The Evolution of Microbial Life Chapter 15.

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1. Major Episodes in the History of Life. See figure 15.2
2. The Origin of Life

Comment: This material is highly speculative and we may never understand how the first cells arose. But these sorts of steps seem reasonable based on what we know today about chemistry. Also they Stage 3 and 4 may have happened in parallel. For instance small random polypeptides and RNA molecules show the ability to catalyze chemical reactions and some scientists have proposed that sets of these molecules, able to catalyze their own synthesis may have been an important first step. Some scientist even propose that the first replicating pre-cells may not have involved any sort of genetic material at all! The formation of pre cells involves the idea that certain common types of organic molecules such as phospholipids and proteins spontaneously self assemble into more complex structures. See figs 15.7. A good recent overview about self assembly is http://www2.bc.edu/~strother/GE_146/lectures/14.html
as well as this talk ( http://www.theharbinger.org/articles/rel_sci/fox.html ) given at the Vatican by one of the major investigators in this area, Sidney Fox. Self assembly is being exploited in the developing field of nanotechnology. See http://physicsweb.org/articles/news/8/6/7/1

But also see this highly skeptical paper: http://origins.swau.edu/papers/life/chadwick/default.html (I think the logic is flawed but worth looking at)

Here is a more balanced yet skeptical viewpoint: http://www.nytimes.com/library/national/science/040699sci-cell-rna.html

My own view point has not changed much since I wrote this essay in 1999: http://staff.jccc.net/pdecell/essays/notall.htm

3. Prokaryotes

The Bacterial Flagellum and "Intelligent Design":

The bacterial flagellum is often held up as a possible example of Intelligent design. Since it is composed of lots of different proteins including a rotating wheel it seems that it could not have evolved through a series of transition. The main advocate of this position is Michael Behe, for example on this intelligent design site. http://www.arn.org/docs/mm/flagellum_all.htm

But .....check out this site and rebuttal to Behe by Ian Musgrave:

http://www.health.adelaide.edu.au/Pharm/Musgrave/essays/flagella.htm

You read..you decide. :-)

Also here is a really cool site that discusses how the Bacterial Flagellum self assembles!

http://www.aip.org/png/2002/174.htm

A more general rebuttal to intelligent design arguements with special focus on Bacterial Flagella is http://www.millerandlevine.com/km/evol/design2/article.html


4. Protists

A good discussion of Dr. Margulis's work is http://www.nyu.edu/classes/neimark/margulis.html

Also check out this recent article: http://edition.cnn.com/2005/TECH/science/10/14/new.organism.reut/

Comment: Today some scientists suggest that the original function of mitochondria was not to produce ATP but to detoxify oxygen. Only later according to this hypothesis did the electron transport systems in the mitochondria become important for ATP production.  If true, then this would be an example of exaptation as defined in chapter 14.

5. Diversity of protists.

You might enjoy visiting my Protista pages at http://staff.jccc.net/pdecell/protista/protistframe.html

A much more comprehensive and interactive Protist site is at: http://www.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Protista/

Comment: The Kingdom Protista is structurally the most diverse of the currently recognized kingdoms. It is likely that this Kingdom will get broken up as we infer more about their evolutionary relationships. For instance the 'green algae' are quite different from each other and probably do not have an immediate common ancestor. Some of the multicellular algae are more like plants and probably belong in the plant kingdom. Chloroplasts in the protista are highly diverse and suggest several independent origins for photosynthesis in eukaryotes. Even the eukaryotes as a group may not have arisen from one type of prokaryote. For instance, the cell membrane of eukaryotes tends to be similar to that of bacteria but the DNA and ribosomes appear more similar to the Archaea, suggesting that the common ancestor of eukaryotes might have arisen from an ancestor that itself was an amalgam of bacteria and archaean cells! The biochemistry of prokaryotes and protists probably holds many suprizes for us!

6. Viruses: Genes in packages. Chapter 10 pp 188-189

 


pgd created 11/20/04 revised 04/08/06