Evidence for Evolution

Fossil Record

• Shows gradual changes in organisms over time

• Has some major gaps– Caused by:

• Conditions have to be just right for fossils to form• soft-bodied organisms can’t be fossilized (they just

get squished)• many fossils have been scattered and aren’t intact• some fossils destroyed by plate tectonics

Evolution of the Camel

Evolution of the horse

Comparative Anatomy

• Homologous Structures: body structures with a common embryological origin

• Example: many animals have forelimbs with similar structures– Derived from the same structures in the

embryo– Suggests a common origin

• Analogous Structures: different structures in different groups of organisms undergo modifications to serve similar functions

• Example: wings of bats, birds, and butterflies

• These do not have a common evolutionary origin

Vestigial Structures

• Body parts which are considered evolutionary “leftovers”

• They are present but non-functional– Had a function in some ancient ancestor

• Examples in humans:– Tailbone – Shriveled up third eyelid– Goosebumps

• Pelvic bones in whales• Eyes in blind salamanders

Comparative Embryology

• Developing embryos of organisms from fish to humans look almost identical

Fishsalamander

tortoise chicken pigcow

rabbithuman

Biochemistry

• ALL organisms have the same DNA bases of T, A, G, C

• Organisms with more similar DNA are more closely related