Unit5 biological evolution


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Unit5 biological evolution

  4. 4. RELIGIOUS/MYTHICAL EXPLANATIONS: Based on Faith A supernatural being created the world the way we see it. PHILOSOPHICAL EXPLANATIONS: Based on Reason Anaximander of Miletus: (610-546 B.C.) Aristotle: (384-332 B.C.) SCIENTIFIC EXPLANATIONS: Based on the Scientific Method Question/problem etc. ✔ Observation of facts (reality) ✔ Proposing THEORIES that explain those facts, through the use of REASON. ✔ Constant testing of these theories with new observations: REVISION and IMPROVEMENT of the theories. ✔
  5. 5. SPONTANEOUS GENERATION - For a long time people believed that living beings -at least the simplest forms of lifewere originated from non-living matter, normally decaying matter. This is called SPONTANEOUS GENERATION. - Although wrong, this theory was supported by many everyday observations: small insects seemed to emerge from rotten meat, rats from dumps, worms from mud... Jan Baptist van Helmont (1579-1644): He experimented with plants, growing them and comparing their increase in size with the insignificant loss in the soil: he deduced it was the water that formed the new living mass (photosynthesis had not been discovered). He also had a peculiar recipe for mice (“place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear”) and scorpions ( “basil, placed between two bricks and left in sunlight”) +
  6. 6. Francesco Redi (1626-1697): - First to try to falsify Spontaneous Generation. - He designed an experiment to prove that flies don't arise from rotten meat by spontaneous generation, but from maggots: he placed pieces of meat in open and closed jars (some sealed, some covered with a cloth to allow air into them), and observed that flies only appeared in the open ones. In spite of Redi's results, the discovery of microorganisms gave fresh air to Spontaneous Generation
  7. 7. Lazaro Spallanzani (1729-1799): He boiled broth in an open flask and observed that microorganisms appeared, while if the boiled broth was kept in closed flasks this didn't happen. He was criticised by saying that he had only proved that life could not survive without air.
  8. 8. The End of Spontaneous Generation: Louis Pasteur (1822-1895) - French chemist and one of the first microbiologists. - He supported the Germ Theory of Disease. Pasteur was a great scientist and among his contributions to science are: - The first VACCINES (anthrax, rabies): one of the founders of Immunology. - The invention of a method to prevent milk and wine from causing sickness: PASTEURIZATION - The experiment that put a definitive end to the theory of spontaneous generation:
  9. 9. In 1859 Pasteur boiled a meat broth in a flask that had a long neck which curved downward, like a goose (“col de cygne” = swan neck). The bend in the neck prevented any particles from reaching the broth, while still allowing the free flow of air. Nothing grew inside the flask unless when it was broken. This experiment put a definitive end to the theory of spontaneous generation, and also supported the Germ Theory.
  10. 10. "Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment" said Pasteur in his triumphant lecture at the Sorbonne in 1864. Pasteur proved that all living beings, no matter their size, came from other living beings. But... How did life start in the first place?
  11. 11. Extraterrestrial origins: PANSPERMIA In the 19th and 20th centuries some scientists supported the theory that life might have arrived to the Earth in the form of bacteria carried by meteorites, or even sown by other intelligent extraterrestrial beings. Cons: the conditions these bacteria must have endured in their journey through space are really extreme (ultraviolet radiation, extremely cold temperatures, etc) Among the supporters of this theory were: Chemist Svante Arrhenius (1859-1927) Astronomer Fred Hoyle (1915-2001) But does Panspermia really answer the question of the Origins of Life? NO! IT ONLY DIVERTS IT TO OTHER PLACES IN THE UNIVERSE
  12. 12. Biochemical explanations: Oparin's Hypothesis Alexander Oparin (1894-1980): 1º) The first organic molecules originated through the reactions of the gases of the primitive atmosphere, using the energy of the electrical storms (lightning) and ultraviolet radiation from the sun. 2º) These organic molecules would gather in the ocean for millions of years, becoming a primordial soup in which molecules reacted and - At some moment, some became more and more complex. of these molecules would be able to auto-replicate. - Some of these autoreplicating molecules would be isolated in tiny structures: coacervates - These coacervates would later originate the first cells
  14. 14. The Miller Experiment (1953) Stanley Lloyd Miller (1930-2007:) - He designed an experiment to test the first steps of Oparin's Hypothesis. - He reproduced the conditions of the primitive atmosphere in his lab, and found that after some time small organic molecules such as amino acids were formed. Miller DID NOT create life in his lab, but he proved that life may have begun from a chemical evolution.
