University:
Boston University
Course:
MET HI 215 | Special Topics in History
Academic year:

2022
Views:

221

Pages:

20
Author:

Alia Aguirre

Living fossils not really fossils—it’s just a metaphor Wollemi Pine Living fossils not really fossils—it’s just a metaphor A necessary condition? Proposal: Something is a fossil only if it is a geological item. Virtue: This explains why living fossils are not really fossils. A necessary condition? Proposal: Something is a fossil only if it is a geological item. Problems: 1. It’s not entirely clear what makes something a geological item. 2. Fossilization comes in degrees. Do these items belong to the geological record? Ambergris Bone breccia Problem case: Ambergris (“gray amber”) Produced in the intestines of sperm whales, perhaps to ease the passage of sharp objects through the gut. Often contains the beaks of giant squids. Undergoes some chemical changes, esp. oxidation, while drifitng at sea, becoming gray and waxy. An old age requirement? “A fossil is the remains of ancient life, but it is not practical to define a minimum age limit for fossils. Nevertheless, about 10,000 years before present is often taken as an arbitrary dividing line between what is fossil and what is Recent.” Motivation for the 10,000 year cut-off Every living organism is a trace of prehistoric life. The genes and proteins in all of our bodies contain information about phylogeny, about evolutionary rates and divergence points (as revealed by molecular clock studies). Are we all fossils? Absurd consequences? DNA obtained from a mammoth carcass >10 kya is a molecular fossil But DNA from the thylacine <100 years old is not. The difference between 100 ya and 10,000 ya is geologically trivial. Absurd consequences? Worse, should we say that the mammoth DNA, 5,000 years ago, was not (yet) fossil material, but that it became fossil DNA with the passing of time, in the absence of any other physical transformation? Literal vs. metaphorical usage Literal fossils Metaphorical fossils But what about …. Molecular fossils? Chemofossils? A puzzling case: Fossil water The term evokes an analogy with fossil fuels. But fossil water has inorganic (glacial) origins. Is this a metaphorical use (like “living fossil”) or a literal use of the term “fossil” in a different sense? Could fossil water be a pseudofossil? Linguistic fossils (These are just fun to think about.) If I had my druthers … To give something short shrift … … hoisted by one’s own petard The words “druthers,” “shrift,” and “petard” never occur outside the context of these phrases. The problem of multiple casts Is a human-made cast of a fossil still a fossil? The Carnegie Diplodocus (on the right) What if multiple casting & molding happened naturally? Therefore, The concept of a fossil is something of a mess. A dismissive response Because “fossil” is not a theoretical term, very little is at stake here. This is not like the terms “species” or “fitness,” which figure centrally in evolutionary theory. But paleontologists do theorize about fossils. Taphonomists test generalizations about them. Fossilization is an unobservable historical process. Other possible responsesto all this (1) Try to clear up the conceptual confusion. One approach: Go pluralist, distinguishing different senses of “fossil” appropriate to different contexts. (2) Tolerate, or even embrace, the conceptual confusion. We don’t know what fossils are, and that is not such a problem. The costs of clarity One can achieve clarity by means of revisionary proposals. For example: a fossil (broad sense) = any presently observable evidence of past life. But this would involve broadening the meaning of “fossil” beyond recognition. What makes the confusion tolerable? Paleontologists are largely interested in identifying and explaining patterns in the fossil record, i.e. in large samples of fossil data. Pattern/process inference does not require conceptual clarity about what fossils are. It just requires having a lot of them. An imperfect analogy The fossil concept plays somewhat the same role for paleontology that the concept of life plays for biology. There are relatively few scientific contexts where a precise definition of “life” is needed (e.g. astrobiology).