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. Darwin’s Ideas BEFORE his Voyage. Fixity or Immutability of Species
Darwin’s Descent with modification
Logic of Darwin’s theory
Where are the Galapagos Islands?
What kind of islands are they?
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
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 migrationBio-geographic Evidence from the Voyage
Two Kinds of Islands
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
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.Bio-geographic Evidence from the Voyage
The ONLY Figure in
The Origin of Species.
It is THE most
important Figure for
you to understand in
regard to this class.
Darwin’s Answer: When did the two species last share a common ancestor?
1, 2, and 3
A NODE is the common ancestor of all species on the branches that radiate from the node.
Closely related species share a more recent common ancestor (MRCA) than more distantly related species
1 and 2
1 and 3
2 and 3
". . . 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.
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).
Voyage of the Beagle
The Growth of Biological Thought
The mechanism causing adaptation is Natural Selection