It Rained Last Night
What evidence can you come up with to
support this statement?
*The streets and sidewalks have puddles of water
*The cars are still wet or streaked.
*Someone had an event last night that was cancelled because of the
rain.
*Your shoes you left outside are soaked.
*There is a certain smell in the air (creosote in AZ)
*It is humid and cloudy
It’s a theory…..
An accepted scientific theory is a
statement based on observation
and experiment.
It is repeatedly tested and
confirmed through experiment and
observation.
It is a widely accepted statement
based on scientific evidence that
helps explain a group of facts.
Theory of Evolution
Germ Theory
The Theory of Gravity
The Theory of Evolution makes two bold claims
-All living things on Earth are related. Have evolved from a common
ancestor.
-The evolution of living things is powered by natural process that can be
observed and understood.
Extraordinary claims require evidence
What is the evidence for evolution?
Independent Lines of Evidence
*Comparative Anatomy
*Embryology and Development
*Fossil Records
*DNA Comparison
Cetaceans (or whales) evolved
from a four legged, land
walking ancestor.
Comparative Anatomy
Whales are mammals…
*Have placenta and give
live births
*Feed milk to their young
*Are warm blooded
*Do not have gills but
breathe with lungs
*Have hair
*Have blow holes, but
are nasal passages
when looking at the skull.
Evolved from four
legged, land walking
mammals….
Comparative anatomy
Homologous Structure:
Whales have arm, wrist, hand and finger
bones…similar to cats, bats, hippos and
people.
is an organ or bone that
appears in different
animals, showing
commonalities
demonstrating descent
from a common ancestor.
*In other words, it's when
very different animals have
bones that appear very
similar in form or function
and seem to be related.
Same structure, but different
function.
Homologous
Structures
(Same)
Back legs!? Not actually
functional legs, but there are bones
there that don’t serve a purpose.
*Hip bone (Ball and socket joint)
Thigh and shin bone.
WHY?
Vestigial Organs:
Physical structures that
were fully developed and
functional in an ancestral
group but are reduced and
unused in the later species.
These bones do not serve a function or purpose
but they do provide some evidence of the claim.
Embryology and Development
Compare Embryos of different species
at different stages of development.
Spotted Dolphin 5
weeks
These two lines of evidence tell the same story. lets look at another line of
evidence to confirm that ancestors of whales where four legged land walkers.
What does the fossil record show? We
should be able to see stages of
development. Or intermediate fossils.
Basilosaurus 30-40 MYA
Fully formed back legs (hip, thigh,
ankle, toes) Was small and not very
strong. Likely was not very useful.
Maiacetus 50 MYA
*Legs sturdy
enough to walk
on.
*Found among
marine fossils
*Same teeth and
ear bone structure
as basilosaurus
and modern
whale.
Artist
depiction
Modern Dolphin:
Nasal passage on top.
Basilosaurus:
Nasal passage in the
middle.
Maiacetus:
Nasal passage at the end
DNA Comparison
-Compare DNA code of different organisms to find out who is most
closely related to who.
-When Whale DNA is compared to other animals we find that the closest
genetic match is to the hippopotamus.
*Does NOT mean that they evolved from hippos, but that they both evolved
from some common ancestor
Hippos and Whales:
-Maiacetus have specially shaped ankle bones
found only in hippos.
-Hippos give birth and nurse underwater
-Both have multi chambered stomachs
-Both missing coat of fur
Homologous Structure:
Very different animals have bones that appear
to be the same in form and function. Are the
same in structure, but may not perform the
same function.
Analogous Structure:
Body part in different species that is
similar in function but not in
structure that evolved in response
to a similar environmental
challenge.
Same structure, but does not function
the same (walking, swimming)
Different structure, but same function (Flying)