Lecture 16: Evolution After Darwin - Mendel and Genetics PDF

Lecture 16: Evolution after Darwin: Mendel and the beginnings of genetics ● Why did Darwin give up Christianity? ● He thinks there is not enough evidence for it. ● Was he an atheist or agnostic? He called himself agnostic. But knowing what he thought, we should call him a deist rather than agnostic....

Lecture 16: Evolution after Darwin: Mendel and the beginnings of genetics ● Why did Darwin give up Christianity? ● He thinks there is not enough evidence for it. ● Was he an atheist or agnostic? He called himself agnostic. But knowing what he thought, we should call him a deist rather than agnostic. ● Darwin was not an atheist, but a deist; that is, he believed that some creating intelligence had designed the universe and set up natural laws according to which all of nature was unwaveringly governed. ● Dr. John emphasises the compatibility with Darwin and religion etc... To make up for the many garbage on the net and popular media. ● Nevertheless, according to some interpretations, Darwin’s theories are contradictory with some religious beliefs. ● Things that look like contradictory in the past have always been reconciled somehow. ● What flowers did Darwin work on to show the same results as Mendel? SNAPDRAGON Darwin in 1881 ● Darwin first noticed the action of worms in 1830s when he visit his uncle at his estate 🡪 his uncle pointed that the patch of ground where someone had sprinkled some material on many years before and this material is now completely gone ▪ Uncle suggest that it is worms. So Darwin was curious why material don’t just stay there, it sinks ● This started his interest in earth worms. Darwin’s last book: The formation of vegetable mould, through the action of worms, with observations on their habits (1881) ● His last book. Published 6 months before he died. ▪ Instant bestseller due to interesting findings ▪ Of course there were critics in comics also ● Vegetable Mould – just means soil. ● How is soil formed by worms? ▪ He studied soils and worms ● Why is it that archaeological things always underground? Why is it not in the surface? ▪ The most common reason: Things have been buried by earthworm. As Darwin has showed in his book. ▪ The humble little worm has a huge impact on the environment and is more productive than any animal we are aware of ▪ Prevents leaves from piling up, air the soil and pull rotting vegetation down inside and change the dirt to fertile soil Worm castings ● These are the regurgitated dirt that worms have cough out from its mouth after it has digested the digestible stuff from it. ● What Darwin noticed; the tiny bit of sand goes up the earth. It has been pushed up, just a tiny bit of sand has gone up. ▪ This is how object sink 🡪 Using Darwinian observation, the power of cumulative occurrence. Any object that is bigger than the worm’s mouth will not be touched and thus sink. E.g. the roman tile floor from an ancient roman villa. They did not build it underground. It is through the power of reiteration, the worm ingests soil and other material, expel those that they cannot expel. The earthworm put soil above present surface of land. The dirt is meaningless but repeated over many times, it become significant. Darwin wanted to understand how worm works ● Once again, some unusual, but very original, experiments… ● Can worms hear? Sense vibrations? ● Are they intelligent? ● Hear 🡪 Darwin concluded worms cannot hear. (had his wife play the piano beside them, son play the basqic, shine the light of different colour on them at night) Worms react to vibrations. They fill their stomach with dried leaves. ● Intelligence 🡪 Constructed fake leaves using pieces of paper in different shapes, like triangle. Darwin found 80% of the case, the worms pull the leaves by the tip of the triangle, he concludes that though they do not have eyes or brain, they can distinguish the shape. They have basic forms of intelligence. The simplest creature still has some sort of intelligence. ▪ Tip of the triangle was the easiest to pull down into the burrows of their hole ● Major point of the book: show that these little ignored animals utterly transformed the world. We cannot survive without them. Cumulative effect of their action completely change the surface of the earth. ▪ Soil is made by worms. They help to fertilise the soils. ▪ They also round of landscape. ▪ Helps plants grow (produce soil) ● Soils are made by worms, they simply do not exist. Soils are not dirt or sand, they have biological matter in them. Soils are biological products. Worms aerate soil by their burrows, turnover soils and round around (smooth and soften) the landscape. Very fitting book to be his last book. All essential ingredients. Numerous little changes caused a huge change over a period of long time and no one has seen it before. The worm stone ● Two metal bars driven into the bedrock ● A stone donut placed on surface of the lawn. ● Use this to measure how quickly or slowly the stone sank because of the worms ● Found out that worms are only active to a certain level of depth Reactions to Darwin’s death (in 1882) ● 6 months later, Darwin died of heart