are recognizable, physical evidence of organisms
that lived long ago–skeletons, shells, leaves, seeds, imprints of leaves
and tracks (trace fossils), and even fossilized feces (coprolites)
For fossilization, body parts or impressions must be buried in
rock before decomposition.
Over time, chemical changes and pressure transform living
structures into stony hardness.
Obviously, fossils form in highly unusual situations and therefore,
are very rare.
Interpreting the Geologic Tombs
, the layering of sedimentary deposits
bearing fossils, is quite similar from continent to continent.
Deepest rock strata are assumed to be the oldest, surface layers the
youngest. (big leap of logic…)
Abrupt changes in the fossils in the layers were the basis for
dividing earth history into great eras, which formed a "geologic time scale" to which actual dates
were added later.
Interpreting the Fossil Record
The fossil record is far from complete, but some lineages are
Fossil records vary according to type of organism (hard parts
preserve well, soft parts do not), stability of the geographical region
(sea floor vs. eroding hill), and quality of the specimen.
Evidence of a Changing Earth
According to the theory of uniformity,
mountain building and erosion had repeatedly changed the surface of the
Earth in exactly the same ways through time.
Alfred Wegener proposed a model of a single world continent, named
Pangea, that at one time extended from
pole to pole surrounded by a single huge ocean.
The idea of continental drift explains the separation of the
continents and the formation of great mountain ranges as the continents
collided (all through mantle convection)
Evidence From Comparative Embryology
Developmental Program of the Larkspurs
The common larkspur has a ring like array of petals to guide honeybees
to the nectar, plus bulging reproductive structures for the bee to hold on
A more recently evolved larkspur has tight flowers that discourage
bees but are attractive to hummingbirds.
Developmental Program of the Vertebrates
Different organisms may show similarities in morphology during their
embryonic stages that often indicate evolutionary relationships.
The early embryos of vertebrates strongly resemble one another
because they have inherited the same ancient plan for development (see Macroevolutionintro…)
Some of the variation seen in adult vertebrates is due to mutations
in genes that control the rates of growth of different body parts. (see
"From Fin to Hand")
One illustration of changes occurring in the timing of development is
the similarity in size of the skull bones of humans and chimps at birth,
which becomes dramatically different as these two animals age. (see "Retardation
Evidence of Morphological Divergence
In morphological divergence, features have departed in appearance
and/or function from the ancestral form.
These are body features that resemble one another in form or
patterning due to descent through common ancestors.
Analogous body parts perform similar functions in dissimilar and
distantly related species.
is the adoption of similar
function over periods of time in animals of evolutionary remote lineages.
A good example of analogy is the similarity of function but not
structure of the wings of an insect, bat, and a bird.
Evidence from Comparative Biochemistry
mutations have no more measurable effect on
survival and reproduction rates than do other alleles for the trait.
These mutations accumulate in the DNA and can be used as a "molecular clock" for (back) dating times of
divergence of species.
This model has three important assumptions.
The "Lucy" theory.
Because genes dictate the sequence of amino acids in proteins,
analysis of proteins can determine the similarity of genes between
For example: The amino acid sequence of cytochrome c shows strong evidence for placing
humans, chimps, and rhesus monkeys in the same group.
See Dr. Doolittle's Hemoglobin analysis.
Nucleic Acid Comparisons
The degree of similarity of nucleotide sequences of DNA reveals
information about evolutionary relationships.
If a single strand of DNA from one species is allowed to recombine
with a single strand of DNA from another species (DNA-DNA hybridization),
the degree to which they match up is a measure of similarity.