Homework
• Directed
Reading
Chapter 5 Section 1
#1-17
Create a Species Project
Learning Targets
•I
can explain how comparing
organisms can provide evidence
that they have common
ancestors.
What is the evidence for
evolution?
1.
Fossil Evidence
2.
Homologous Structures
3.
Vestigial Structures
4.
Comparative Embryology
5.
Genetic (DNA) Comparisons
Which piece of evidence do you
think is the most important for
evolution?
I. THE FOSSIL RECORD
I. THE FOSSIL RECORD
Importance
• Provides
the best proof of the
history of life showing how
extinct species have led to
today’s species
“Lucy”, 3.2 MY
Archaeopteryx, 150 MY
Becoming a Fossil (Part 1)
(excerpts from Bill Bryson’s book)
In order to become a fossil, several things must happen. First, you must die in
the right place. Only about 15% of rocks can preserve fossils, most being
sedimentary rocks. So the deceased usually needs to become buried in
sediment, the best chance is being buried underwater and decomposing
without exposure to oxygen, allowing the bones and hard parts, and
sometimes soft tissue, to be replaced by dissolved minerals, creating a
petrified stone version of itself. Then as the sediments in which the fossil lies
are pressed, folded and pushed about by Earth’s processes, the fossil must
somehow maintain an identifiable shape. Finally, after tens of millions to
hundreds of millions of years of being hidden away, it must be found and
recognized as something worth keeping.
•
Why do you think the fossil record (almost 95% of it) is mostly marine life?
Formation of Fossils (Summary)
•
Organism is buried in sediment under water (sometimes: ice, amber or tar)
•
Hard parts (bone& shell) are slowly replaced by minerals dissolved in water
Transitional Species (Common Ancestors)
•
Location where two species
evolutionary path connect on the
“tree of life”
•
Scientists search for common
ancestors in the fossil record to
show the evolutionary connection
between species & how they
change over time.
The Mammalian Family Tree
A dead end branch
represents an extinction.
Where is the most
recent common
ancestor between
squirrels and whales?
All these species can
trace their lineage back
to this common
ancestor, essentially the
first mammal.
Cladogram
Transitional Species Example – Whale Evolution
* Read more on Whale Evolution in the textbook (pgs 112-113)
* Whale Evolution video clips
Becoming a Fossil (Part 2)
(excerpt from Bill Bryson’s book)
It isn’t easy to become part of the fossil record. The fate of
nearly all living things (over 99.9% of them) is to decompose to
nothing. Even if you make it into the small pool of organisms,
that don’t breakdown to nothing, the chances of being
fossilized are very small. Only about one bone in a billion, it is
thought, ever becomes fossilized. If that is so, it means that the
complete fossil legacy of all the Americans alive today (that’s
about 300 million people with 206 bones each) will only be
about 50 bones, one quarter of a complete skeleton. That’s
not to say that any of these bones will actually be found. Fossils
are in every sense extremely rare. Most of what has lived on
Earth has left behind no record at all. It has been estimated
that less than 1 species in 10,000 has made it into the fossil
record. What we have in the fossil record is the smallest of
samplings of all the life that has existed on Earth.
Completeness of the Fossil
Record?
How do we know how old a fossil is?
TWO Ways to Date Fossils
Relative Age Dating
•
Approximation of dating
by comparing rock
layers
Absolute Age Dating
•
Precision of dating by
measuring radioactive
decay of elements in
rock
Relative Age Dating
•
Relative age dating follows the Law of Superposition
(older rocks are found under younger rocks)
•
Exception to the rule – unconformities (break in the rock
record)
•
Index Fossil – an organism that lived during a specific
period of time and is abundant.
Absolute Age Dating
•
Radioactive Elements: unstable atoms give off radiation
(protons & neutrons) to become stable.
•
•
Ex: Uranium-238 & Carbon-14
Radioactive dating: Radioactive decay (going from unstable
to stable) occurs at a constant rate called a half life. Each
radioactive element has its own half life.
•
Half life: the amount of time it takes for half the radioactive atoms
in a substance to become stable.