trouble. ● Surprisingly, the reactions to Darwin’s death are extraordinary, even before biographies of Darwin was written. ▪ Newspapers even report his death ▪ Alfred Russel Wallace 1883 🡪 Darwin was the “Philosopher who has wrought a greater revolution in human thought within a quarter of a century than any man of our time – or conceptions of the world of life, and a theory which is itself a powerful instrument of research; has shown us how to combine into one consistent whole the facts accumulated by all the separate classes of workers, and has thereby revolutionised the whole study of nature ● These reactions are based on their own reading of Darwin. ● More statues in China than compared to anywhere else in the world. ● 1885 unveiling of the statue of Darwin, at the Natural History Museum, London. ▪ Richard Owen is director, rival 🡪 statue was replaced ▪ Till 2009, they returned the statue of Darwin back to this place instead of owen CHALLENGES OF DARWIN THEORY OF NATURAL SELECTION (SLOW AND GRADUAL PROCESS) Francis Galton (1822-1911) ● Darwin’s cousin. ● He wanted to test Darwin’s provision hypothesis, pangenesis (development theory of heredity: All cells in an organism are capable of shedding minute particles called gemmules which can circulate throughout the body and finally congregate in the gonads.) ● Who did tests on bunnies and found out that nothing is passed on ▪ Statistical methods to study heredity ● Darwin rejected his claim as primitive animal do not have blood and plants do not have blood. ● First person to introduce rigorous statistical methods to study heredity. / pioneer ▪ Took the brown rabbits and added their blood into white rabbits but they did not produce brown rabbits ▪ Published findings in paper ▪ Darwin responded by saying I never said heredity was in the blood ● Darwin was not mathematically inclined August Weissman (1834-1914) ● German, one of Darwin’s contemporaries. Introduced a radical change for the first time. ● All the way back to Lamarck and before him, naturalist believed that acquired characteristics can be inherited. ● Weissman said it cannot. ● Germ plasm theory (1896-1910) ● ● ● ● ● ▪ Germ cells (germinate) 🡪 starting cells (not germs) inheritance (in a multicellular organism) only goes through germ cells: egg cells and sperm cells (sex cells), not body cells. ▪ That’s why you can modify an animal and it will not be passed on ▪ Properties of body cells does not go to the offspring. But it is all passed by the germ cells ▪ The recipe is in the germ cell. What is given to the offspring is in the reproductive cells. Like when you cut the tails of a mouse, the offspring still have tails and, Jews have to circumcised. ▪ Changes cannot be passed on. (modification of the adult body, cannot be passed on) Wallace was one of the early people to agree with this. Which means no inheritance of acquired characteristics (what your textbooks incorrectly call ‘Lamarckism’) ▪ Vague ideas of these has been held for centuries by naturalists and Darwin himself had such ideas too Gregor Mendel (1822-1884) ● German speaker ● Botanist and priest and naturalist (nothing unusual) ● He is NOT the founder of genetics ● Studied some science but very mathematically inclined. ● Whose work did Mendel work on and try to prove? Linnaeus ● Made very famous experiments on pea plants ● 1843 begin training as a priest, 1843 Augustinian Abbey of St Thomas in Brno, 1851-1853 University of Vienna, 1856-1863 pea plants, 1867 became Abbot - Eventually became a monk ● He got promoted to administration. Became Abbot and no longer did any science. Gregor Mendel Experiments on hybridity and inheritance in pea plants Published 1865 – 1866 ● He had a garden and experimented with different peas (crossing cross fertilise types of peas) ▪ To find the offsprings ▪ Plump vs wrinkled pod ▪ Tall plant vs short plant ▪ Round vs wrinkled pea ▪ Green vs yellow pod ▪ White vs purple flower ● There are some characteristics that these plants have this or that and not in between. ● He wanted to study how these properties of these organism was passed on. ● Through thousands of crossings. He discovered ratio 3:1. Mendel’s discovery of 3:1 ratio ● What he is famous now for. ▪ His paper was previously ignored ● Dominant and recessive genes (refer to picture) ▪ Mixed white and red ▪ Second generation all red ▪ Third generation, 3 red and one white 🡪 show that inside them, there were characteristics of the white feature in the 2nd generation ▪ This means the characteristics of white invisibly passed through the red ones invisibly. At the third generation. ● Other naturalists have also showed the offspring heredity theory (breeding experiments), including Darwin ▪ But Darwin did not have a mathematical mind, which Mendel did (crucial for future) ● Mendel thought that by experimenting with hybrid, he is challenging Darwin. (coming up with a better theory of evolution) ▪ Though he was called the founder of modern genetics 🡪 he didn’t have this objective. ▪ New things occur by mixing genetics ● What he showed: The way characteristics are inherited is not the way Darwin and earlier people had thought. They thought they just simply mix