Transcript Descent With Modification

Descent With
Modification: A
Darwinian View
of Life
Campbell Chapter 22
What Evolution Is
•Descent with
modification
•Change in
genetic
frequencies
over time
Change with
inheritance
•
From http://evolution.berkeley.edu/evosite/evo101/IIntro.shtml
What Evolution
Isn’t
•It is not a
theory that
says
humans
came from
apes!
Historical
Context of
Evolution
People have always
wondered about the
origin of diverse life
forms on Earth.
Aristotle and Scala
Naturae
•Aristotle believed
that there was a
Divine Creator at
the top of a ladder,
and everything
else descended
from that being.
From http://www.ivirgil.it/set/Darwin/creazionismo.htm
Carolus Linnaeus
•Created a
system of
taxonomy that
did not show
relationships
between
organisms.
Georges Cuvier
•Observed
•
changes in fossil
layers of rock
Surmised that
layers were
different due to
catastrophes
(floods, ice ages)
Lamarckian
View of
Evolution
What Lamarck
Observed
•More modern fossils
were found in upper
layers of rock
This led to the formation
of more modern species
•
Use and Disuse
•Body parts used
to get along in the
environment get
stronger and
larger
Those that aren’t
used, deteriorate.
•
Inheritance of Acquired
Characteristics
•Modifications
acquired during
an organism’s
lifetime could be
passed on to
their offspring.
Dispelling the
myths
•Neither of these
things were
possible
because they
were missing a
very important
component…
Darwinian View
of Evolution
Darwin backgrounder
• Grew up very
•
•
wealthy, educated
Was a med
student, then a
divinity student
Served as a
naturalist for British
government on the
HMS Beagle
Where Darwin Went
Development of Theory of
Natural Selection
• Darwin observed 12 species of finches
• Noted differences in beaks and how that
correlated to food choice
What Darwin noticed
•Organisms on the
•
South American
continent looked like
those on the
Galapagos but didn’t
live anywhere else
Was influenced by
Lyell (Principia Geologica)
Descent with Modification
•Supposed that all organisms were
related to an ancient ancestor
Natural
Selection
After studying specimens he
collected, analyzing data and reading
an essay by Thomas Malthus, Darwin
formulated a theory that explained
how different species originated.
Tenet #1
•Variation exists among members of
a species.
Tenet #2
•This variation is inherited.
Tenet #3
• There are limited resources in the
environment. There is a struggle for
survival.
Tenet #4
•Organisms with favorable traits
are more fit, thus they leave
behind more offspring than those
who are less fit.
Tenet #5
• These favorable traits persist in the
population and will become more frequent.
Result:
•Differential reproductive success
leads to change in favorable
traits among generations
In sum…
•Natural selection occurs as a
result of interactions between the
environment and the genetic
variability demonstrated in living
organisms.
It is the result of differential
reproductive success.
•
Artificial Selection
• Organisms with certain traits are bred
•
repeatedly until population has only that trait
Dog breeds are another good example
Other Evidence for
Evolution
• There is other
evidence that
evolution has
occurred:
 Anatomical
 Molecular
 Fossil
Record
 Biogeography
Fossil of Archaeopteryx, ancient bird
Homologous Structures
Vestigial Structures
• Structures which are
•
•
•
smaller or reduced in
size because they are
no longer used/needed
Whale pelvis
Vestigial legs on
snakes
Human appendix
Embryological Similarities
•Presence of
•
post-anal tail,
pharyngeal gill
slits indicates
common
ancestry
What else does
it indicate?
Molecular homologies
•Amino acid sequences among
•
vertebrates have similarities
What else is similar?
Fossil Record
•Transitional
forms show
the change
from simpler
forms to
more
complex
forms
Biogeography
•Geographic distribution of species
•Similar species live in the same
area