Evidence Fossil evidence shows that living things have been evolving

on earth for millions of years. Also showed that the geographic distribution of organisms lines up with the movement of the earths crusts & that newer (more modern) forms of fossilized organisms are found in the upper layers of rock Homologous Structures Structures that have similar form but different functions Bones of our

forearm, the front flipper of a whale, the wing of a bat & legs of a turtle. Could all four limbed animals with backbones have descended with modification from a Analogous Structures have same common ancestors? ancestors function but different structure. Occupies same niche (butterfly and bat wings)

What about structures that are no longer in use? Vestigial organs Structures which no longer have a function to the organism. Our appendix, hair, coccyx, wisdom teeth These vestiges had a useful function at one time but since they are no longer of an adaptive use to the oganisms, they have become reduced with time. Embryological & Biochemical Evidence Not used by Darwin but in use today! 1. Early stages of development of many

animals with backbones are very similar Children of Evolution video 2. Using modern biotechnology, examine the biochemicals, genes & DNA of organisms. Similar organisms will have more in common. The more closely related they are, the more recently they descended from a common ancestor Amino Acid Sequencing evidence Darwin Puts it all Together!! Darwins Theory of Evolution ***22 years after Beagle voyage, writes On the Origin of Species

1. Natural Variations Inherited variations/adaptations exists between organisms w/I a population 2. Malthusian Doctrine Organisms in nature produce more offspring than can survive 3. Competition for limited resources among members of a species 4. Struggle for existence Due to natural variations, there exists advantages & disadvantages among members of a species

5. Survival of the fittest & Natural Selection Those members of the population w/ the best natural variations (adaptations), will survive & pass these traits onto their offspring. Those without the variations will not survive Fitness is measured in the # of grandchildren one has Nature selects which variations are the best suited to the environment. 6. Species change over time Due to natural selection. New forms arise & other disappear Also known a Differential Reproduction Natural Selection

There is variation in traits There is natural selection. Some are selected out, some arent There is heredity. Survivors reproduce End result. Possible speciation Peppered Moth Simu lation 7. Common Descent Species alive today descended with modifications from past species

No one ever said that we were monkeys though. We primates descended from a common ancestors 8. Adaptive radiation Darwins Finches small brown birds Occurs when a species or group of species evolves into many new species to fit into a particular niche. Reduces competition and increases survival Adaptive radiation Some evolved a shorter, fat beak for cracking large seeds, some have a smaller, pointier beak for opening small seed, while others have a long

pointed beak for getting into creases in bark for insects Fill open niches depending on your particular adaptation. If everyone does the same thing, there will be too much competition and only the fittest will survive Adaptive Radiation Darwins Finches illustration Natural Selection Lab Gene pool All the genes from a single population combined together

50:50 with our lab Relative gene frequency Number of times a particular allele occurs in the gene pool. 0.5: 0.5 at start of lab Changed through generations Small Lima bean gene frequency increased Large Lima bean gene frequency decreased If you continued this lab through other generations, what do you think would have happened to the gene frequencies? Small Lima beans gene frequency would continue to go up while the large

beans would decrease over time. Eventually, there wouldnt be many large beans so the small limas would be easier to pick off (thats all there is now). The gene frequencies would then change again. If all the larges though were picked out, they would become extinct Natural Selection Lab Generation 1

2 3 4 5 6 Total number of Beans in Bag 100 100

100 100 100 100 Total number of Small Lima beans 50 Total number of Large Lima beans

50 Number of Small Lima beans removed Number of Small Lima beans remaining Number of Large Lima beans removed Number of Large Lima beans remaining Total number of beans remaining in bag Frequency of Small Lima beans remaining in bag Frequency of Large Lima beans remaining in bag

1.0 Key: ___ = Small Lima ___ = Large Lima . 5 0 1 2

3 4 5 6 Divergent Evolution lecture

Two or more related populations become more and more dissimilar. (as seen in homologous structures) Darwins finches, iguana & tortoises Results in speciation formation of a new species Adaptive radiation

What very important information was Darwin missing in his theory of evolution in 1836? 1. What was the source of variation? Mendels work not published until 1900 2. How are these variations passed form generation to generation? 1910 Scientists combined the two mens concepts. Today, a combination of genetics, molecular biology & evolutionary theory work together to explain variations & natural selection

Sources of Genetic Variation 1. Mutation may increase, decrease or no effect on the organisms fitness 2. Gene shuffling luck of the draw. During meiosis & fertilization, genes get shuffled, much like cards in a deck (Genetic recombination) 3. Crossing over new combinations result during prophase I of meiosis 4. Sexual Reproduction 1. Provides new genes w/ each fertilization 2. This does not change the gene frequency though

Among the Amish population, polydactylism is very common. Why? Is it a favorable trait for working on farms & doing more hand work? Animation Genetic Drift Sicilian family In a small population (isolated one), a particular allele may occur more frequently even though it doesnt lead to the fitness of the population, it is just there An Australian Aboriginal cave painting Founder Effect

Is the change in gene frequency as a result of the movement of a small group of a population. Think of any small island and their populations. If only 4 of you were to be isolated on a deserted island, how might your descendants be different from the general population of the world? Bad luck for the reds & where are the yellows?!!

