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Evolution by Natural Selection
Chapter 22 Darwin and Evolution by Natural Selection
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"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 ( )
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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.
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Glyptodont fossils are also unique to South America.
Succession of Types Armadillos are native to the Americas, with most species found in South America. Glyptodont fossils are also unique to South America. Why should extinct armadillo-like species & living armadillos be found on the same continent?
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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.
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LaMarck Organisms are adapted to their environments
through acquired traits change in their life time Use & Disuse organisms lost parts because they did not use them — like the missing eyes & digestive system of the tapeworm Perfection with Use & Need the constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith or the large ears of a night-flying bat transmit 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.
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In Historical Context…
Darwin did not originate the idea of evolution Geologic theories of Earth’s age & history cleared the path for evolutionary biologists AP Movie—Ch 22—Geologic Change Immeasurable time… Thank you Lyell!
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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?
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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
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Voyage of the HMS Beagle
Stopped in Galapagos Islands The origin of the fauna of the Galapagos, 900 km west of the South American coast, especially puzzled Darwin. On further study after his voyage, Darwin noted that while most of the animal species on the Galapagos lived nowhere else, they resembled species living on the South American mainland. It seemed that the islands had been colonized by plants and animals from the mainland that had then diversified on the different islands
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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
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Unique Species Show Campbell videos!!!
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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… at first, he paid little attention to a series of small birds some were woodpecker-like, some warbler-like, & some finch-like
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Darwin’s Finches Darwin was amazed learn they were all finches
14 species but only one species on South American mainland resembled the island finches 500 miles away all the birds had to originally come from mainland species… Darwin noted that the plants and animals of South America were very distinct from those of Europe. Organisms from temperate regions of South America were more similar to those from the tropics of South America than to those from temperate regions of Europe. Further, South American fossils more closely resembled modern species from that continent than those from Europe.
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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
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Darwin’s Finches Differences in beaks
associated with eating different foods adaptations to foods available on islands Warbler finch Woodpecker finch Small insectivorous tree finch Large insectivorous Vegetarian Cactus finch Sharp-beaked finch Small ground finch Medium ground finch Large ground Insect eaters Bud eater Seed eaters Cactus eater Warbler Tree finches Ground finches
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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
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Darwin’s Finches Seeing this gradation & diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species has been taken & modified for different ends.
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Darwin’s Finches Finches with beak differences that allowed them to…
successfully compete successfully feed successfully reproduce pass successful traits onto their offspring
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Correlation of species to food source
Whoa, Turtles, too!
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Many islands also show distinct local variations in tortoise morphology…
…perhaps these are the first steps in the splitting of one species into several?
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This is not just a process of the past… It is all around us today
Artificial Selection This is not just a process of the past… It is all around us today
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The raw genetic material is hidden there!
Selective Breeding The raw genetic material is hidden there!
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Lots of hidden variation comes out!
Selective Breeding Lots of hidden variation comes out! AP Movie—Ch 22: Artificial Selection
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A Reluctant Revolutionary
Returned to England in 1836 wrote papers describing his collections & observations long treatise on barnacles draft of his theory of species formation in 1844 instructed his wife to publish this essay upon his death reluctant to publish but didn’t want ideas to die with him
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And then came the letter….
Then, in 1858, Darwin received a letter that changed everything… Alfred Russel Wallace a young naturalist working in the East Indies, had written a short paper with a new theory. He asked Darwin to evaluate his theory and pass it along for publication.
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…and the time was ripe for the idea!
Your words have come true with a vengeance… I never saw a more striking coincidence…so all my originality, whatever it may amount to, will be smashed. To Wallace:
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November 24, 1859, Darwin published
Voyage: November 24, 1859, Darwin published “On the Origin of Species by Means of Natural Selection” AP Movie—Ch 22: 100 Greatest Discoveries—Natural Selection
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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 between members of a species (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 arise by survival! AP Link—Ch 22: NOVA critters (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…
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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 AP Link—Ch 22: NOVA—Evolution in Action
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The 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 (by genes, which he didn’t know about!)
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Any Questions??
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