The Macroevolutionary Puzzle

                              1.Evolution proceeds by modifications of organisms that
                                already exist.

                              2."New" species emerge as mutation, natural selection, and
                                genetic drift change allele frequencies in reproductively
                                isolated populations.

                    I. Fossils–Evidence of Ancient Life

                        A.Fossilization

                              1.Fossils 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)
                                   a.For fossilization, body parts or impressions must be
                                     buried in rock before decomposition.
                                   b.Over time, chemical changes and pressure
                                     transform living structures into stony hardness.

                              2.Preservation is favored when organisms are buried rapidly
                                in the absence of oxygen and the burial site is left
                                undisturbed.

                        B.Interpreting the Geologic Tombs

                              1.Stratification, the layering of sedimentary deposits bearing
                                fossils, is quite similar from continent to continent.

                              2.Deepest rock strata are assumed to be the oldest, surface
                                layers the youngest.

                              3.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.

                        C.Interpreting the Fossil Record

                              1.The fossil record is far from complete, but some lineages
                                are extensive.

                              2.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.

                    II. Evidence From Comparative Embryology

                        A.Developmental Program of the Vertebrates

                              1.Different organisms may show similarities in morphology
                                during their embryonic stages that often indicate
                                evolutionary relationships.
                                   a.The early embryos of vertebrates strongly resemble
                                     one another because they have inherited the same
                                     ancient plan for development.
                                   b.Some of the variation seen in adult vertebrates is
                                     due to mutations in genes that control the rates of
                                     growth of different body parts.

                              2.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.

                   III. Evidence of Morphological Divergence

                        A.Homologous Structures

                              1.In morphological divergence, features have departed in
                                appearance and/or function from the ancestral form.

                              2.These are body features that resemble one another in
                                form or patterning due to descent through common
                                ancestors.

                              3.A good example of homology is the similarity of the
                                structure of the bones in forelimbs of birds and bats.

                        B.Potential Confusion from Analogous Structures

                              1.Analogous body parts perform similar functions in
                                dissimilar and distantly related species.

                              2.Morphological convergence is the adoption of similar
                                function over periods of time in animals of evolutionary
                                remote lineages.

                              3.A good example of analogy is the similarity of function but
                                not structure of the forelimbs of sharks, penguins, and
                                porpoises.

                   IV. Evidence from Comparative Biochemistry

                        A.Molecular Clocks

                              1.Neutral mutations have no more measurable effect on
                                survival and reproduction rates than do other alleles for
                                the trait.

                              2.These mutations accumulate in the DNA and can be used
                                as a "molecular clock" for (back)dating times of
                                divergence of species.

                        B.Protein Comparisons

                              1.Because genes dictate the sequence of amino acids in
                                proteins, analysis of proteins can determine the similarity
                                of genes between species.

                              2.For example: The amino acid sequence of cytochrome c
                                shows strong evidence for placing humans, chimps, and
                                rhesus monkeys in the same group.

                        C.Nucleic Acid Comparisons

                              1.The degree of similarity of nucleotide sequences of DNA
                                reveals information about evolutionary relationships.

                              2.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.

V. Identifying Species, Past and Present

                             1.The binominal system was originated by Carl von Linné,
                                better known as Linnaeus.
                                   a.The first part of the scientific name was the genus
                                     (always capitalized and italicized) and signified very
                                     closely related organisms.
                                   b.The second part was the specific name (never
                                     capitalized but always italicized) and signified an
                                     even closer, interbreeding relationship.
 
                        B. Groupings of Species—The Higher Taxa

                              1. The main taxa of the hierarchy from most to least inclusive
                                are: kingdom >>> phylum >>> class >>> order >>>
                                family >>> genus >>> species.
 
                   VI.Finding Evolutionary Relationships Among Species

                        A.The Systematics Approach

                              1.Evolutionary systematics is the branch of biology that
                                applies evolutionary theory to the task of identifying
                                patterns of diversity over time and in the environment.