Evidence For Evolution
1) Fossil Record2) Biogeography3) Homologous Structures4) Vestigial Structures 5) Comparative Embryology 6) Molecular Evidence 7) Imperfections of Adaptations
Rocks formed by layers (sediments) settling on top are called sedimentary.
Oldest Layers deposited first, oldest fossils
Newest LayersDeposited last, newest fossils
Geologists can determine just how old each
layer is
Fossils are within that time period
Most of these layers are sedimentary rock.
The Fossil Record of Horses
• Record shows size and shape progression
• Used to be as small as dogs!
Some fossils are simply older versions of insects much like those found on Earth today
The Fossil Record• A story we piece together as we find new
fossils– Clearly, the fossil record tells us of times when life
on Earth was very different than it is today– The story tells us life has gradually become more
complex.
a very scary salamander
Fossil of cells that resemble
modern cyanobacteria (3.5 billion years old)
Biogeography
The distribution of different organisms around the planet
Biogeography Video (7:03)
jack rabbit (a lagamorph) kangaroo (a marsupial) patagonian hare (a rodent)
These 3 organisms live in similar environments around the world (the US, Australia, and Argentina)
What is similar between these different animals?
Homologous Structures
Structures used for different purposes that indicate a common ancestry
Why would appendages used for different purposes have the same underlying bone structure?
Vestigial Structures
Structures that have no function in the organism
The only explanation is that they are remnants of evolution
Human Appendix
Whale HipsSnake SpursHuman Tail Bone
Comparative Embryology
Can you tell which is which? mouse, turtle, chick, pig, and human
Turtle Mouse Human Chick Pig
Why would all these very different organisms need to develop the same way?
Molecular Evidence
Compare DNA sequences of different organisms to see how similar they are!
% Similarity Between Species
Human DNA?
• 96% similar to chimpanzee • 85% mouse • 50% fruit flies
Just as DNA shows you descended from your parents it also shows you descended from the grandparent of them all ~3.8 billion yrs ago
Imperfections of Adaptations
The Panda’s Thumb– Eats bamboo, not meat– Developed thumb grasp bamboo– Not a perfect solution, but it works!
Important Points To Remember About The Process of Evolution
Evolution acts on populations not individuals
Individual organisms do not improve themselves
Nature selects the best of the members of a population to
survive and produce the next generation
Evolution does not produce new adaptations!
It amplifies (increases) or diminishes (decreases) variations that are already present
Mutations may produce such unique features but selection enhances them
