Evidence of Evolution
Models of Evolution
Gradualism, Punctuated Equilibrium
& Endosymbiont Theory
TEKS
• 7B analyze and evaluate scientific
explanations concerning any data of sudden
appearance, stasis, and sequential nature of
groups in the fossil record.
• 7G analyze and evaluate scientific
explanations concerning the complexity of
the cell.
“In”
• Does evolution occur in rapid bursts or
gradually (over time)?
• This question is difficult to answer because we can't
replay the past with a stopwatch in hand.
• However, we can try to figure out what patterns we'd
expect to observe in the fossil record if evolution did
happen in bursts, or if evolution happened gradually.
• Then we can check these predictions against what
we observe.
Lets take “A Peek at the Past”
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Let’s read the intro to this activity together
Follow directions as stated
Class discussion
Answer discussion questions
Lab Directions
• Place the organisms in their proper layer.
• If the organism does not say upper or lower
just place them in the box.
• If you have more than two organisms in a
layer, you must look at similarities and
differences between the organisms
– If the organism is slightly different…place it slightly
to the right of the organism below it
– If the organisms is completely different ….place it
to the extreme right
Models of Evolution
Which diagram shows gradualism and
which shows punctuated equilibrium?
Graduated.
Why?
Punctuated Equilibrium.
Why?
What should we observe in the fossil
record if evolution is slow and steady?
• If evolution is slow and steady, we'd expect to
see the entire transition, from ancestor to
descendent, displayed as transitional forms
over a long period of time in the fossil record.
In the example, the
preservation of many
transitional forms, through
layers representing a length of
time, gives a complete record
of slow and steady evolution.
Transitional forms in the fossil record
• In the example are just a few steps in the
evolution of whales from land-dwelling
mammals, highlighting the transition of the
walking forelimb to the flipper
• Shows a slow & gradual change
• Gradualism
What would we observe in the fossil record
if evolution happens in "quick" jumps
(perhaps fewer than 100,000 years for significant change)?
• If evolution happens in "quick" jumps, we'd expect to
see big changes happen quickly in the fossil record,
with little transition between ancestor and
descendent.
• Punctuated Equilibrium
What happened
to all the ones in
the middle???
Does a jump in the fossil record necessarily
mean that evolution has happened in a
"quick" jump?
• Sometimes a jump in the fossil record can also
be explained by irregular fossil preservation.
• Some fossils were not preserved….the missing
link!
Stasis
• Stasis: a period of little or no evolutionary
change in a species in the punctuated
equilibrium model
Stasis
• Stasis: A population of mollusks is
experiencing stasis, living, dying, and getting
fossilized every few hundred thousand years.
Little observable evolution seems to be
occurring judging from these fossils.
Identify which is gradualism or
punctuated equilibrium
Punctuated
Gradualism
Endosymbiont Theory
• By reading the article you will be able to
answer how….
– bacteria evolved to plants and animals today?
– a prokaryote evolved to a eukaryote?
Ticket-Out-the-Door
• Answer questions