1. EVOLUTION?
Modern Clues
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2. Evidence: Fossils Fossils show: Life has changed over time
More than 99% of all organisms that have ever lived are extinct now
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3. What can fossils tell us?
Provide models of what life may have looked like
Provide clues to lifestyle:
Family groups
Foods
Environment
Provide clues to evolutionary relationships among organisms
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4. Gaps in the Fossil Record
Incomplete record
Most organisms do NOT become fossils
We have NOT found all fossils
What we DO know:
Simpler forms of life existed early in Earth’s history
More complex forms of life appeared later
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6. Evidence: Embryology Embryo: the earliest growth stage of an organism
Embryology: the study of these early growth stages
Human embryo at four weeks:
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7. Vertebrate Embryos
The embryos of fish, reptiles, birds and mammals are similar (tail, gills or gill slits)
This suggests an evolutionary relationship: common ancestors
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8. Evidence: Homologous Structures
Populations evolve to adapt to a particular environment
Structures with similar origins are homologous
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9. Homology= similar origin but adapted for different functions
Analogy+= similar functions, but evolved from different origins
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10. Evidence: Vestigial Structures
Vestigial structures: structures that no longer seem to have a function
Manatees, snakes, and whales no longer have legs, but still have hip bones
Vestigial structures may once have functioned in an ancestor
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11. Evidence: DNA Recall: Found in genes, located on chromosomes
Scientists compare DNA to identify similarities between organisms
By looking at DNA, scientists can determine how closely related two organisms are
Example: DNA studies that dogs are the closest relatives of bears
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13. Evidence: DNA Humans 23 pairs of chromosomes Apes:
24 pairs of chromosomes—but when two of an ape’s chromosomes are laid end-to-end, a match for human chromosome number 2 is found
Humans and apes make similar proteins, such as hemoglobin, the oxygen-carrying protein in red blood cells
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14. Putting it All Together
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