Theory of Evolution
part II

Evidence for Evolution
Inferences about the
history of life are based on
the assumptions of certain
geological principles.

Nicolaus Steno (1638-1687)
Steno's Law of Superposition

James Hutton (1726-1797)
Uniformitarianism: “ The present is the key to the
past”
the fundamental principle that
geological processes and
natural laws now operating to
modify the Earth's crust have
acted in much the same
manner and with essentially the
same intensity throughout
geologic time, and that past
geologic events can be
explained
by forces observable today;

Charles Lyell (1797-1875)
first geologic time scale
proposed an older earth
than was previously
accepted
Lyell’s text influenced
Darwin’s ideas

Relative Age generally relies on position
within the geologic column in reference
to index fossils.
Absolute Age generally relies on the
rate of decay of various radioactive
isotopes.

The amount of time it takes for 1/2 of a
radioactive isotope to decay to non-
radioactive form is known as half-life.

Generalized presentation of Geologic
time and the appearance of life forms.

The Fossil Record
paleontologist- scientist who study fossils
Fossils are the preserved remains or
traces of once living organisms
the cumulative collection of fossils
represents the “Fossil Record”

The Fossil Record
While there are gaps, paleontologists can offer
a relatively clear picture of the evolution of
many organisms.
tells us of major changes in climate and
geography
as environments changed over earth’s history,
changes in living things followed

How fossils form
frozen in ice
trapped in hardened tree sap
peat bogs, quicksand, tar pits
most are found in sedimentary rock

Problems in Assembling
the Fossil Information
all of the fossil “puzzle pieces” are not in
place
many organisms may live and die
without leaving a trace
fossil bearing rocks must be exposed to
weathering

Evidence from Living
Organisms
homologous
structures- similar
structures adapted
to different
environments

Evidence from Living
Organisms
vestigial organs- organs or structure that
seem to serve no useful purpose

Evidence from Living
Organisms
Structural homologies support common
descent with modifications
If organisms had arisen independently,
there would be very little chance of
these similarities
Each new species adapted what was
present in the species before it.

Evidence from Living
Organisms
similarities in embryo development with
the passage of time, embryos become
more dissimilar
Biochemical similarities- DNA, ATP

Evidence from Living
Organisms
Modern Synthesis
Integrates the new genetics with
natural selection.
Ancestral relationships (phylogeny)
modeled as a branching tree.
Cladistics - branching tree cladagram
from comparing shared characters to
derived characters

Protist Fungi Plants
Archeabacteria
Animals
Eubacteria
Common Ancestor