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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

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Outline for week 2 these notes represent 1 3 of the slides shown in class

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


Darwin s ideas before his voyage

Darwin’s Ideas BEFOREhis 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 Transformationof Species

    • was a speculative idea, espoused by some (including his grandfather, Erasmus Darwin) but with little evidence and no mechanism(s).


Key insights from lyell for darwin

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.”


Outline for week 2 these notes represent 1 3 of the slides shown in class

Darwin

Wolf

Pinta

Genovesa

Marchena

Santiago

Bartolomé

Seymour

Råbida

Baltra

Pin zon

Fernandia

Santa Cruz

Santa Fe

Tortuga

San Cristobal

Española

Floreana

Where are the Galapagos Islands?

What kind of islands are they?

EQUATOR

Galåpagos

Islands

Isabela

Galapagos Islands


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

Bio-geographic Evidence from the Voyage

Two Kinds of Islands

Darwin’s Hypotheses


Galapagos finches differ in beak shape and diet

Galapagos finchesDiffer in Beak Shape andDiet


Darwin s hypothesis

Darwin’s Hypothesis


Hawaiian honeycreepers galapagos finches

Hawaiian honeycreepers ≈ Galapagos Finches


Bio geographic evidence from the voyage1

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.

Bio-geographic Evidence from the Voyage

Darwin’s Hypotheses


Darwin s ideas after the voyage

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.


Outline for week 2 these notes represent 1 3 of the slides shown in class

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 theory of descent with modification

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 recentcommon ancestor, then the two species will be very similar and share many traits.

  • If they share a distantcommon ancestor, then the two species will not be as similar and they will share few traits.


Outline for week 2 these notes represent 1 3 of the slides shown in class

Species

Extinctions:

branches that

terminate before

the Present

Present:

Living

Descendants

1, 2, and 3

Are living

Species today

Past:

Fossil

Ancestors

1

2

3


Outline for week 2 these notes represent 1 3 of the slides shown in class

Extinctions:

branches that

terminate before

the present

Present:

Living

Descendants

Past:

Fossil

Ancestors

A NODE is the common ancestor of all species on the branches that radiate from the node.

1

2

3


Outline for week 2 these notes represent 1 3 of the slides shown in class

Extinctions:

branches that

terminate before

the present

Present:

Living

Descendants

Past:

Fossil

Ancestors

Closely related species share a more recent common ancestor (MRCA) than more distantly related species

1

MRCA of

1 and 2

or

1 and 3

2

MRCA of

2 and 3

3


Darwin knew his theory would be controversial

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.


Outline for week 2 these notes represent 1 3 of the slides shown in class

Extraordinary claims require extraordinary evidence

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).


Interesting additional readings

Interesting Additional Readings

Voyage of the Beagle

Darwin’s Autobiography

The Growth of Biological Thought


Outline for week 2 these notes represent 1 3 of the slides shown in class

The mechanism causing adaptation is Natural Selection


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