Is it Alive? Exploring the Boundaries of Life

1. Is it Alive? By Will Pierce I400 Spring 2007

2. A difficult Question • Many possible definitions • Each seems to exclude some living things while including non-living ones • Fundamentally limited by our lack of experience with life outside Earth • Carbon-and-water-based life is all we know

3. Conventional Definition(Wikipedia) • Homeostasis • Self-regulation of internal temperature • Organization • Composed of one or more cells • Parts are interdependent • Metabolism • Consumption and conversion of non-organic material into energy • Growth • Both individual organisms and species population will grow in response to an abundance of energy

4. Conventional Definition(Wikipedia) • Adaptation • Individual organisms adapt to circumstances and environment • Population as a whole evolves due to natural selection • Response to Stimuli • Ranging from very simple to very complex • Reproduction • Species population is able to autonomously expand via sexual or asexual reproduction

5. Problems • Not all living organisms conform to all of these specifications • Classic example: The Mule, a genetic hybrid, is clearly alive but not able to reproduce • Viruses are unable to reproduce without a host • Certain ‘castes’ of insect species (i.e. worker ants) are sterile • Some non-living phenomena could be encompassed by these criteria • Fire can grow, reproduce, adapt to its environment, convert surrounding material into energy, maintain its internal temperature, and basically do everything else on the list • Computer programs can be made to perform most of the above functions as well

6. Farmer and Belin • Life is a Pattern in Space-Time • Rather than a set of physical characteristics • Autonomous reproduction, if not in the organism itself, in a related organism • Covers mules, viruses, and worker ants • Storage and interpretation of a Self-image • Example: DNA (genotype) is interpreted by RNA to define an organism’s characteristics (phenotype) • Metabolism • Organisms such as viruses can make use of a host organism’s metabolism

7. Farmer and Belin • Functional Interactions with the Environment • Interdependence of Parts • Stability Under slight Changes in Condition • Evolution

8. Alternative Definitions • Schroedinger: Negative Entropy • Life maintains a low level of entropy by ‘exporting’ entropy • Entropy, as defined by the Second Law of Thermodynamics, states that in a closed system, all objects’ energy will move towards equilibrium • Living things derive a net increase in energy from their environment

9. Alternative Definitions • Stuart Kauffman’s “Systemic” definition • Autonomous agent or multi-agent system capable of completing at least one thermodynamic work cycle • Self-organizing and self-producing (autopoietic)

10. Still Problematic • All of these definitions, while insightful and generally workable, leave something to be desired • A mule, worker and, or virus would be “less alive” than an intelligent robot, by some criteria • Forces us to attempt some sort of physical definition (i.e. carbon chains) • Or we can adapt our definition to include certain forms of artificial or man-made life

11. More Problems • Some criteria are too specific • Example: “genotype is separate and different from phenotype” • Applies to most but not all organisms • Example: Prions, a special type of virus, are mad up of a single protein, which carries both their genotype and phenotype • This can be misleading • Biochemical or thermodynamic definitions tend to exclude automata or computer intelligence, which are considered by some to be alive • Also excludes theoretical or extraterrestrial life that we have not yet encountered

12. Highly Subjective • Dependent upon individual values and schemas • Can man-made entities truly be alive • Computer intelligence • Robots • Clones or genetic hybrids • Or are these just simulations of life? • Heavily dependent on personal values and prejudices

13. Middle Ground • Some properties can be universally agreed upon • Response to stimuli, adaptation, self-organization • Not all criteria satisfied by all life forms • But we can all agree that a mule or a worker ant is alive despite inability to reproduce • Many non-living things satisfy some of our criteria • But we can all agree that fire is not alive, despite its ability to grow, adapt, maintain homeostasis, metabolize non-organic material, etc.

14. Intuitive • For lack of a better terminology, we could say that we “just know” if most things are alive • Obviously there are grey areas • Hence the study of “theoretical life”, “artificial life”, etc.

15. Study the Fringes • Most biological life can be easily categorized and defined by reasonable criteria • Theoretical life studies the oddities, exceptions, and borderline cases • These cases help to further our understanding and expand our thinking about what constitutes life • If we can assimilate these difficult cases into a unified definition of life, we can eliminate some of the confusion

16. Conclusion • It seems nearly impossible at this point to come up with an all-encompassing definition of life that everyone can agree on • Best to agree on the most common characteristics, which define most life as we currently know it • Deal with the exceptions on a case-by-case basis