  15. 15. What is Biological Evolution? - Evolution is the change in the inherited traits in one population over time. This change produces a gradual transformation of simple living things into more complex species across the generations.
  16. 16. FIXIST THEORIES: - For a long time, until the 19th century, most people believed that all the species on Earth were invariable and stable, and had been created the way we see them today. - This was supported by the literal interpretation of the Bible, which many people, scientists included, took for a scientific book. Aristotle's Great Chain of Being Carl von Linnaeus (1707-1778) Father of Taxonomy
  17. 17. As time went by, evidences in favour of Evolution piled up: - fossils - proves of an older Earth than the one described in the Bible Plesyosaurus But fossils were Ichtyosaurus still explained by many as nature's whims, God's Mary Anning (1799-1847) a famous British fossil collector who made many great discoveries of fossils in the cliffs of Lyme, such as the first specimen of Ichtyosaurus and the first Plesyosaurus. Her findings helped to scientifically prove EXTINCTION. jokes, or the remains of animals that hadn't survived the Flood.
  18. 18. Georges Cuvier (1769-1832): - French naturalist who established EXTINCTION as a fact. - He explained the existence of fossils with his theory of CATASTROPHISM: the fossils were the remains of animals that had died during past geological catastrophes. - Still, Cuvier was a fixist: according to him fossils were the result of “successive creations” to replace the extinct species after each catastrophe. He counted up to 27 different creations. - Presumably, the last catastrophe had been the Universal Flood.
  19. 19. The Fossil Record
  20. 20. FIRST EVOLUTIONARY THEORIES: Erasmus Darwin: (1731 – 1802): - He belonged to the British Enlightment movement: he was a natural philosopher, doctor (he refused to be king's George III's personal physician), abolitionist and poet. - In his work Zoönomia he expressed some views that foreshadowed a theory of evolution, which were read and commented on by his grandson Charles Darwin. - In addition to being an abolitionist, Erasmus Darwin advocated a proper education for girls: they should be educated in schools and learn proper subjects like physical exercise, botany, chemistry, mineralogy, etc. - Although Erasmus's evolutionary ideas were primitive and more poetical than scientifically grounded (his poem The Botanic Garden offered a glimpse of evolution), his free-thinking had undoubtedley an important influence on his grandson Charles.
  21. 21. Jean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck, known as Lamarck: (1744-1829) - French soldier and naturalist, first to formulate a theory of evolution, that included a mechanism, however wrong, for it. He was also one of the first in using the term “Biology” in its modern sense. Lamarck's theory was based in the following principles: - The ENVIRONMENT is able to induce changes in animals. - In all the organisms there is a drive to PERFECTION, a force that makes them change from more simple to more complex and to be better adapted to their environment. - If an organism needs a new organ for a new function, it will develop it: the FUNCTION creates the ORGAN. - ADAPTATION: when there is a change in the environment, the organisms also change to be better adapted to it. These changes are always beneficial, never damaging. - USE AND DISUSE: the more an animal uses an organ, the more developed it becomes. Organs that are seldom used weaken and finally disappear. - INHERITANCE OF ACQUIRED CHARACTERISTICS: once an individual has developed a feature, this is transmitted to the offspring. Although wrong, this was shared by many scientists, Darwin included, as they didn't know how characters are transmitted from parents to offspring (GENETICS).
  22. 22. BUT inherited traits acquired during lifetime are not transmitted to the offspring, as German biologist August Weismann proved: Weismann cut the tails off mice, then crossed them, and checked the offspring. If a mouse without a tail produced offspring without tails it would be the ultimate example of Lamarck's definition of disuse. If Lamarck was correct, the disuse of a tail due to removal would be passed on to successive generations. Weismann cut the tails off 901 mice over 5 generations. His results? Every mouse, in every generation, was born with a normal tail.
  23. 23. Charles Robert Darwin (Shrewsbury, 12th February, 1809 -Downe, 19th April, 1882): Evolution by NATURAL SELECTION: - Living beings produce larger offsprings that can survive with the limited resources of the environment: - Individuals in the populations are not identical: there are small inheritable differences among them. - Struggle to survive: Only the fittest, most adapted to the environment, survive. - The individuals that survive transmit their inheritable traits to their offspring. - The accumulation of small variations through many generations produce the new adaptations to the environment.