• Examples:
Uranium-238 has a half-life of 4.5 billion yrs (becomes Lead)
• Carbon-14 has a half-life of 5730 yrs (becomes Nitrogen)
•
Example of Absolute Age Dating
Red Dots are radioactive elements
Green Dots are stable elements
Uranium-235 has a half-life of 700 million years. How much of the 12 g
sample of Uranium-235 will be left after :
a. 700 million years _______
b. 1400 million years _______
II. Comparative Anatomy
• Homologous
• Vestigial
Structures
Structures
Homologous Structures
• Body
parts from different organisms
that have the same structures, but
different functions, supporting the
idea of a shared common ancestor
• EX:
vertebrate
forelimb
bones
Homologous OR Not?
Cephlopod
Cnidarian
Arthopod
Mammals
Homologous OR Not
Homologous Structures between species
provide evidence that the species shared a
common ancestor, as shown in the mammal
forelimb examples
•
All display the same structure but adapting
different functions for their forelimbs.
Some times in nature, unrelated species will
evolve similar functions through different
evolutionary paths using unrelated structures.
•
These types of structures are called
Analogous Structures and they do not show
evidence of evolution from a common
ancestor.
Bird wings
Bird wing
Bat wing
***Bird and bat wings
have separate
evolutionary origins BUT
are superficially similar
because they evolved to
serve the same function!!!
Common Ancestors
Homologous structures are inherited
from common ancestors.
• The octopus limb could only be
homologous to the lizard limb if they
both inherited the limb from a common
ancestor.
• This family tree shows how the
octopus is related to vertebrate limbs.
Vertebrate limbs and octopus
limbs evolved independently
after their point of common
ancestry
• Not inherited from a common
ancestor
• Not homologous, they are
considered analogous.
• The same is true of the
grasshopper leg.
Vestigial Structures
• Structures
that are found in an organism but
appear to serve no function (reduced in size)
• they are remnants or “left overs” of an
organism’s evolutionary past
Ex: Whales and snakes have pelvic bones;
manatees “sea cows” have finger nails on their fins
• Humans?
•
•
•
•
•
•
•
ear muscles
canine teeth
Goose bumps
appendix
Tail bone
Wisdom teeth
Tailbone
Wisdom teeth.
Remnant of
earlier primate
ancestors with
tails
Leftover from
our ancestors
with larger
jaws
This is why wisdom teeth are so commonly
removed. Modern humans’ jaws tend to be too
small, so the teeth get impacted. Some people
never even develop wisdom teeth.
The same muscles
(arectores pilorum) that
enable a cat to do this:
also enable us to do this:
Hiccups, which
occur in many
other animals, are a
result of a nerve
misfiring and telling
your epiglottis to
close off your
trachea.
Its purpose can be
traced back to the
first organisms with
lungs (which
incidentally still had
functioning gills as
well).
This function can still be
seen in modern tadpoles.
It’s what keeps their lungs
from filling up with water
while they’re still using
their gills.
III. Comparative Embryology
• Similarities
in the developmental pattern of
organisms exist because of a common
ancestor
vestigial gill slits/pouches
• bony tail
• covered in a fine hair
• Two chambered hearts
•
Human embryo
Pig embryo
Chicken embryo
Can you guess what type of animal this
is?
Can you guess what type of animal this
is?
Turtle embryo
See the
developing
shell?
Comparative Embryology in Vertebrates
•All vertebrates
(related species) are
similar in early
stages of
development.
•Differences
accumulate as
development
continues.
•New development
instructions are
added to old
instructions
inherited from
common ancestors.
Comparative Embryology in Vertebrates
Human
embryo 5
weeks after
conception
1
cm
What animal is this?
Notice the
leg buds
Spotted dolphin
Both embryos at about 5 weeks gestation!
IV. Comparing Genetics
• An
organism’s evolutionary history is held
in their DNA sequence (genetic code)
• If a species changes, their DNA changes
• Genetic testing compares the similarity of
DNA between organisms
• The more closely related the species are
to each other the more similarities they
share in their DNA
Tomorrow we will explore
how well you understand
the evidence for evolution
EGG HUNT
What is the evidence for
evolution?
1.
Fossil Evidence
2.
Homologous Structures
3.
Vestigial Structures
4.
Comparative Embryology
5.
Genetic (DNA) Comparisons
Exit Ticket - Which piece of
evidence do you think is the most
important for evolution? Why?