Upload
duane-kennedy
View
215
Download
1
Tags:
Embed Size (px)
Citation preview
1
Outline for Week 2these 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
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
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
Isabela
Darwin
Wolf
Pinta
Marchena Genovesa
Fernandia
SantiagoBartolomé
RåbidaPin zon
SeymourBaltra
Santa Cruz
Santa Fe
Tortuga
Española
San Cristobal
Floreana
EQUATOR
GalåpagosIslands
Galapagos Islands
Where are the Galapagos Islands?
What kind of islands are they?
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
Galapagos finchesDiffer in Beak Shape and
Diet
7Darwin’s Hypothesis
8
Hawaiian honeycreepers ≈ Galapagos Finches
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
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
The ONLY Figure in The Origin of Species.
It is THE most important Figure for you to understand inregard to this class.
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
Present:Living
Descendants
1, 2, and 3 Are living
Species today
Past:Fossil
Ancestors
1
2
3
SpeciesExtinctions:
branches that terminate before
the Present
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
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
or1 and 3
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
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
Interesting Additional Readings
Voyage of the Beagle
Darwin’s Autobiography
The Growth of Biological Thought
19
The mechanism causing adaptation is Natural
Selection