  24. 24. Charles Darwin: Evolution through Natural Selection - there is a natural variability of inheritable traits in a population. - some of these traits give an advantage to the individuals to survive and leave more offspring in a certain environment, so they are transmitted to the next generation in a higher frequency: they are favoured by Natural Selection. - changes add over time through the generations and produce the adaptations
  25. 25. Not all offspring survive to become adults. Those with favourable variations, such as long, thick fur in a cold environment, are more likely to survive and leave offspring than those without. This effect of different characteristics on survival is what Charles Darwin called NATURAL SELECTION.
  26. 26. BUT: What would happen if the beetles lived on the grass or on the leaves of the trees instead of on the bark? THERE ARE NOT “GOOD” OR “BAD” TRAITS: NATURAL SELECTION DEPENDS ON THE ENVIRONMENT
  27. 27. - The environment induces the organisms to change. - These changes are always positive (perfection drive) - Use and disuse. ✗ - Inheritance of acquired characters (ALSO SHARED BY DARWIN!!!) Lamarck's theory Darwin's theory - Pre-existing variation - Not all the variations are equally adaptative in a given environment. -S truggle to survive: The best adapted survive and leave more offspring: the next generation will be better adapted (survival of the fittest)
  28. 28. Let's learn a bit more about who Charles Darwin was and how he got to develop his theory: - Son of a doctor, Robert Darwin (very strict with his children), and grandson of the proto-evolutionist Erasmus; his mother died when he was a child. He showed a deep interest in nature since his childhood. Darwin's birthplace The 7- year- old Darwin
  29. 29. The young Darwin was not a good student, and after attending the Shrewsbury school he moved at the age of 16 to study in the University of Edinburgh Medical School to become a doctor, like his father. After witnessing the bloody surgeries that were performed in the operating theatres of the time (no anaesthesia!) he convinced himself that he could never be a doctor, and left Edinburgh in only two years. However, it was there that he heard for the first time about Lamarck's evolutionary ideas, which made no impression on him, as his own grandfather's hadn't either. After leaving Edinburgh, Darwin went to Cambridge's Christ College, where he was to study Theology to become an Anglican parson. There he met the botany professor John Stevens Henslow. He was the one who proposed the young Darwin (only 21!) for the position of companion -rather than naturalist- to captain Robert Fitzroy, who was to start an almost 5-years voyage around the world in the H.M.S. Beagle. University of Edinburgh Christ College, Cambridge
  30. 30. John Stevens Henslow, professor of Botanics at Cambridge, RECOMENDED.... the young Darwin (21) to Captain Robert Fitzroy (26) (who accepted him in spite of his nose!) for one of the most exciting voyages, that was about to change the history of Science
  31. 31. The HMS Beagle, in her second voyage left Plymouth on 27th December, 1831 and returned to Falmouth, Cornwall, on 2nd October, 1836 27,5 m long, 7,46 width... and 75 people to live in it!!! and Darwin, who shared Fitzroy's cabin, was sea-sicked most of the time...!
  32. 32. But the Darwin that had left England in the Beagle was an unknown young naturalist that shared the fixist views of his times... and the one that returned almost 5 years later was a famous scientist because of the amazing discoveries of new species that he had made, and, most important: HE HAD A SECRET, a revolutionary theory that he still did not dare to share with his fellow scientists... a theory of EVOLUTION, with the right mechanism: NATURAL SELECTION
  33. 33. What had happened in this voyage...? - During the voyage on the Beagle, Darwin collected and discovered plentiful of new species that he sent to England in every stop of the ship, and studied the geology of the South American lands. His observations were influenced by his previous knowledge and his new readings: Charles Lyell, geologist, and his Principles of Geology, in which he pointed out that the earth was shaped by slow-moving forces still operating today (UNIFORMITANIARISM): slow forces could make big changes if given the time. Captain Fitzroy had given the book to Darwin as a gift when they started their voyage.. Thomas Malthus, demographer and economist, who in his An Essay on the Principle of Population (published 1798) stated that “the population grows faster than the resources” Darwin read Malthus work soon after he returned to England.
  34. 34. And then, he arrived to the Galapago Islands...
  35. 35. Each island had a slightly different finch species, each perfectly adapted to its diet. Why had God bothered to create a slightly different species for each island?
