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Evidence of Evolution
1. Fossil Record2. Homologous Body structures
3. Similarities in Embryology 4. Biochemical Evidence
Evidence of Evolution:The Fossil Record
• Fossil record provides evidence that living things have evolved
• Fossils show the history of life on earth and how different groups of organisms have changed over time
Relative vs. Absolute Dating
Relative Dating
• Can determine a fossil’s relative age
• Performed by estimating fossil age compared with that of other fossils
• Drawbacks – provides no info about age in years
Absolute Dating
• Can determine the absolute age in numbers
• Is performed by radioactive dating – based on the amount of remaining radioactive isotopes remain
• Drawbacks - part of the fossil is destroyed during the test
– A half-life is the amount of time it takes for half of the isotope to decay.
• Radiometric dating uses decay of unstable isotopes.
– Isotopes are atoms of an element that differ in their number of neutrons.
Primate Fossils
Australopithecus Homo erectus Homo sapien
Primate Bone Structure
Evidence of Evolution:Homologous Body Structures
– Structures that have different mature forms but develop from the same embryonic tissues
Ex: Wing of bat, human arm, leg of turtle
Turtle
Alligator
Bird
Evidence of Evolution:Homologous Structures
• Features that are similar in structure but appear in different organisms and have different functions.
• Strong evidence for common ancestor.• Ex: forelimbs of humans, bats and moles.
Human hand Bat wingMole foot
Analogous Structures• Structures that perform a similar
function.• Not evidence of common ancestry.
Vestigial Structures• Remnants of organs or structures that had a
function in an early ancestor.• Ex: Ostrich wings, used for balance but not
flight• Ex: Humans’ appendix
Evidence of Evolution:Similarities in Embryology
In their early stages of development, chickens,
turtles and rats look similar, providing
evidence that they shared a common
ancestry.
Embryological Development
Evidence of Evolution:Biochemical Similarities
• Scientists study nucleotide sequences in DNA and proteins in different organisms to determine ancestry.
• If the organisms are closely related they will have similar sequences of nucleotides in their DNA and arrangement of amino acids in proteins.
Evidence of Evolution:Biochemical Similarities
Organism Amino Acid Differences
Organism Amino Acid Differences
Human beta chain 0 Mouse 27
Gorilla 1 Kangaroo 38
Rhesus monkey 8 Chicken 45
Dog 15 Frog 67
Cow 25 Soy bean 124
The more similar the amino acid sequence, the more closely related the organisms are.