Wednesday, August 4, 2010

Meeting Summary Aug. 4 2010

OK, here's what I have scribbled down by way of "minutes". BTW, I'm going to farm this job out next week, so one of you should step up or I will assign it (to someone other than Mitchell, who already got kudos for setting the blog up).

Big Question: Would plants be here without us? Maybe, in the sense that if we were suddenly erased, they might stay alive. However, if we (i.e. animals) were never here, would plants have evolved? There are reasons to think not. Good question.

We discussed several appearances of "detail" in biology - particularly with regard to hereditary disorders. Sickle-cell anemia is an example of a genetic distribution that does not conform to Hardy-Weinberg distribution (resting distribution for Mendelian single-allele heredity in absence of selection). Reason is that heterozygotes are malaria-resistant. Other examples of bad genes also appear, and in many cases can be traced back to "bottleneck" effects - the legacy of past times when the population became very small. Megan put forward a name: "Six Eves Hypothesis", and mentioned that sub-saharan africans have more diversity than non-africans and that humans have less diversity than other animals. This indicates bottlenecks were important.

Incidentally, This is also probably why Tay-Sachs disease is more common in european jews, which have definitely been through population bottlenecks and whose rate of gene transfer with outside populations is restricted by the details of how judaism is passed down (through the mother). This is likely acute in the orthodox population, where conversion may not be recognized at all.

The above issues were connected to the Biologist/Physicist dichotomy, because these are all cases where past details matter. (Incidentally a good word to associate with this sort of phenomenon is "non-markovian". I'll explain that later.)

Another example of where "physicist-like" thinking goes wrong is Levinthal's paradox. Protein sequences are not chosen from a random heteropolymer-like distribution, but have been selected for foldability.

Reindeer feet don't freeze; neither do arctic fish. The reason is lipid composition, which is interesting because lipids aren't hereditary material.

Equilibrium is the state which is maximally non-commital with respect to information not contained in a set of constraints. It is TRANSITIVE. This implies that to know everything about one part of a system at equilibrium, you have to know everything about the entire system. The only way that a part of the universe can be at zero degrees is if the whole universe is at zero degrees. The statement of equilibrium spreads out what you don't know over everything in the equilibrium.

We agreed to meet Friday at 11-1. We can't do this, because the room isn't free until noon. I propose that we do it at noon, and only meet for an hour.

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