Core argument: "life" is not a natural kind, and so investigating its nature is misguided.
Guiding questions: What is the relationship between life on Earth & life in general? How should we think about life in general?
What kind of a class is Life? There's a spectrum with "Natural Kinds" on one end (ex: "gold:" a gold coin is more like a gold bar than like a silver coin), other end is "Arbitrary Groupings" (ex: cabbages and kings, no real logic to join them).
(I am reminded of the category errors made by the Presger rep in @ann_leckie's Ancillary Mercy. The captain minus her leg is not the captain anymore. What makes one set of objects into a meaningful whole?)
A less-arbitrary thing on the scale of concepts: "property clusters." Defined by co-occurring properties that tend to appear together.
Aha I anticipated his talk! "Two legs" was one example of property cluster definition of humans: it's usually co-occurring, but not actually necessary.
"Stable property clusters" & "Conventional property clusters" as the two things in the middle of the scale (Natural Kind, Stable Cluster, Conventional Cluster, Arbitrary). Our speaker thinks life is more a Conventional Cluster.
The distinction between Stable Cluster & Conventional Cluster I missed, but the examples seemed to include "owls" as Stable, "games" as Conventional.
Distinction between classes (which have shared properties) and individuals (distinguished by continuous history). Classes can recur, exist without instances, made up of elements/sub-classes.
Whereas individuals don't have defining properties! You can change any/all properties and still remain the same individual. Compare babyhood vs adulthood. "4yo me didn't know ANYTHING about philosophy!"
A big move in 1970s philosophy of biology was to start thinking about species as individuals instead of classes. They start & stop existing, with a continuous history.
If species are individuals, their names are proper (capitalized), they don't have defining properties, and organisms are parts not members!
I like that last thought - "organism as part, not member, of the species." It's one of those thoughts that seems trivial/obvious but only in retrospect, which IMO is sign of a really good insight
The species is composed of (rather than exemplified by) its organisms. If I understand correctly.
Problem cases, of course. RNA world before DNA? Viruses? Synthetic biology? Artificial life? (Computer simulation of life: is that life, just in a different substrate?) Alien life?
Defining the class that is life (lowercase L because it's not an individual)... think about the Darwin/Haldane/Aristotle/etc distinctions from the last talk, each of them is a scale of "how good fit?" Problem cases (e.g. viruses) fit differently under different definitions.
3d continuum of life. Axes: complexity, metabolism, evolution by natural selection. Things fall in the cube. Being high on all 3 is obvious/classical life. But there are so many weird cases.
New findings might not cluster neatly around anything we know. (Earth life has weird clusters already: if you look at pressure/temp/pH ranges, we don't fill a sphere, we fill a wonky complex space.)
The question "is this life?" is answered not by observation, but by decision!
Capital-L Life (individual) as all known life on earth descended from common ancestor. Lowercase-l life (class) as anything we decide is relevantly similar to life on earth.
Q&A quote: "The thing about life on Earth is there's a huge difference between a pigeon and a rock!" The point being that biocentrism does work pretty well when you're restricting yourself to everyday-Earth stuff.
Oooh, interesting question in Q&A. "Are individuals and classes natural kinds?" You can start your individual story at some point in childhood, at conception, at ancestors. It's not clear.
An individual can contain other individuals. (Easy example: an organ can be seen as an individual - your stomach is more different from your liver than one human is from the next.)
Important note: Life is the stuff on earth with common ancestRY, not ancestOR. We don't need to know the First Common Ancestor (First Darwinian Population) or anything like that.
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