Lecture 38 Preview

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

• Support from agreement between anatomical, fossil, and DNA studies

    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).

• From Geology:  The earth changes over time:  volcanoes, earthquakes, glaciers, tsunamis, movement of land masses, formation of mountains and valleys.

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

Organisms also alter the environment.

• Support from earth science studies:  the earth formed about 4.5 billion years ago; chemical elements in living things were present in the crust and atmosphere of the earth.

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.