Download Evolution - El Camino College

Macroevolution
Website: http://evolution.berkeley.edu/
Descent with modification as a theory
One of the strengths of a theory
is that it can be tested
using independent lines of evidence
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Fossil record provides snapshots of the past
 remains of organisms or signs of organisms preserved over time
 Shows different life forms and also clues to the way they lived
Fossil record supports descent with modification
If one species descended from another:
Fossils should show an ordered pattern
(through time one form is replaced by
similar but different forms)
EVIDENCE
 Fossil record shows that
organisms have appeared in
an ordered and consistent sequence
 Fossils that show the intermediate states
between an ancestral form and that of its
descendants,
are called transitional forms
example: Tiktaalik
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Do gaps on the fossil record disprove evolution?
Fossils link
ancestral species to those living today
and
also link two species living today
Today’s species do not look very similar,
but as we go lower in the fossil layers
the differences disappear
3
Geographical distribution of organisms on the earth
supports descent with modification
If one species descended from another:
there should be some geographic continuity from where the ancestor
species and the descendent species are found
Look who lives in America and is a marsupial?
Marsupial mammals are found in the Americas as well as Australia
They are not found swimming
across the Pacific Ocean,
nor have they been discovered
wandering the Asia.
How could marsupials have gotten
from one place to a location half a world away?
4
Continental drift
Continents have been and are constantly on
the move
Caused by
Constant slow movement of plates of earth’s
crust on the underlying molten mantel
Continental drift animation
Continental drift shows that continents
came together 250 mya and drifted apart 180 mya
Marsupials rode the continents to their present positions
5
DNA and protein sequences
support descent with modification
If one species descended from another
we expect that similar species should have similar DNA or similar proteins
6
Structures present during embryo stages
support descent with modification
Since embryo development is coded in the DNA
(inherited and changeable)
Related species will have similar embryo development
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