Cletus the Foetus ♥'s puddles
Today, on my way to school, I was stopped at a corner, waiting for my light to change. The night had been cold, and yesterday's rain had frozen, but now that the sun was out everything was melting.
At my feet, a puddle was growing, fed by runoff coming from the Esso parking lot which lies only a couple of meters away, slightly up a hill.
I thought to myself, "If that puddle gets big enough, surface tension and the irregularity of the pavement are going to split it into two baby puddles. That's like asexual reproduction. And it's feeding from that runoff. So is the puddle alive?"
This, of course, led to hours of fascinating debate in the catbox, but there were too many issues that we were unable to resolve. So I went off in search of a textbook definition of life (as a biological process) by which I could determine whether a puddle is alive. After some searching around on the internet, I discovered that there isn't a whole lot of consistency in the definition of "life." So I've culled what I could.
–1:–
A Life Form is an organic whole.
The first thing to keep in mind is that a living being is organic. This philosophical term means that the entity in question is, as a whole, more than simply the sum of its parts. Modern computer science and artificial intelligence research use a similar concept: emergent phenomena. Life is a Gestalt, a holistic or synergistic or transcendental phenomenon. Organicism is a category of life.
–2:–
A Life Form can reproduce.
A living being can generate another, like being (another organic whole). Known life forms have various ways of doing this, including budding or other forms of asexual reproduction, as well as sexual reproduction (which includes endogamy as well as exogamy). In effect, if an organic whole can so much as split into two new wholes which have the same definitive nature as the parent, the entity has reproduced.
–3:–
A Life Form has metabolism.
Some scientists emphasize the conversion of energy from one form to another. Considered loosely, however, metabolism means the incorporation of outside matter into the form's mass. This may be a prelude to reproduction, adaptation, movement, or simply maintenance.
–4:–
A Life Form responds.
A living being can respond to its environment in certain ways. This can include locomotion, growth against force, homeostasis, whatever. The point is that the body undergoes some sort of motion as a result of something that happens in the environment but which is more than simply the application of brute force on the thing.
In addition to these fundamental or essential characteristics, most life (as we commonly recognize) exhibit certain tendencies. Most living things have highly complex forms, composed of many chemicals which interact in fairly regular ways. They also tend to regulate their own bodies (homeostasis). Metabolism generally involves the conversion of energy from one form to another (primarily potential to kinetic). According to some, an entity must move under its own power in order to be considered alive (viri cannot). Others emphasize that the energy conversions and transfers which constitute the organism's metabolism must be "purposeful" "behaviour" (words which cannot apply to automatic chemical reactions by any stretch of the imagination). In any event, while any or all of these alternative factors may play a role in a laboratory sample's life, they cannot be considered definitive.*
So, back to my original question: – Is a puddle a life form? Certainly it is an entity or unit – but then again, so is everything (literally every thing). However, is there anything about a puddle that is such that it has a nature that is more than just a given quantity of water? First we must define "puddle." What I was thinking of was a continuous mass of water (or really, any liquid) in a gravitational field, ideally on a flat surface but at least a non-convex surface. Insofar as a puddle, qua puddle, a unit that has a form more abstract than just a mass of water, it behaves according to laws distinct from those governing individual molecules or any amount of water under any other circumstances. So it is, after its own fashion, an organic whole.
What about the definitive characteristics of life? Can a puddle reproduce? Can it metabolize? Can it react to the environment? A puddle's size is determined either by the limits of concavity (ie., it fills a recess) or by the limits of its own surface tension (ie., it's too small to spread). Water that comes in contact with the puddle, such as from runoff, becomes part of the puddle thanks to cohesion. Non-water that comes in contact with the puddle will be "kissed" and surrounded if adhesion permits. If it receives "food" (ie., water), it will grow until it either comes up against one of the former limits, or it exploits the landscape in order to bud (ie., become two puddles).
This behaviour exhibits reproduction (by budding), metabolism of a sort (cohesion, incorporating "raw water" into its form), and response (adhesion). None of the secondary characteristics of life are present, but the essential ones are.
THEREFORE PUDDLES ARE ALIVE**
Sources:
http://www.ibiblio.org/jstrout/uploading/potter_life.html
http://www.geog.ouc.bc.ca/conted/onlinecourses/geog_111/7a.html
http://web.mit.edu/12.000/www/finalpresentation/experiments/life.html
* In addition to entities which conform to the basic definition of life (organic, reproducing, metabolizing, responding whole) but which we don't normally consider alive – such as fire or, as I shall show here, puddles – as well as those beings which we're not quite able to classify – such as viri and plasmids – there are entities which we would like to say are alive but which don't conform to certain aspects of the definition. The most confusing violation is the case of mules, who are "alive" but do not reproduce (though their cells do). What the hell is the deal there, anyway?
** Though I refrain from trying to determine whether they have souls.
Noder's Note (later): You know, on sober reflection, I suppose I should qualify my conclusion here. Certainly it was not my intention to give the impression that I think any old physical process or discrete unit of matter constitutes "life." Rather, I wanted to emphasize that life is process, and that similar processes can be seen in the most transient of phenomena – including the very short and tragic lives of rain puddles.