  36. 36. Darwin had the genius to see the importance of what all the other scientists of his time had dismissed as unimportant: VARIATION among the individuals: If in one island the main nourishment was seeds then the finches with a hard peak, able to open them would have an advantage from the others, and would leave more offspring with the same features ✔ If in other island they need to peck on wood, or suck nectar from the flowers, other shapes of peaks were favoured, . ✔ So after many generations (TIME) the population of each island had different peaks. ✔ Darwin called NATURAL SELECTION this mechanism that chooses (selects) from the different VARIETIES present in a population the best adapted for a certain environment. As these leave more offspring than the others, after enough TIME had passed, the characteristics of the population are changed. If many changes accumulate over time, a new species would be originated. ✔
  37. 37. DIFFERENT SPECIES, ADAPTED TO DIFFERENT ENVIRONMENTS One population of slightly different finches: VARIATION in the population + Different environments ( NATURAL SELECTION) + TIME
  38. 38. Back in England, Darwin was famous and introduced to the most important scientists of the time. Although he had already shaped his theory of Evolution through Natural Selection in his mind, instead of staying in London, he decided to marry his cousin Emma and retire to Downe House, in Down (Kent), from where he kept in touch with the scientific world through the post mail. Emma Darwin was very religious and liked to play the piano (she had studied with Chopin).
  39. 39. Downe House In his greenhouse Darwin experimented with different plants (carnivorous plants, orchids...) and published books on his findings. He was also a world expert on barnacles!
  40. 40. Darwin was a loving father, not at all strict, and loved to play with his children George Darwin, mathematician Charles with his son William Annie. Her death at the age of 10 deeply affected Darwin. Emma Darwin Francis Darwin, scientist
  41. 41. Although Darwin continued studying different fields of science, and corresponding with hundreds of scientists all around the world on different matters, he seemed in no hurry to publish the theory which he knew, would make him pass into history... WHY...??? Darwin used to walk along his sandwalk in Downe House, thinking about his scientific theories.
  42. 42. - He knew his Theory of Evolution would bring him problems with the Church, and maybe he didn't want to hurt his wife, Emma. - He knew his theory might also be polemical among the scientists, and wanted to have it well grounded with enough proves and examples. - He knew the WEAK POINTS of his theory: he didn't know HOW VARIATION WAS ORIGINATED, and HOW FEATURES WERE TRANSMITTED TO THE OFFSPRING (in fact, he believed in the inheritance of acquired features, like Lamarck). HE HAD NO CHOICE: GENETICS WAS BEING DISCOVERED AT THAT TIME by an obscure Czech monk, GREGOR MENDEL.
  43. 43. So, only after receiving a letter from another naturalist, ALFRED RUSSELL WALLACE, who had reached very similar conclusions as his, did he decide to publish his book, On the Origins of Species by Means of Natural Selection, on 22nd November, 1859, more than 20 years after the end of his voyage in the Beagle! The book was an immediate success in sales, and a controversy began among the population (actually, the scientific communitiy accepted it quite quickly)... Old Wallace Alfred Russell Wallace (1823-1913). He independently reached a theory of evolution due to natural selection that prompted Charles Darwin to publish his own theory. Unlike Darwin, the financial problems were a constant concern during his life, and Darwin was very aware of Wallace's financial problems and lobbied long and hard to get him a government pension for his lifetime contributions to science. A £200 annual pension was awarded in 1881 which helped to stabilise Wallace's financial position, in addition to the income from his writings. Darwin and him presented their theory together to the Linnean Society in London, on the 1st July, 1858 Young Wallace in Singapore.
  44. 44. First evolutionary tree Darwin avoided in this book the controversial term “evolution”, but he did insist on the common ancestor that all living beings shared. About the origins of life, the only alusion he made was “light will be thrown on the origin of man and his history". Only in a later book would he adress the origins of man: Descent of Man, 1871. The Origins of Species's final paragraph: “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved”
  46. 46. NEODARWINISM or SYNTHETIC THEORY: It fuses the theory of Natural Selection with the knowledge in Genetics that we have acquired all through the 20th and 21st centuries: - We now know that the inherited traits are in the GENES, made of DNA. - Any mistake in the copying of DNA (MUTATION) results in a different protein===> different trait: Now we have the source of VARIABILITY among the population: MUTATION - Evolution occurs GRADUALLY: small changes that accumulate over time
  47. 47. The NEO-DARWINISM or MODERN EVOLUTIONARY SYNTHESIS is the modern version of Evolution: ➔ Mechanism: NATURAL SELECTION ➔ Source of Variation: MUTATION, RECOMBINATION, GENETIC DRIFT ➔ Transmission of features: DNA (Genes) Theodosius Dobzhansky (1900-1975) “Nothing in Biology Makes Sense Unless in the Light of Evolution” Prominent geneticist and evolutionary biologist, and a central figure in the field of evolutionary biology for his work in shaping the unifying modern evolutionary synthesis. One of his most famous essays has as a title: His Spanish student Francisco José Ayala (1934- ) continued his work.
