Comment by siglesias | Hacker News Reader

Comment by siglesias | Hacker News Reader

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Let the Kuhn v. Popper debates begin...

EDIT: To clarify, using the term "erroneous" under the Kuhnian view (disclaimer, my view), is a bit disingenuous because the criteria under which we are claiming these theories to be wrong did not exist in their historical contexts: on the contrary, some of these theories, such as gravity, happenned to be progressive, brilliant, and in some cases extremely useful as a simplifying framework in the next paradigm. All of the historical and technological ingredients, such as the ability to calculate the speed of light accurately, or Maxwell's equations didn't exist for Newton. Do we call that he missed it an error?

In my opinion, "erroneous" as a term should be reserved for beliefs that were incorrect given existing frameworks: Lamarkian evolution, Einstein's cosmological constant, the postulating of the lumeferious ether, Hilbert's axiomatic program that was disproven in his time by Godel...THESE were erroneous.

It would be like saying in the future when (hypothetically) a more advanced technology comes along and computes a totally revolutionary and paradigm-shifting scientific framework that our views in 2010 are "erroneous". Probably a little extreme.

>the postulating of the lumeferious ether

Fairly sure that's the just a progressive step towards Einstein's model.

It is difficult to define wrong in a scientific context since everything is just model that matches observations. Of course, as more observations come, models will be naturally disproved. That doesn't mean they were wrong for the entirety of their existence which I think was your point, but you haven't applied it to the examples you raised.

In the example of ether, It was believed to be permeate all matter and the medium for light to travel through. It explained all observations at that time until the Michelson-Morley experiment which settled it.

I agree that wrong is difficult to define in these contexts, but remember that the only proof of the existence of the ether was that 1) light was thought to be a wave by the mathematical formulation of Maxwell, and 2) all known waves had a physical medium. That's it. It was a very ad hoc construction that immediately presented ways to test it. When it was tested by the MM experiment, it turned out to be undetectable at best, thereby exposing its weakness as a theory. Einstein didn't use the theory as a springboard because it was so good and useful; he used it as a springboard because it was so bad.

Aside: it's looking like Lamarck was right.

I'd really like some detail on this...

Basically, some life events lead to inheritable changes. The mechanism is apparently methylation (or other similar changes) to the DNA. Why this is inheritable I do not understand.

One rather relevant example from a recent new scientist that, in rats, overweight dad rats had offspring who more likely to get diabetes.

I get the impression it's early days with all this stuff, but it's going to be interesting.

http://en.wikipedia.org/wiki/Epigenetics

http://www.sciencedaily.com/releases/2005/10/051026090636.ht...

http://ndt.oxfordjournals.org/content/24/4/1088.full

Most of our epigenetic information is reset when we reproduce. Epigenetic changes play a big role in the differentiation of cells into their different types; since epigenetics changes the expression of genes, it can make cells behave differently. There are several methyltranserase enzymes whose job is to set up methylation patterns in the different types of cells while the embryo is still developing.

Methylation of DNA tends to persist through cell division because there are enzymes which approximately copy over the methylation patterns during DNA replication. If some epigenetic changes happen in sperm or eggs, then some of this may be carried over to offspring. You're right that we're still in the early days of mapping this out and understanding it. Molecular biology is a crazy mess that makes the worst spaghetti code look downright reasonable. That's evolution for you....

DNA methylation is heritable because the DNA strands that are methylated become part of the gametes and thus part of the developing fetus. The DNA is physically modified, and that same modified DNA combines with DNA from the other parent to form the DNA for the child.

This is an oversimplification, but imagine you have a sweater that you dye bright green. You then unravel it and use part of the yarn, along with yarn from another sweater, to knit a new sweater. Some of the new sweater will have the same physical change, the bright green dye, that the old sweater had.

> that same modified DNA combines with DNA from the other parent to form the DNA for the child.

Sure, but only cell#1 has the actual molecules from the parents.

Cell division requires that the DNA be replicated. What surprises me is that the replication step (apparently) preserves methylation. (If it didn't, there would be no observable epigenetic effect in the organism).

i.e. from an information perspective, the bits encoded in the DNA aren't don't just come from the sequence of bases, but also "out of band" data.

Strongly suggest that you read What is Life by Lynn Margulis and Dorion Sagan.

In it the authors discuss the evolution of the eukaryotic cell: a multi-part cell that evolved due to penetration or symbiosis of multiple organisms. Pretty much all complex life evolved out of eukaryotic cells. In particular the mitochondria that power your cells did not evolve from the same stuff that the rest of your cells did -- they were an addition later on.

Likewise, most of the genetic diff between us and Chimpanzees (or for that matter, blue green algae) are from external sources -- viruses and 'parasites'.

For that matter, 90% of the cells in your body are not genetically yours -- they are other microbes (though these account for only 10% of your body mass). If you are purged of these cells, you die. This lack of microbial transfer was one of the reasons suggested for why infant mortality was so high in the years when babies were isolated from their mothers and other human contact upon birth.

http://www.amazon.com/What-Life-Lynn-Margulis/dp/0520220218

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