Here's where we get to some interesting questions on what is life.
Chapter 2 - Question 3
Is an apple – hanging on a tree – living? When it falls to the ground – is it still living?
This isn't a silly question
Wow, now we get to the meat of it. And this is where I start to have fuzzy thoughts on the subject. It all depends on how you define ‘life’. If reproduction is a requirement for life, then the cell in the apple are probably alive, but the apple itself is not. The seeds are the result of reproduction in the parent tree, not in the apple it self.
This article relates an interesting story about that.
What is the definition of life? I remember a conference of the scientific elite that sought to answer that question. Is an enzyme alive? Is a virus alive? Is a cell alive? After many hours of launching promising balloons that defined life in a sentence, followed by equally conclusive punctures of these balloons, a solution seemed at hand: “The ability to reproduce—that is the essential characteristic of life,” said one statesman of science. Everyone nodded in agreement that the essential of a life was the ability to reproduce, until one small voice was heard. “Then one rabbit is dead. Two rabbits—a male and female—are alive but either one alone is dead.” At that point, we all became convinced that although everyone knows what life is there is no simple definition of life.
To use the classic definition of life that I was taught many, many moons ago. Life has these characters: Composed of cells, has metabolism, grows, adapts, responds to stimuli, reproduces, and maintains homeostasis.
I kind of like that definition, but an apple is not alive by this definition. The cells within it are, but the apple itself does not grow, reproduce, respond (except chemically), or has a metabolism.
Can we separate the living thing from the cells it is composed of? i.e. if the cells reproduce, does the organism? If the cells retain metabolism, does the organism?
I ask because a dead organism may have most of its cells function even after the organism itself dies… at least for a little while.
Which brings us to another question, that maybe we should consider first.
Chapter 2 - question 1
Do you believe in the utility attempting to give a definition of life?
I do think that there is utility in dealing with this question now. Avida organisms can already evolve complex logic functions. And computers are beginning to approach the computing power of the brain (cat brains first) and the human brains processing abilities. (I will note that there is some skepticism on whether IBM has actually reached the equivalent computing power of a feline.) With that in mind, the question of what is alive will become very important… or maybe not. Humans have an unfortunate tendency to use resources and organisms regardless of the ethical considerations involved.
Life is like porn (you knew I was going there right?). We might not be able to define it, but we know it when we see it... or do we. Avida organisms are something that's pretty close to any reasonable definition of life, but they are definitely not made of cells. Could there be other non-cellular life that we would just ignore because we don't see cells?
So what are the qualities that life must have to be considered life?
Honestly, I've been thinking about this for several months (in those 12 seconds between when I can finally lay down and when I actually go to sleep... otherwise known as 'spare time'). It is extraordinarily difficult to develop a definition of life that does not have some exception. The apple above for example. Combinations are even trickier.
I have placed an additional burden in that I think that digital organisms could eventually be alive.