2. Evolution by Natural Selection

3. "Nothing in biology makes sense except in the light of evolution."
Theodosius Dobzhansky: Integrating Genetics and Evolution
Theodosius Dobzhansky, a Russian geneticist who moved to the United States, provided laboratory evidence for natural selection and variation where previously there had been only field observation. Dobzhansky's work with Drosophila, or fruit flies, provided new evidence that supported Darwin's theory that natural selection, acting on genetic variation in populations, is a driving force in evolution.
-- Theodosius Dobzhansky March 1973
Geneticist, Columbia University
( )

4. TINTORETTO The Creation of the Animals 1550

5. Life’s Natural History is a record of Successions & Extinctions
mya
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Ediacaran
Precambrian,
Proterozoic,
&
Archarozoic
1.5
Plants
Birds 63
Mammals
135
Reptiles
Seed Plants
Flowering
Amphibians
Insects
180
Dinosaurs
Teleost Fish
Land Plants
225
Jawless Fish
Molluscs
Arthropods
Chordates
Multicellular Animals
280
Green Algae
Photosynthetic Bacteria
350
Anaerobic Bacteria
400
430
500
570
700
4500
Life’s Natural History is a record of Successions & Extinctions

6. Life has changed & changed the Earth
Living creatures have changed Earth’s environment, making other life possible

7. Mylodon (left) Giant ground sloth (extinct)
Modern sloth (right)
This wonderful relationship in the same continent between the dead and the living will…throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts.

8. Just a theory?
Evolution Definition #1: life on Earth changed over time
Evolution Definition #2: life on Earth changes by means of natural selection
Scientific fact
Scientific theory = explanation of why natural world is the way it is based on LOTS of scientific evidence

9. In historical context Darwin did not originate the idea of evolution
Geologic theories of Earth’s age & history cleared the path for evolutionary biologists
…immeasurable time…

10. LaMarck Organisms adapted to their environments through
Use & disuse of body parts lost parts because they did not use them or gained/increased body parts if needed or used often
missing eyes & digestive system of the tapeworm
muscles of a blacksmith or large ears of a night-flying bat
Transmittance of acquired characteristics to next generation
Lamarck noted how well-adapted organisms were to their environments, and believed that fossils could be understood as less perfect forms which had perished in the struggle for increasing perfection. He explained adaptation as a result of change caused by environmental pressures.

11. Charles Darwin 1809-1882 British naturalist
Proposed the idea of evolution by natural selection
Collected clear evidence to support his ideas
What did Darwin say?
What evidence supports Evolution by Natural Selection?
What impact did Evolution have on biology?

12. Voyage of the HMS Beagle
Travels around the world
makes many observations of natural world
main mission of the Beagle was to chart South American coastline
Robert Fitzroy
After graduation Darwin was recommended to be the conversation companion to Captain Robert FitzRoy, preparing the survey ship Beagle for a voyage around the world.
FitzRoy chose Darwin because of his education, his similar social class, and similar age as the captain.
Darwin noted that the plants and animals of South America were very distinct from those of Europe

13. Galapagos
Of relatively recent volcanic origin most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland.
500 miles west of mainland

14. Unique species
Show Campbell videos!!!

15. The Birds… Galápagos birds One particular group…
22 of the 29 species of birds on the Galapagos are endemic
found only on these islands
collected specimens of all
One particular group…
Darwin was amazed to find out they were all finches
14 species
but only one species on South American mainland
500 miles away

16. Correlation of species to food source
Seed eaters
Flower eaters
Insect eaters
Rapid speciation: new species filling new niches, because they inherited successful adaptations.
Adaptive radiation

17. Darwin’s finches Darwin’s conclusions
small populations of original South American finches reached islands
variation in beaks enabled some to obtain food successfully in the different environments
over many generations, the populations of finches changed anatomically & behaviorally
accumulation of advantageous traits
emergence of different species

18. Darwin’s finches Finches with beak differences that allowed them to…
successfully compete
successfully feed
successfully reproduce
pass successful traits onto their offspring

19. Correlation of species to food source
Whoa, Turtles, too!

20. Many islands also show distinct local variations in tortoise morphology…
…perhaps these are the first steps in the splitting of one species into several?

21. “On the Origin of Species by Means of Natural Selection”
Voyage:
November 24, 1859, Darwin published
“On the Origin of Species by Means of Natural Selection”

22. Essence of Darwin’s ideas
Variation exists in natural populations
(2) Many more offspring are born each season than can possibly survive to maturity
(3) As a result, there is a struggle for existence
- competition
(4) Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the average characteristics of the population
- adaptations
(5) Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species

23. Natural Selection
Darwin referred to all of these factors together as natural selection
variation
production of more offspring than can survive
competition
for food, for mates & nesting spots, to escape predators
differential survival based on traits
successful traits = adaptations

24. LaMarckian vs. Darwinian view
in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring
Darwin
longer-necked giraffes survive better & leave more offspring who inherit their long necks
genes 

25. Any Questions??