chyba def

Attempted definitions of life: 

Attempted definitions of life Thermodynamic (but crystals etc.) Metabolic (but fire, and lessons from Viking) Biochemical (but too restrictive?) Genetic (but see problems with 'Darwinian definition' below) Etc. (but etc.)

Slide2: 

Viking biology package: 

Viking biology package Searches for metabolism Labeled release: life on Mars? 'if information from other experiments . . . had not been available this set of data would almost certainly have been interpreted as presumptive evidence for biology' (Klein 1978) GCMS: No organics to limits of sensitivity (ppm to ppb) in stepwise heating to 500 C de facto search with a biochemical definition: Is biochemical definition trump? ('No organics = no life')

Slide4: 

Viking biology package: 

Viking biology package Searches for metabolism Labeled release: life on Mars? 'if information from other experiments . . . had not been available this set of data would almost certainly have been interpreted as presumptive evidence for biology' (Klein 1978) GCMS: No organics to limits of sensitivity (ppm to ppb) in stepwise heating to 500 C de facto search with a biochemical definition: Is biochemical definition trump? ('No organics = no life')

The (chemical) Darwinian definition: 

The (chemical) Darwinian definition 'Life is a self-sustained chemical system capable of undergoing Darwinian evolution' 'Darwinian': Reproduction, mutation, natural selection 'Self-sustained': contains all genetic information necessary for its own metabolism Laboratory utility 'The origin of life is the same as the origin of (Darwinian) evolution'

Computer “Life”: 

Computer 'Life' 'Chemical Darwinian' definition excludes computer life by fiat In a functionalist view (Darwinian evolution is a process that can be abstracted from physical details) computer life is life (Computer substrate analogous to lab glassware) Computer is not said to be alive, but rather the processes themselves

“Life” vs. “A Living Entity”: 

'Life' vs. 'A Living Entity' An individual sexually reproducing organism does not evolve . . . so, e.g.: Victor Frankenstein (Shelly 1818) did not create 'life' by the Darwinian definition What will we detect remotely? 'Life' or a 'living entity'? (How do we recognize whether a system is 'capable' of Darwinian evolution?) Need a definition of 'living entity'? (Fleischaker 1990)

Is a Complete Definition Impossible?: 

Is a Complete Definition Impossible? Küppers (1990) quote Argument contradicted by RNA world?

Life as we know it: 

Life as we know it Liquid water Biogenic elements (H,O,C,N,S,P,…) Free energy Darwinian evolution?

The Nature of Definition: 

The Nature of Definition (Cleland and Chyba, Origins of Life, submitted) 'Ideal definitions' (necessary and sufficient) E.g. 'Bachelor = unmarried male': matter of linguistic convention, but inescapably vague 'Stipulative definitions' (precise technical meaning independent of ordinary usage) E.g. definition of triangle in euclidean geometry (closed planar figure with three sides)

Consider defining “water”: 

Consider defining 'water' Before molecular theory: inescapably vague Not just a matter of linguistic convention; rather 'defined' by reference to sensible properties (transparent liquid, odorless, tasteless…) Analogy to Koshland’s 'PICERUS'? (list of attributes)

“Life” vs. “water”: 

'Life' vs. 'water' Once molecular theory exists, identity is possible: Water is H2O Possible because water is a 'natural kind' with an inherent nature independent of properties humans use to recognize it) We do not have (will we ever?) an analogous theory for life Is life a 'natural kind'?

Life as we don’t know it: 

Life as we don’t know it Solvent other than water (Polar: ammonia? Nonpolar?) Si instead of C? (but standard objections, plus ISM data) Other forms of energy (Less radical: chemical disequilibrium but weird sources; more radical: altogether different approaches) Non-Darwinian evolution (Reproduction without replication? Lamarckian RNA world?)