1. 1 Outline for Week 2 these notes represent 1/3 of the slides shown in class Darwin’s Descent with modification – Geological evidence – Bio-geographical evidence Logic of Darwin’s theory Virus Evolution

2. 2 Darwin’s Ideas BEFORE his Voyage Fixity or Immutability of Species – each species was a single, unchanging entity, separate from other species and constant in its fundamental, defining characteristics. Evolution or the Transformation of Species – was a speculative idea, espoused by some (including his grandfather, Erasmus Darwin) but with little evidence and no mechanism(s).

3. 3 Key insights from Lyell for Darwin Gradualism - weak forces acting over long periods could produce as large geological changes as catastrophic forces produce in a short period of time. Uniformitarianism - geologic processes acting today are similar to those occurring throughout Earth’s geological history. They account for all of Earth's geological features: “the present is the key to the past.”

4. 4 Isabela Darwin Wolf Pinta Marchena Genovesa Fernandia Santiago Bartolomé Råbida Pin zon Seymour Baltra Santa Cruz Santa Fe Tortuga Española San Cristobal Floreana EQUATOR Galåpagos Islands Galapagos Islands Where are the Galapagos Islands? What kind of islands are they?

5. 5 Bio-geographic Evidence from the Voyage Oceanic Islands Formed by Volcanoes. Far from Mainland. Each island had a unique group of species Species on young islands more similar to mainland species Descended from a colonizing ancestor with modification Unknown Mechanism Continental Islands Formed by breaking off from the Mainland. Near to Mainland. Species were a subset of those on the nearby mainland. Source of species, colonization from mainland. Recurrent migration Two Kinds of Islands Darwin’s Hypotheses

6. 6 Galapagos finches Differ in Beak Shape and Diet

7. 7 Darwin’s Hypothesis

8. 8 Hawaiian honeycreepers ≈ Galapagos Finches

9. 9 Bio-geographic Evidence from the Voyage South American Fossils Extant species resembled the fossils of S. A. more closely than fossils of Europe from the same strata. Extant Species Descended with modification from Fossil Species Unknown Mechanism European Fossils Extant species resembled the fossils of Europe more closely than fossils of S. A. from the same strata. Extant Species Descended with modification from Fossil Species Descent with modification Unknown Mechanism. Darwin’s Hypotheses

10. 10 Darwin’s Ideas after the Voyage Fixity or Immutability of Species: Unlikely. Evolution or the Transformation of Species: Likely – Much bio-geographic evidence but – No mechanism(s) to explain how or why species change.

11. 11 The ONLY Figure in The Origin of Species. It is THE most important Figure for you to understand in regard to this class.

12. 12 Darwin’s Theory of Descent with Modification Questions: How similar are two species? How many traits do the two species share? Darwin’s Answer: When did the two species last share a common ancestor? If they share a recent common ancestor, then the two species will be very similar and share many traits. If they share a distant common ancestor, then the two species will not be as similar and they will share few traits.

13. 13 Present: Living Descendants 1, 2, and 3 Are living Species today Past: Fossil Ancestors 1 2 3 Species Extinctions: branches that terminate before the Present

14. 14 Present: Living Descendants Past: Fossil Ancestors Extinctions: branches that terminate before the present A NODE is the common ancestor of all species on the branches that radiate from the node. 1 2 3

15. 15 Present: Living Descendants Past: Fossil Ancestors Extinctions: branches that terminate before the present Closely related species share a more recent common ancestor (MRCA) than more distantly related species 1 2 3 MRCA of 2 and 3 MRCA of 1 and 2 or 1 and 3

16. 16 Darwin knew his theory would be controversial "... We see this in the plainest manner by the fact that all the most eminent paleontologists, namely Cuvier, Owen, Agassiz, Barrande, Falconer, E. Forbes, &c., and all our greatest geologists, as Lyell, Murchison, Sedgwick, & c., have unanimously, often vehemently, maintained the immutability of species. But I have reason to believe that one great authority, Sir Charles Lyell, from further reflexion entertains grave doubts on this subject. I feel how rash it is to differ from these great authorities, to whom, with others, we owe all our knowledge. Those who think the natural geological record in any degree perfect, and who do not attach much weight to the facts and arguments of other kinds even in this volume, will undoubtedly at once reject my theory...." -Darwin, Charles On the Origin of Species, chapter 9.

17. 17 Darwin’s theory proposed to explain diversity by modification of descendants through time, BUT he desperately needed a mechanism to explain how modification occurred and caused the remarkable fit of organisms to their environments (i.e. adaptation). Extraordinary claims require extraordinary evidence

18. 18 Interesting Additional Readings Voyage of the Beagle Darwin’s Autobiography The Growth of Biological Thought

19. 19 The mechanism causing adaptation is Natural Selection