Some sorter didnt do their job!! Genetic Drift Cut open the bag and take out 3 M & Ms. These represent the organisms that left the general population. How does the new population differ from the main population? Now that you are isolated, over time, if left alone, what may happen to the members of your species on that island? Isolating Mechanisms causing Speciation

Ruffed grouse (formation of a new species) courtship dance, mating drumming atFiddler crabs 1. Behavioral & Temporal (reproduce different times) Isolation Different courtship patterns, hibernation or estivation patterns, living habits, etc. May totally be different where two populations are no longer able to reproduce Wood frogs mate in late March, Leopard frogs mate in mid April

Since both are of the genus Rana, they can interbreed but do not Wood & Leopard Frogs 2. Geographic Isolation Physical barriers separated populations. Over time, they develop two totally different gene pools African Elephant is classified into 3 groups based on DNA West African elephants

Forests of C. Africa Savanna elephants of S & E. Africa 3. Reproductive isolation Results from Behavioral, Geographic and Temporal Isolation. Two populations can no longer interbreed to produce viable (sterile) offspring The story of the fruit flies

1. 2. 3. 4. A bunch of flies were minding their own business eating a banana A hurricane washed the banana & flies onto an island Since conditions & food are different on the island, the flies evolve separate from their mainland relatives When some of the flies mix with the mainland relatives, they can no longer produce viable offspring when they mate. New island

Speciation has occurred!! Mainland Mainland 99.9% of all species that ever inhabited this earth have gone extinct!! Mass extinctions Leave open habitats/niches to be filled by surviving populations. Leads to evolution of new species When dinosaurs went extinct, mammals were able to occupy open niches left by

the dinosaurs What if the land became dry due to global warming. Where would it be safe to inhabit? What modifications would be necessary to do so? Convergent Evolution Unrelated organisms that look alike but have evolved totally isolated from one another Analogous structures same function, different structure (sometimes) Fish, dolphins, tadpoles, penguins, seals Birds, bats, insects, flying squirrels

Worm and Snake Video Hummingbird Hummingbird moth Spurge Cactus These plants appear to be cactus plants, but the one to the far left is a spurge, not a true cactus. Both the cactus & spurge have reduced, spiny leaves to prevent water loss & a large succulent

stem for water storage. They are quite different plants though, Spurges have a milky latex-like fluid in the stem. This similar adaptation to their dry environment is an example of Convergent Evolution. Coevolution Two totally unrelated species evolve in response to changes in each other over time. Bees dont see red, but do see yellow, blue, and UV. Thus, bee-pollinated flowers are mostly yellow or blue with UV nectar guides (landing patterns) to guide the bee Birds, like hummingbirds have good eyes

which can see red Acacia tree and ants How quickly does evolution occur? Gradualism evolution is a constant process and occurs at a steady rate Punctuated equilibriumPeriods of equilibrium followed by rapid periods of change.

Change occurs w/ environmental pressures Species arise abruptly then have long periods of little change The Man and his theory You want proof?

We win!! Close but no cigar! Words, words, words Its all new Name of his famous book Organisms in rock

Individuals in nature differ from one another Hutton and Lyell felt this about the earth A change in a species over time Formation of a new species What he didn't

know was the source of variations What the video Children of Evolution demonstrated What happens when organisms produce more than can survive Proposed the theory that organisms change due to a need

to change Species branching off from a common ancestor What is necessary in order to be members of the same species Where he believed all those organisms came from

What the Amino Acid evidence sheet showed us Limited resources will be available so this will occur Main fault with the above theory Two species becoming more alike because of a common niche

Populations that can no longer reproduce with each other Where his voyage took him Differences in hemoglobin & cytochrome C between us & a chimp Natural variations

lead to advantages and disadvantages Economist who felt that populations if left unchecked, will suffer from disease famine & war "Ontogeny recapitulate Phylogeny" When two populations are

separated by a physical barrier like a mountain The organisms he used to formulate his theory Our forearm, the wings of a bird & the flipper of a whale with the same structure All organisms are united into a single

tree of life Concept that the environment selects which organisms are the best adapted Farmers selecting the most desirable traits for their livestock Two populations unable to interbreed because of different reproductive cycles

What he said caused the finches to differ from island to island Structures like our appendix that no longer serve a function Source of variations in a population

What happened to the nonbeneficial allele in our Natural Selection lab The wings of a bat and the wings of a fly An orchid and its pollinating insect evolving together % of all species that are now extinct

Why the dark peppered moth's frequency increased after the English Industrial Revolution What introduced species did to the Galapagos native species Occuring in small populations, a certain trait might get passed

on more than another Concept that evolution occurs in spurts due to sudden environmental pressures Name his famous ship and the years of his voyage The Man and his theory You want

proof? We win!! Close but no cigar! Words, words, words Its all new Natural variations The earth was very

old and that the forces that changed it are still happening today Evolution Speciation Divergent evolution Must be able to breed and produce a reproductive offspring

On the Origin of Species Fossils Genetics and the source of variations Comparative Embryology Overpopulation

Lamarck's theory of inheritance of acquired traits A common ancestor Comparative Biochemistry. Similar proteins would be coded for by similar DNA Leads to competition for

limited resources Acquired characteristics or traits can not be passed to offspring Convergent evolution Separate species Around the Southern Hemisphere and

the Galapagos Islands No difference. Nearest living relative Survival of the fittest Thomas Malthus Our development repeats the evolution of our species

Geographic isolation Marine iquana, Galapagos tortoise and finches Homologous structures indicating divergent evolution Share a common ancestor Natural Selection

Selective breeding Behavioral or Temporal isolation Vestigial structures Mutations, genetic recombination & sexual reproduction Nonbeneficial allele frequencies will decrease

Analogous structures Coevolution 99.90% Darker moths blended in with the darkened trees. Harder for the birds to see them to eat them Destroy or disrupt native species

(extinction of iguanas on the islands) Genetic Drift Punctuated Equilibrium Adaptive radiation (started as one species and filled open niches based on variations) HMS Beagle from 1831 - 1835

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