Well, I have been taken to the woodshed by my many geologist friends for using the word “geologist” to describe those who use the Periodic Table to guide their expectations, which in turn are key to deciding whether or not a result is viewed as “extraordinary”, in the Sagan sense.
My bad. And to think of it, more correct for such folks would be the word “chemist”. After all, the Periodic Table is at the core of chemistry. Further, those whose work in geology departments centers on the Table might call themselves “geochemists”, to distinguish themselves from those whose work centers on hiking landscapes to plot strata.
Now, anyone who finds the string c-h-e-m-i-s-t somewhere in their CV does not a priori find it absurd to propose that an element below another element in the Table might substitute for an element above. Especially organic chemists. Indeed, the “halogen series” of compounds (fluorine replaced by chlorine replaced by bromine replaced by iodine) is a staple of physical organic chemistry; the changing reactivity of one set of compounds along that series is used to calibrate changing reactivity for many other sets.
This is even true for elements in the middle of the Table. People who base expectations using the Periodic Table (shall we call them X-chemists?) do not discard generally as absurd the notion that silicon might substitute for carbon in some contexts, or arsenic might substitute for phosphorus, with “trend-like” changes in behavior.
But Sagan’s aphorism (“extraordinary claims require extraordinary evidence”) was the focus of my comment, not the naming of fields. It is not easily applied, as “extraordinary” depends on context. If all that you know about chemistry is the Periodic Table, the claim of arsenate DNA might not strike you as requiring extraordinary evidence. Only if you know much more chemistry does this change.
As a short follow up, lots of blogs are using the word “heresy” to describe the proposal that the DNA in GFAJ-1 contains arsenic at spots instead of phosphorus. It is not heresy; it is just a hypothesis, and can be tested like any other.
Arsenic DNA was back in the headlines in May , as Science published eight critical comments, one editorial, and a reply from the authors of a report from last December  that concluded that a microbe (GFAJ-1) had DNA with some of its backbone phosphorus atoms replaced by arsenic atoms. But that report had already entered the curriculum of science education, where courses on the philosophy and history of science at schools as diverse as the University of Chicago and East Side High School in Gainesville, Florida, pondered what the report of arsenic DNA showed about how science works.
The technical details will be lost on most students. However, even high school students can perceive the form of the arguments being made in this collection of pieces. They center on where “burdens of proof” lie in science and what “standards of proof” should be.
Continue reading ‘Does Arsenic Really Exist in the DNA from GFAJ-1?’ »
Many languages have words and phrases, called contranyms, that have two nearly opposite meanings. For example, a “citation” from Harvard University is good, but a “citation” from the Harvard University police is bad. If you run “fast”, you are moving at great speed; if you hold “fast”, you are not moving at all.
“Synthetic biology” is a contranym. In a version popular today in some engineering communities, “synthetic biology” seeks to use natural parts of biological systems (like DNA fragments or protein “biobricks”) to create assemblies that do things that are not done by natural biology (such as digital computation or specialty chemical manufacture). Here, engineers hope that the performance of the molecular parts drawn from living systems can be standardized, allowing them to be mixed and matched to give predictable outcomes, just as an electrical engineer can assemble standardized transistors to give integrated circuits with predictable performance.
Continue reading ‘What is Synthetic Biology?’ »