Evidence for Evolution
Unit 7, lesson 2
Evidence for Evolution:
 Fossil Record
 Adaptations
 Anatomy and development
 Molecular Evidence
Fossil Evidence
• Provides a record of early life and evolutionary change
• The earth’s layers show a time scale of species and
when they appeared on earth (and when they died
out)
• Lower layers = older
• Shows the order in which species appeared
• Shows transitional fossils, or “in-between” species
• Shows similarities between ancient and modern
species
Adaptations:
 Adaptation: any variation that helps an organism to
survive in its environment
 Example: thorns, distinctive coloring, camouflage
 Darwin’s theory of Evolution through Natural
Selection explains HOW adaptations may develop
Comparative Anatomy
 Homologous structures
 Analogous structures
 Vestigial structures
 Transitional anatomy
Homologous Structures
• Structures with a common origin, similar structures
regardless of function
ex. Limbs of crocodiles, The flippers of whales, and the wings of
birds
All forelimbs of vertebrates have the same pattern of bones
• Suggest a common ancestry
Analogous Structures
 Structures without common evolutionary origin
 Similar in FUNCTION, but not STRUCTURE
 Can develop when two organisms have the same
environment
 Examples: insect and bird wings
Analogous Structures
Similar structures that serve the same function but
evolved SEPARATELY
They are similar because they live in similar
environments, not because of a common ancestor
Vestigial Structures
 Structure that no longer has a use in an organism
 Why are they there if they have no function?
 Leftover from ancestors
 Example: pelvic bones in whales, eyes on the blind
mole-rat
• Vestigial Structures– these are organs or parts
that seem to have no function
Whales have pelvic bones that do not attach to legs
Vestigial Structures
 Humans have a “tail bone” and wisdom teeth
Transitional Features
 Tiktaalik
 https://www.youtube.com/watch?v=T2vKlEUX7DI
Development (embryology)
 Embryo- earliest stage of growth and development in
plants and animals
 It’s the shared features in the young embryos that
suggest evolution from a distant common ancestor in
fish, reptiles, birds, and mammals
Embryological Development
Embryos of different species develop in almost identical
ways.
Molecular Evidence
 Molecules in a species with a common ancestor
share certain amino acid sequences
 There are also biochemical patterns in proteins,
DNA, and RNA among species thought to have
shared a common ancestor
 Organisms that are more recently related have more
similarities
When comparing the DNA of one species to another,
more similarities are found in species that are more
closely related. Lions and Tigers have a common
ancestor.
Lion photo credit: ucumari Tiger photo credit: digitalART2
Crash Course: Speciation
https://www.youtube.com/watch?v=2oKlK
mrbLoU&list=PL3EED4C1D684D3ADF&ind
ex=15
Your turn…
 WB page 176, # 1-5