When Is a Flipper a Wing? All living things are related. Some relationships are easy to see— your pet cat may not roar like a lion, but it clearly resembles one. Other relationships are less obvious. Section 15-3. Interest Grabber.
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2. Give one example for each group, and then fill in the information for that example. For Legs, write in the number of legs that each animal has. Do animals with fins have legs? Do animals with wings have legs? If so, how many?
3. Can you tell from your table if a fish is more closely related to a bird or to an amphibian? Explain your answer.Interest Grabber continued
After Darwin’s journeys he wrote and published a book called On the Origin of Species
Thomas Malthus—(Essay on the Principle of Population, 1798)
plants and animals produce more offspring than can survive.
human overpopulation would lead to decreasing living standards if left unchecked.
Charles Lyell (1797-1875)
Assumed natural forces in past same as today (erosion, sedimentation, etc.)
Uniformitarianism (idea originally proposed by James Hutton but popularized by Lyell)
"In October 1838, that is, fifteen months after I had begun my systematic inquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long- continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The results of this would be the formation of a new species. Here, then I had at last got a theory by which to work".Charles Darwin, from his autobiography. (1876)Objective: Summarize Darwin’s theory of evolution by natural selection
"I am well aware that this doctrine of natural selection . . . is open to the same objections which were at first urged against Sir Charles Lyell’s noble views on ‘the modern changes of the earth, as illustrative of geology;’ but we now very seldom hear the action, for instance, of the coast waves, called a trifling and insignificant cause, when applied to the excavation of gigantic valleys or the formation of the longest lines of inland cliffs. Natural selection can act only by the preservation and accumulation of infinitesimally small inherited modifications, each profitable to the preserved being; and as modern geology has almost banished such views as the excavation of a great valley by a single diluvial wave, so will natural selection, if it be a true principle, banish the belief of the continued creation of new organic beings, or of any great and sudden modification in their structure.” Charles Darwin, from the Origin of Species, 1859
Darwin proposed that as populations grew that there would be a struggle for existence
Some members of a species have characteristics that enable them to survive, produce more offspring than others, and pass these characteristics on.
(Species—a group of similar organisms capable of reproducing with one another).
Fitness—the relative ability of an organism to survive and transmit its genes to the next generation.
Adaptation—a characteristic that increases the chances an organism will survive and reproduce in its environment.
Note: It is species that evolve, not individuals.
Gene pool—the entire collection of genes among a population of organisms.
Population genetics—the study of gene pools and their changes.
Populations tend to be constant
Naturally occurring variations—small differences between members of a species
If more offspring are born, yet population is constant, then there is competition for food, water, light, etc.
Some variations are helpful and others aren’t. Natural selection eliminates those that aren’t.
Good variations are adaptationsNatural Selection
Darwin proposed that over long periods of time organisms developed different structures to adapt to different environments
Archaeopteryx indicates that birds probably evolved from reptiles.
Artificial selection (domestication)
Antibiotic resistant bacteria
Anol Lizards in the Bahamas, Etc.
Homologous structures—2 organisms w/parts that have similar organization that is functionally unnecessary (meaning the similarity is unnecessary but the trait in question may be, and usually is, functional).
Indicates a common ancestor
May or may not have similar function today
Whale fin & our forelimbObservations/Experiments that Support Natural Selection
Did not come from a recent common ancestor
Whale vs. shark fin
Insect vs. bird wing
Vestigial structures—parts that are no longer useful.
Snakes with nerves to their “legs”
Birds have genes that code for a reptilian mouth and tail.
Variations—within a species there are variations—hair, color, height, etc.
Inheritance of variations
Not all survive. Struggle for existence. Competition for resources.
Survival of the fittest, the best adapted.5 Main Assumptions of Darwin