Assignments for Friday's class:

Assignments for Monday's class:


Discuss Homework assignments

Hints on how I envisioned the answers are here, Jukes Cantor spreadsheets are here)

Discuss items that go beyond evolution by natural selection.

Natural Selection and Evolution

When does "evolution" occur? An algorithmic approach.

"Darwin's Dangerous Idea" by Daniel C. Dennett, Chapter on Evolution as algorithm is a reading assignment for Monday, Sept. 13. [available through WebCT]

What is needed for evolution to occur?

(Note, this is different from stating that this is all that occurs in evolution)

  • Offspring similar but not identical to parents
  • More offspring than necessary
  • Competition for resources, mates => survival of the fittest.

What processes in biological evolution may go beyond inheritance with variation and selection?

(Many of these conflict with the modern synthesis, NOT with the general definition of natural selection.)

  • Horizontal gene transfer and recombination
  • Polyploidization (botany, vertebrate evolution) see here
  • Fusion and cooperation of organisms (Kefir, lichen, also the eukaryotic cell)
  • Evolution of the holobiont (host + symbionts)
  • Targeted mutations (?), genetic memory (?) (see Foster's and Hall's reviews on directed/adaptive mutations; see here for a counterpoint)
  • Random genetic drift
  • Gratuitous complexity
  • Selfish genes (who/what is the subject of evolution?)
  • Parasitism, altruism, gene transfer agents
  • Mutationism, hopeful monsters

(links for Beatrix Potter and/or symbiosis fans: and and )

Go through coral of life ppt slides.


How old is life on Earth?

  • The Earth is about 4.5 Ga old, but no crustal rocks has survived from that time. The oldest rocks are no older than 4.0 Ga.

Morphological Fossil Evidence:
  • For about a decade the oldest microfossils were considered to be about 3.5 Ga old (see here). The fossils (as interpreted by Bill Schopf) look like "modern" Cyanobacteria. Compare the time to to molecular trees of life: Is this a problem? However, the evidence for these fossils was questioned.

  • 3.2Ga old filamentous fossils, probably of thermophilic chemotrophic prokaryotes (Rasmussen, 2000)

  • 1.8Ga old fossils from Gunflint formation: iron-loving bacteria and cyanobacteria
Biological Signature Evidence (examples):
  • Oldest geological evidence for life - 3.8 Ga ago - is based on 13C discrimination (carbon derived from living systems often have lower delta 13C values than inorganic carbonates) [here]. The rocks are from Akilia island off the coast of Greenland, and severely altered by metamorphism. However, recently the evidence for that was reassessed.

  • 2.7Ga old: probable biomarkers of cyanobacteria and of eukaryotes (Roger Summons, Roger Buick and Jochen Brocks)

See Olga's Timeline of the Universe here

If time slides on high temperature origin of life and the late heavy bombardment