Lecture 28 Preview

Support for the Theory of Evolution by Natural Selection Came from Many Areas of Science   

What acts as a selective barrier between the inside and the outside of all cells?


What molecule carries information passed from one generation to the next in all cells?


What molecule carries energy released from glucose and then releases energy for movement and synthesis in all cells?


What are the two processes by which all cells use information in nucleic acids to make proteins?



Fossils = mineralized remains or impressions (e.g. tracks) of organisms, usually in layers of rock (sedimentary rock)

   Record incomplete

    only some conditions right for preservation

    only some parts preserved

    only some found millions of years later


  Dating of fossils

    absolute age by chemical composition (radioactive isotopes)

    relative age by depth of rock layers



    different species appear at different times in the fossil record

    some species go extinct



Based on "descent with modification" what should appear first:  complex or simple forms? 

                                                 First appearance in fossil record (millions of years ago)

Prokaryotic cells                                                                        3500

Protists                                                                                      1500-1800

Multicelled eukaryotes                                                                1000

Vertebrates                                                                                  550



    If Evolution by Natural Selection occurs, different species should have some shared features from their common ancestor (shared derived characteristics).  Also, since differences take time to accumulate, two groups sharing a most recent common ancestor farther back in time can accumulate more differences than two groups sharing a most recent common ancestor closer to the present.  Or put another way, two groups with a most recent common ancestor closer to the present would share more derived characteristics.

   Cladograms are branching diagrams to represent evolutionary relationships among organisms, based on shared, derived characteristics.  They provide insight on

                     which organisms share a most recent common ancestor closer to the present time

                     which shared derived characteristics originated earlier and later

                     which characteristics were important in the splitting off of groups

    Organisms can be placed in cladograms, showing key shared derived characteristics allowing a new group to branch off; the relative time of branching agrees with  relative time of appearance of the new group in the fossil record.  More similarities are observed between organisms that have a common ancestor closer to the present (that branched off from each other more recently).


Which of these organisms share an ancestor closest to the present time?


Which characteristic (character) should appear earliest in the fossil record?


DNA of organisms with most recent common ancestors closer to the present (based on fossils) is more similar.  DNA of organisms with most recent common ancestor farther back in time is more different (has accumulated more differences).


How might continental drift (plate tectonics) lead to formation of new species?


Organisms also alter the environment.






Life forms have appeared over the last 3.5 billion years

Humans have been on earth only a small fraction of the earth's lifetime.

In the history of life there have been

    mass extinctions

    evolutionary  radiations


Humans have an increasingly large influence on the fate of other species.