evolution. charles darwin was a british naturalist (a person who studies the natural world). he came...
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EvolutionEvolution
Charles Darwin
• Was a British Naturalist (a person who studies the natural world).
• He came up with theory of Evolution by Natural Selection while on an observation trip aboard the HMS Beagle.
The Beagle’s Journey• Visited South America
and the Galapagos Islands (among other places) (1835)
• Darwin saw many plants and animals on the Galapagos Islands that were similar to ones found in South America, but not the same
The Galapagos Islands
Darwin’s Observations
Turn and talk to your group. What observations can you make about this Iguana found on the mainland of South America?
Darwin’s ObservationsMainland:
– Iguana’s with small claws to climb trees
– Iguana’s green in color to blend in with leaves
– Iguana’s don’t have webbed feet
Darwin’s Observations
Now, turn and talk to your group again. What observations can you make about this Iguana found on the Galapagos Islands? How does it compare to the South American Iguana?
Galapagos:
– Iguana's with large claws to grip rocks
– Iguana’s gray in color to blend in with rocks
– Iguana’s have partially webbed feet
Darwin’s Observations
Why the difference?
• Based on Darwin’s observations, he theorized that a small number of different plant and animal species came to the Galapagos Islands from the mainland (South America).
• They started reproducing and eventually their offspring became different from their mainland relatives.
Darwin’s Hypothesis
• On his journey home, thought about his observations
• Darwin’s Hypothesis-separate new species may have come from one original ancestor
Darwin’s Theory of Evolution
• Darwin thought that the species gradually changed over many generations and became better adapted to the new conditions.– Species-a group of similar organisms
that can mate with each other and produce fertile offspring
– Evolution-the gradual change in a species over time
What is the difference between a theory and a law?
• A theory is a scientific explanation of an observation. Unlike laws, theories actually explain why things are the way they are.
• A scientific law is a description of an observation. Newton’s Laws of motion are good examples. Those laws describe forces in physics, but they do not explain why they are that way.
Selection• Natural Selection- process by which
individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. “Survival of the Fittest”
• Artificial Selection- humans decide which traits in a species are desirable and breed individuals with those traits (aka Selective Breeding)
Evolution by Natural Selection• Over a long period of time, natural
selection can lead to evolution. Helpful traits are passed down from parents to offspring while unfavorable traits are not.
• Over many generations, the species can change to better suit their environment.
Factors that affect Natural Selection
1. Variation
2. Overproduction
3. Competition
1. Variations-differences between individuals of the same species. Variations can be passed down from parents to offspring. For example, some newly hatched turtles can swim faster than other turtles. These faster turtles will survive to pass their traits on to offspring who will also be fast.
The 3 Factors in Natural Selection
Some variations allow members of a species to survive and reproduce better than others.
The 3 Factors in Natural Selection
The 3 Factors in Natural Selection2. Overproduction-organisms produce
more offspring than can survive. There are not enough resources for all to survive so only those that have traits best suited for survival will live to reproduce. Their offspring will inherit those traits.
3. Competition-organisms of the same species must compete for resources. For example, some might not find enough to eat. Those that are successful in competition will live reproduce and pass their traits to their offspring.
The 3 Factors in Natural Selection
• Some variations make individuals better adapted to their environment so when they reproduce, their offspring may inherit those traits.
• The offspring will be better suited for the environment and continue to pass the traits on.
• After many generations, more members of the species may have the helpful trait. In effect, the environment has “selected” organisms with helpful traits to be the parents of the next generation.
In Summary
Evidence of Evolution
• Fossil Record
• DNA
• Homologous Body Structures
• Similarities in Early Development
• Vestigial Organs
DNA
• Organisms that have close relatives have similar DNA–The more similar the DNA, the
more closely related the species are
• Scientists have even found ways to get DNA from some fossils
Homologous Body Structures
• Homologous structures-similar structures that are inherited from a common ancestor
• When organisms have homologous structures, it means they evolved from a common relative
• Analogous structures-similar structures that evolved separately, not from a common ancestor.
A shows that that sharks and lizards have a common ancestor who had limbs like they have now.
B shows that even thought the octopus has a similar kind of limb as sharks and lizards, it is an analogous structure since the octopus doesn’t share a common ancestor with the shark and lizard.
A B
Limb=arm or leg
Tetrapod=an organism with 4 limbs
Similarities in Early Development• Scientists look at early
development of different organisms to see if they are similar
Vestigial Organs
• A body part that doesn’t seem to have any function at this time– Ex-appendix, tailbone and wisdom teeth in
humans, pelvic bone in whales, wings on ostrich and emus
What does it all mean?• Scientists have combined evidence from
fossils, DNA, similar structures, etc to determine evolutionary relationships among species
• Branching Tree- a diagram that shows how scientists think different groups of organisms are related
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