  48. 48. Richard Dawkins (1941- ), one of the most popular neo-darwinians due to his many books popularising science, such as The Selfish Gene, and his bold defence of science and reason against pseudosciences. “Living beings have been on Earth for more than 3000 million years without knowing why before the truth was at last known by one of them: By a man named Charles Darwin” "We are survival machines - robot vehicles blindly programmed to preserve the selfish molecules known as genes”
  49. 49. PUNCTUATED EQUILIBRIUM or SALTATIONISM: - it opposes gradualism: species go through long periods of stability followed by abrupt short periods of change: evolutionary change occurs relatively quickly, while most of the time species are stable. - this is consistent with the discontinuities that the fossil record shows (Neodarwinians explain these discontinuities by claiming the fossil record is incomplete) - CATASTROPHES - MACROMUTATIONS
  50. 50. Stephen Jay Gould (1941-2002) The deep impression that the huge T.rex in the hall of the American Museum of Natural History in New York were his father took him when he was only 5 decided him to become a paleontologist. Niles Eldredge (1943-) ✔ He started studying Latin at Columbia University, but soon switched to Anthropology, in which he graduated and completed his PhD. ✔ Very popular paleontologist and evolutionary biologist, most of all because of his many books popularizing Evolution. He worked in different universities and in ✔ He has been working in the American Museum of Natural History the American Museum of Natural History in New York since 1969. ✔ He was also active in the defense of the civil rights, fighting against racism, sexism, cultural oppression and pseudosciences, especially creationism and others used in the service of racism and sexism. ✔ American Museum of Natural History, New York
  51. 51. Both Gradualism and Punctuated Equilibrium accept Natural Selection as the mechanism for evolution. They disagree in the rythm of evolutionary change. ✔ GRADUALISM PUNCTUATED EQUILIBRIUM
  52. 52. How would Lamarck explain the following examples of evolution? And fixists? And Darwin? And Neodarwinians? Manchester's peppered moths (Biston betularia) Bacteria's resistance to antibiotics
  54. 54. 1.- COMPARATIVE ANATOMY HOMOLOGOUS ORGANS: share a common structure because they have a common origin, though they may have evolved to perform different functions
  55. 55. VESTIGIAL ORGANS: organs that have lost their function.
  56. 56. ANALOGOUS ORGANS: organs that have similar functions but have a different structure (they have different origins)
  57. 57. 2.- EMBRYOLOGY The first stages of development of different organisms show many similarities.
  58. 58. 3.- PALEONTOLOGY: fossils Archaeopteryx shows intermediate features between reptiles and birds.
  59. 59. 4.- BIOGEOGRAPHY:
  60. 60. 5.- MOLECULAR BIOLOGY:
  62. 62. NATURAL SELECTION (NS) preserves favourable variation and removes unfavourable NS depends on the ENVIRONMENT NS needs TIME to produce changes NS acts GRADUALLY NS HAS NO GOAL: IT ACTS BLINDLY
  63. 63. Other sources of variability: - Genetic RECOMBINATION - Random FERTILIZATION
  64. 64. Peppered moth in Manchester
  65. 65. WHAT IS A SPECIES? A group of individuals with similar features that can interbreed (exchange genes) and produce a fertile offspring.
  66. 66. How are new species formed?: SPECIATION A BARRIER splits a population Gradual accumulation of small changes TIME Genetic isolation
  67. 67. Two mechanisms of speciation:
  68. 68. Isolation: - geographical - ecological - behavioural - genetic isolation - reproductive isolation
  69. 69. HUMAN EVOLUTION Our place among the species. We often make the mistake of thinking humans are at the center of the biosphere or even the universe. This is not the case. We are only one of over a million known species living on this planet, and it’s estimated that we’ve only discovered a fraction of the total number in existence.
  70. 70. Australopithecus, Homo habilis, Homo erectus, Homo heidelbergensis, Homo neanderthalensis Homo sapiens
  72. 72. BIPEDALISM