Lecture 3

• Charles Darwin


  • Wealthy son of an English doctor
  • Studied medicine in Edinburgh, but thought lectures were dull and surgeries (w/o anaesthetic) were brutal; dropped out
  • Earned a BA in Theology at Cambridge University
  • Believed in the literal truth of the Bible when young
  • Charmed and convinced by Paley's watchmaker argument
  • Passionate about natural history
  • Learned taxidermy under teacher John Edmonstone (a former British-Guyanese slave)
• The Voyage of the Beagle

  • At age 22, Darwin was asked to join the second voyage of HMS Beagle as gentleman companion to Captain FitzRoy (and unofficial naturalist)
  • Voyage: Dec. 27, 1831 – Oct. 2, 1836
  • Spent years exploring South American coast
  • Stopped at Galapagos Islands off Ecuador, then New Zealand and Australia
• Darwin on the Voyage of the Beagle

  • Got seasick easily and spent as much time on land as possible
  • Became an accomplished naturalist
  • Recorded many observations
  • Collected many specimens (incl. fossils, barnacles)
  • Used his taxidermy skills to preserve birds (etc.)
  • Became deeply interested in Geology
  • Observed rock layers
  • Experienced an earthquake in Concepcion, Chile that lifted the shoreline by several feet (Feb. 20, 1835; M8.0–8.5)
  • Became a dedicated "Lyellian"
• Charles Lyell


  • Published Principles of Geology (1830–1833)
  • Popularized Hutton's gradualism and uniformitarianism
  • Darwin received 1st volume of Principles of Geology from Captain FitzRoy on the Beagle
  • Deeply influenced Darwin; Darwin developed a uniformitarian hypothesis of coral reef formation that proved correct
  • Darwin received 2nd volume of Principles of Geology while in South America
  • Lyell attacked Lamarckism and the concept of evolution generally
  • Darwin later shared his ideas about evolution with Lyell prior to publication
  • Lyell became one of Darwin's most trusted colleagues
• By 1835*, Darwin had figured out how coral reefs form: gradually

  
• Fringing reef


  Forms in shallow water around a volcanic island
• Barrier reef


  Island subsides and reef grows upward, creating a barrier reef
• Atoll


  Island subsides below the surface, leaving an atoll
• Remote archipelagos, like the Galapagos Islands, have been called "evolution's workshops"
• Water between islands is a barrier to gene flow between populations; facilitates speciation
• Each island may have its own endemic flora and fauna
• Archipelagos may have many endemic species because of adaptive radiation
• Uninhabited islands have many unoccupied niches
• Descendants of early-arriving species may diverge and adapt to fill those different niches
• The Galapagos Islands


  • Formed by volcanism starting 4mya; they move over a volcanic hotspot: old islands in east and young islands in west provide a variety of habitats
  • ~1000 km from the coast of Ecuador, at the intersection of two major trade winds and three major currents
  • Land area = 8010 km2; for their size, among the most biologically diverse places on earth
  • Windborne seeds, insects, birds, etc.
  • Iguanas, tortoises, penguins, crabs, etc.

  
• Darwin in the Galapagos


  • Arrived on Sept. 16, 1835
  • Spent ~5 weeks there
  • Left on October 20, 1835
  • Visited several islands, incl. San Cristobal, Floreana, Isabela, and Santiago

  
• Presence of different tortoises and mockingbirds on different islands made Darwin consider the possibility that species could evolve

  
• For now, Darwin rejected this possibility and considered them only as varieties
• The importance of Darwin's finches to his conversion is often exaggerated
• While in the Galapagos, Darwin did not know that "Darwin's finches" were all finches
• Realized their significance only after returning to England
• Darwin's conversion


  • Based on three lines of evidence: diversity of many groups (e.g., mockingbirds, finches, tortoises) across different Galapagos Islands, similarity of Galapagos species to nearby mainland species, and fossil succession in rock strata
  • By March 1837, Darwin believed that species were not immutable, but he had no mechanism for change
• Gentleman scientist


  • Darwin's family wealth allowed him to dedicate himself to Science
  • Started amassing evidence for evolution and thinking about its causes
• Thomas Malthus


  • Argued that human population growth is exponential, but growth of the food supply is linear
  • Therefore, unchecked population growth causes famine
• Darwin's real aha! moment: natural selection is the mechanism of evolutionary change
• The Voyage of the Beagle


  • Elected Fellow of the Royal Society in 1839
  • Published Journal and Remarks in 1839, now called The Voyage of the Beagle
  • Highly regarded as travelogue and natural history literature
  • Does not explicitly mention evolution
  • In 1844, Darwin wrote an essay describing his theory of evolution… He never published it in full.
• Vestiges of the Natural History of Creation


  • Controversial book published in 1844, written anonymously by geologist Robert Chambers
  • Presented a difficult-to-understand theory of evolution based on an unfolding of a preordained plan for the universe
  • International bestseller; read by Queen Victoria, Lincoln, etc.
  • Enjoyed by the public; criticized by scientists and clergy
  • Darwin thought it might open minds to evolution in the long run, but for now the time was not right
  • Darwin did not announce his theory for ~15 more years
  • Told only a select few, esp. Charles Lyell and botanist Joseph Hooker
• Darwin's research on barnacles


  • From 1846 to 1854, Darwin studied barnacles
  • Became the world's leading expert on barnacles
  • Contributed to his theory of evolution in many ways: developed experience in comparative anatomy, developed his sense of variation within & among species, observed a gradation of forms that suggested common ancestry and gradual change over time, further established his reputation as a naturalist
• Later experiments addressed: how long could seeds remain in saltwater and still germinate, what if they were inside a dead bird, what about lizard eggs, how long do they float, will they still hatch, how many snails can cling to the feet of a duck, can they be transported that way
• Darwin did not announce his theory for ~15 more years after the time was not right to open minds to evolution
• Darwin told only a select few about his theory, especially Charles Lyell and botanist Joseph Hooker
• Darwin's research on barnacles


  1. Studied barnacles from 1846 to 1854

  2. Became the world's leading expert on barnacles

  3. Developed experience in comparative anatomy (homology)

  4. Developed his sense of variation within & among species

  5. Observed a gradation of forms that suggested common ancestry and gradual change over time

  6. Further established his reputation as a naturalist
• Later experiments by Darwin

  1. How long could seeds remain in saltwater and still germinate?

  2. What if they were inside a dead bird?

  3. What about lizard eggs? How long do they float? Will they still hatch?

  4. How many snails can cling to the feet of a duck? Can they still cling while the duck is flying?
• In 1854, Darwin started preparing a book to be called Natural Selection but never finished it
• Darwin's research on pigeons

  1. Began breeding pigeons in 1855

  2. Wanted to determine how artificial selection (selective breeding by humans) could produce a wide range of varieties

  3. Correctly determined that all domestic pigeon breeds are descended from wild rock dove

  4. Modified by artificial selection over many generations
• Alfred Russel Wallace


  Naturalist who described the idea of natural selection independently of Darwin, while bedridden with malaria
• Darwin suggested his and Wallace's idea be presented (and published) jointly at an 1858 meeting of the Linnean Society, but the presentation and publication attracted little attention
• On the Origin of Species (1859)

  • Instant classic; structured as "one long argument" for evolution
  • Supported by evidence from hybrid sterility, comparative anatomy, geographical distributions, fossil succession, and evolution of instincts
  • Contains only one coy line about human evolution
• Charles Darwin, 1859: 'It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us.'
• Lamarck's view on adaptation


  Traits of individuals change within a generation due to use and disuse, and changes are passed on to the next generation because of inheritance of acquired characteristics