Evidence for Evolution

Five main examples of Evidence for Evolution Fossils Geographical Distribution Embryology Comparative Anatomy Molecular and Genetic

#1 Fossil Evidence Fossils The oldest fossil on record is estimated 3.7 billion years old Fossils in older layers are more primitive than those in the upper layers. It can be easy to see the progression of life from ancient fossils to modern organisms.

Types of Fossils Permineralization occurs when minerals carried by water are deposited around a hard structure A natural cast forms when flowing water removes all of the original tissue, leaving an impression.

Types of Fossils Amber-preserved fossils are organisms that become trapped in tree sap that hardens after the tree is buried.

Types of Fossils Impressions are imprints left in sedimentary rock Preserved remains form when an entire organism becomes encased in material such as ice, ash, tar …

Why don’t all organisms get fossilized? Some organisms’ soft body types just don’t fossilize well (fungus, jellyfish, etc.) Very specific conditions are required for fossils to form; many places on Earth are geographically unsuitable for fossils to form Scientists are still finding new fossils everyday; we have not found every fossil yet!

#2 Geographical Distribution similar species are found in similar environments or the same area Island species most closely resemble nearest mainland species Populations can show variation from one island to another

#2 Geographical Distribution The same fossil species can be found across continents The continents were all once connected into the super-continent Pangea

#3 Embryology Embryos (early developmental stage) show evidence of evolution Some related species have almost identical larvae, but different adult body forms All vertebrates have similar embryos which differentiate as the specific organism grows up Larva Adult barnacle Adult crab

Which is the human?

How about now? Can you tell yet?

#3 Embryology Vertebrates all share gill slits and a tail in their early embryo stage; this is evidence they share a common ancestor (a fish)

#4 Comparative Anatomy The study of anatomy provides evidence of evolution; we can see the similarities in body structure of related organisms Homologous structures are similar in structure but different in function. Homologous structures ARE EVIDENCE of a common ancestor.

Homologous Structures ARM LEG Wing Flipper grasping walking swimming flight

#4 Comparative Anatomy Analogous structures are similar in function but differ in structure Analogous structures DO NOT show common ancestry Fly wing Bat wing

Structural patterns are clues to the history of a species. Vestigial structures are remnants of organs or structures that had a function in an early ancestor. Examples include ostrich wings, human appendix and wisdom teeth, whale and snake pelvis/hind legs

Pythons have tiny claws where their ancestors had legs

#5 Molecular and Genetic Evidence AKA Biochemical Evidence Two closely-related organisms will have similar DNA, RNA, and protein (amino acid) sequences. This is the best evidence for evolution because it is an exact measure of how genetically similar two organisms are.