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Slide 2 of 20
Galapagos Islands
Darwin visited the Galapagos Islands He formed his ideas about natural
selection here Why were the Galapagos Islands a
good place to study natural patterns?
Variation – difference in physical traits of an individual from those of the other members in the group
Darwin took note of the variation of organisms via each island in the Galapagos
Slide 3 of 20
Different environments
Long necked and legged tortoises lived in areas with mostly tall plants.
Tortoises with a short neck and legs, lived in areas with short plants and mosses.
Animals could adapt to their environment?
Slide 4 of 20
Adaptation
Adaptation – feature that allows an organism to better survive in its environment
Adaptations can lead to a genetic change in a population over time
Evolution – genetic change in a population over time
So adaptations can lead to ______ ?
Slide 5 of 20
Ancient Earth?
Darwin found fossil evidence of ancient & extinct organisms that were similar but different than currently living (extant) forms.
Slide 7 of 20
Selection
Darwin observed that domesticated plants and animals displayed variation that was not found in their wild counterparts
Through selection of animals with particular traits, breeders could produce a great amount of diversity
Artificial selection – humans select for certain traits, and preferentially breed those animals in possession of those traits Called artificial selection since humans are selecting for
certain traits that they deem desirable
Slide 8 of 20
Heritability
In order for a trait to be selected for, artificial or natural, trait must be inherited
Heritability – the ability of a trait to be passed down from one generation to the next
Slide 9 of 20
Natural Selection
Natural Selection – mechanism by which individuals that have inherited favorable adaptations produce MORE offspring on average than do other individuals
Environment is the selective agent
Characters are selected only if they confer some advantage to those who have it
Slide 10 of 20
Conditions for Natural Selection
Struggle for survival Resources are limited
Space, food, mating opportunities Wants are Unlimited
Organisms can produce more offspring than the environment can provide for
Certain adaptations seemed well-suited for their environment
Slide 11 of 20
4 Principles for Theory of Natural Selection
1. Variation the heritable differences are the basis for natural selection
2. Overpopulation If the population is supported by the environment, no selection
will occur
3. Adaptation Certain individuals have favorable variation that enables them
to be better suited to their environment
4. Descent with Modification Natural selection will result in populations that are better suited
to survival and reproduction in an environment
Slide 13 of 20
Imperfect Organisms
Why are organisms not perfectly adapted to their environment?
Natural selection works on EXISTING variation
Natural selection can only modify what is there, so perfect structures are not always possible
Could a human ever be able to lift 18 tons (36,000 pounds)?
Could a human ever be able to develop gills for underwater existence?
Slide 14 of 20
Evidence for Evolution
Fossils Okay
Biogeography Good
Embryology Excellent
Anatomy Excellent
Genomics
Slide 15 of 20
Fossils provide evidence of evolution.
• Fossils in older layers are more primitive than those in the upper layers.
Slide 16 of 20
The study of geography provides evidence of evolution.
– island species most closely resemble nearest mainland species– populations can show variation from one island to another
Slide 17 of 20
Embryology provides evidence of evolution.
Larva
Adult barnacleAdult crab
– identical larvae, different adult body forms– similar embryos, diverse organisms
Slide 19 of 20
The study of anatomy provides evidence of evolution.
Human hand Bat wingMole foot
– Homologous structures are similar in structure but different in function.
– Homologous structures are evidence of a common ancestor.
Slide 20 of 20
Human hand
Bat wing
Mole foot
Fly wing
Analogous structures are not evidence of a common ancestor.
Analogous structures have a similar function.
Slide 21 of 20
• Vestigial structures are remnants of organs or structures that had a function in an early ancestor.
• Ostrich wings are examples of vestigial structures.
Vestigial Structures