or blend, get a ‘halfway’ characteristics. ▪ Heredity was particulate (not just mixed/blending) and inheritance patterns of many traits can be explained through simple rules and ratios ● He found that, when you cross two different types (make them have sex), what you get is loads of red. (blending argument - Fleeming, who assume inheritance is mix in stuff. What Mendel found, subsequent generation will have 3 red and 1 white. The whiteness was inside the previous gen. They carried the heredity particle inside them. In this case red is dominant. It shows that heredity is not like mixing pots of paint. Heredity is in discrete particles or chunks. The inheritance follows simple mathematical law ● Opened the way to the study of genetics. Mendel’s two laws ● Usually textbook description, but is not true 🡪 retrospective descriptions of what Mendel was doing ● Law of segregation ▪ Individual possesses a pair of ‘alleles’ (alternative versions of a gene) for a trait. ▪ Sex cells get only one of the pair ▪ Offspring thus gets its own pair ▪ Whichever is dominant will be expressed… but the recessive one is still inside. ● Law of Independent Assortment ▪ different traits are inherited independently of each other (not mixed in blended) ▪ Colours of flowers do not affect the shape of the seeds – example of independent assortment. Did Darwin know of Mendel’s work? ● Mendel’s work was ignored or unappreciated during his lifetime (Publish in obscure German work) ● Widespread legend: Darwin had a copy of Mendel’s work on his desk unopened. If only Darwin had read Mendel, science would have revolutionised again. ● This is not true. Darwin DID NOT have Mendel’s work. ● Darwin probably would not appreciate it just like any other. People just did not get it. It did not take off. In fact, Mendel was forgotten for a long time. Hugo de Vries ● A Dutchman. ● 1889: de Vries postulated that “inheritance of specific traits in organisms comes in particles” which he called “pangenes” ● Pangenes – named after Darwin’s theory, pangenesis ▪ Later shorterned to genes ● He thought there were these little particles, prepared him to appreciate Mendel’s work. ● 3 people rediscovered Mendel on the same year ● Came up with the theory of mutation 1900 Mendel is rediscovered ● Hugo de Vries, Carl Correns and Erich von Tschermak ● These 3 realised Mendel made a great discovery. ● Probably, there are scientific naughtiness. But these 3 people realised Mendel found a great discovery. ▪ They were inspired by Mendel to understand modern genetics 🡪 this is different from Mendel inventing modern genetics ▪ Mendel DID NOT invent modern genetics Mutation theory ● De Vries🡪 new forms of primroses appearing– called these mutations ▪ Similar to what Wallace was talking about, parents born of the normal type but the offspring is quite different 🡪 mutant ● Combined with Galton’s statistics he created a new theory for the origin of species: mutation theory ● Was mutationism an alternative to Darwinism? Originally thought they were different. ▪ De Vries thought that this was how new forms came about, rather than Darwin’s theory of slow system of natural selection ▪ NOTE: *Everyone accepted theory of evolution, but did not accept how did evolution work ● De vries made interesting discovery. Found primroses growing itself in the field unattended. Grew by itself to new colours and varieties. Look different from normal look. ● Here is a mechanism where they can become different without natural selection. ● Mutation theory, thought as a rival to Darwin’s theory. ● It was thought to be a death knell to Darwin’s theory. ● Field naturalists – 100% Darwinian. Look old fashioned ● Laboratory naturalists – with white coats and microscopes, think more superior 1903 Walter Sutton and Theodor Boveri ● suggested that chromosomes, which segregate or split in a Mendelian way (during cell division, are hereditary units… ● This was done with a microscope of the period. They could not see it; they have to stain the cells with colour which kill them. What they saw was loads and loads of individual cells in different stages. ● These chromosomes separate off to 2 pieces, fit into Mendelian way of prediction. ▪ Genes are in the chromosomes Thomas Hunt Morgan ● American ● Morgan sought to prove Mutation Theory with his experiments breeding fruit flies ● 1910 Morgan showed that genes are on chromosomes ● 1915 Morgan combined Mendel's theories with Chromosome Theory of Inheritance. ▪ He thought that his theory was challenge Darwinism ▪ He incorrectly believed natural selection could only eliminate the unfit… Darwin says natural selection creates novelty. ▪ The source of newness, could only be mutation ▪ They thought they were against Darwin (old fashion biology) ● He did not believe natural selection can bring about any novelty (only mutation can be the source of new features) 🡪 dogma for the time which is a myth ● Greatest source of novelty: sexual reproduction. The offspring is completely a unique creature. Mutation is what we hear about. The modern synthesis c. 1936-1947 ● Mendelian genetics (Mendel) and Darwinian natural selection are found to be compatible – and indeed genetics becomes one of the most powerful confirmations of evolution by natural selection ● Mutation was a major source which natural selection picks to adapt things Watson and crick discover the structure of DNA, 1953 ● Their discovery contributed to the advent of modern molecular genetics ● Actual structure of DNA, actual molecule in cell AGE OF THE EARTH The age of the earth (yet again) ● Biggest contest of the age of the earth after origin of species ● Ernest Rutherford and radiometric dating. A physicist. ▪ Use new discovery called radioactivity to apply to dating rocks. ▪ Most rocks give off various particles as they decay at a rate that is constant. ▪ From the time the rock is formed it gives out particles. You can measure how much percentage is left. ▪ With the discovery of radioactivity, scientist can quickly estimate the age of the earth ● The meteorite are remnants of the material floating around the space before our solar system is created. ● Led to the discovery that the earth is about 4.5 billion years old The mystery of the Wallace line ● Surface of the earth is made out of plates (liquid rocks, magna) ▪ Churning the fire interior of the earth (then when earth plates are stuck, will have earthquakes etc) ▪ So we if reconstructed the movement of plates, will understand why Victorian times discovery didn’t make sense (including Wallace line) ● Wallace line. 1863 (Asian vs Australian species on the other side of the line) ▪ South America (Australian line started on the other side of the world), then they moved without mixing, slowly coming into contact with Asian plate ● Australian plate is moving like a bulldozer, so some materials between the Asian and Australian plate are actually pushed up from within the earth by the Australian plate (like East Timor) ▪ The reason this is unique. Usually there is continents or ocean in between when there are unrelated families. ● But this is right next to each other. Wallace and his contemporaries cannot explain. ● Shows where marsupials live today – Australia ● Complete opposite ends of the world. ● Should have intermediate families in between. The theory of continental drift ● First proposed by German meteorologist. Alfred Wegener (1880-1930) ▪ Was considered a laughing stock ▪ Textbooks always say Wegener was laughed at or ignored because he does not have a mechanism. ● He is not the first to think that continents look like a jigsaw puzzle. ▪ Africa and south America look like they fit together ▪ Continental shapes ● He had evidence, the rocks of either side of the ocean were identical rocks. They contained exact fossil types. (rock types and fossil matches) ▪ Rocks in Africa was found to match rocks in south America 🡪 showing drift ● People found tropical species in Europe. He explained due to the earth’s movement. (Continental drift but nowadays we said plate tectonics instead) ● His evidence is good and compelling. The lands must have moved. ● He died in Greenland on an expedition (glazier). He was buried there in the ice. Which means Wegener body have been drifting in ice for about an inch a year. Plate tectonics 1950-1960s ● A lot of new things were put to together to accept, plate tectonics during this period. ● Palaeomagnetism – earth magnetic field has reversed many times in many million years in the course of history. We do not know why. It just switches. (North and south pole) ▪ When rocks are molten like lava, the little particples in them are magnetic ▪ Liquid state, particles can move ▪ Magnetic ion particles in rock are aligned according to where the magnetic north pole is. ● If you investigate different rocks of different ages (Frozen), they all point differently. Some point north, some point south. Pointing all over the place because the land moved. 🡪 can know which direction the rock is facing when it surfaced ● They drag this magnetic detector over the earth and see the magnetic force. They found that down the centre of Atlantic Ocean, there is a crack (mid Atlantic ridge), the magnetic pole mirror in the crack, the surface of the earth come out from the crack. (new rock is being formed and flows up, as surface of earth crust is moving, new rocks will be spreading away) ● Magnetic pole of the earth occasionally flip. When the new rock is liquid, the magnetic particles will point north, when cooled will be stuck in that direction. Saw that the series of flip on either side of the mid Atlantic ridge and they are symmetrical. ● Sea floor spreading – discovered after 2nd world war when cold war kicked off. Necessary to map the undersea using magnetic stripping. Discovered that there was a gigantic mountain ridge all the way running down the planet, like a mirror image. How are old rocks at the bottom of the earth? The rocks on the sea floor were very young. ▪ The closer you are to the ridge the younger the rocks are. That is why the sea floor rocks are younger because they are still being made. ● Some of the problems Darwin and his contemporaries cannot solve is because they are unaware of this theory. ● The solution to mystery of Wallace line, is this. Australia and Antarctica were once connected with south America, where marsupials evolved.