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Introduction

There has been a lot of talk recently about various aspects of artificial life - artificial intelligence, sentient machines, computers gaining self-awareness, and so on.

It seems self-evident that we can easily distinguish between living and non-living matter.  What I would like to argue here is that it is also easy to distinguish between real life and virtual life.  So – let's start with describing real life.

Living Organisms

A Description

We can’t say exactly what ‘life’ is, because life is an abstraction – but we can describe what a living organism is, because that is a real thing (many real things) which can be observed.  So let's start with a fairly obvious statement.

• A boundaried physical system which is capable of reproducing in the right environment is a living organism.

(This is elaborated in 'More Precisely' below.)

It is a physical system. Let’s not get confused at this stage with questions about the possibility of virtual life and sentient AIs: every living organism we have encountered to date has been physical in nature.

It is a boundaried physical system. Without a clear boundary, we can neither recognize an organism nor tell when it has reproduced.

It can reproduce. Reproduction is the most fundamental characteristic of life; all the other commonly identified characteristics of life only matter because they are needed in order for the organism to reproduce.

It must survive.  The organism must survive for as long as is required in order to reproduce: this differs from one organism to another.  Some organisms (like salmon and octupi) die after reproducing, while other organisms (like humans) need to care for their children - or even their grandchildren - to ensure their success.

Sex and survival are the two basic activities of all living organisms.

Attributes

Every living organism hs certain attributes: it feeds, it has feelings, it has desires, and it has purpose.  How does a complex computer or AI compare?

It feeds.  Food is not just a source of energy: the organism takes part of the environment, and turns this food into itself.  A computer can be said to 'feed' upon the electricity supplied to it, but this electricity does not become transformed into the electrical components it is made of.  And every living organism has specific food needs: a Koala will eat Eucalyptus leaves, not Sycamore leaves.  Feeding and processing the food are very significant activities for any living organism: much of its activity consists of feeding and processing the food, then using the nutrients obtained from the food to grow and replace cells.  No mechanical or virtual device engages in anything at all comparable.

It has feelings.  The organism feels its environment - that is, the environment changes it in ways it can detect; it also feels its internal state, and these are not entirely distinct activities.  A living organism feeling the temperature or tasting the food is quite different from a machine receiving a data feed containing a number which represents the temperature, or a chemical analysis indicating the constituents of the food.  Some feelings are neutral, but many feelings are good (ones which are desired) or bad (ones which are avoided).  The organism feels good when it feeds, and feels hunger if it does not feed; it also sometimes feels pleasure and pain - if not as we understand them, then at least to the extent possible for its level of development.

It has desires.  The organism wants to have the good feelings and it wants to avoid the bad feelings.  These desires are inherent, not imposed; they are built into the fabric of its being.  A machine cannot want to survive: it can only act in a way to preserve its integrity if it is instructed to do so.

It has purpose.  Every living organism has two basic built-in purposes: sex and survival - it aims to reproduce, and to survive until it has reproduced.  And it acts with purpose, which is not only about sex and survival directly, but also about satisfying its desires.  Again, these are all innate, buit-in to every cell of every living organism.  In comparison, a machine, computer or AI can only seek to do what it is instructed to do: it may be said to have a purpose, but that purpose is given to it - the purpose does not arise from within.

Full Life

All of this discussion is about the things which characterize real life, as opposed to artificial or virtual life.  It does not attempt to describe everything which living organisms are capable of.  At one point, Jesus talks about 'life in all its fullness', which we can reasonably assume encompasses much more than just feeding well, finding pleasure and avoiding pain.  In fact, His teaching and example shows that it is possible to transcend these concerns - perhaps not completely, and not all the time, but they do not have to control our lives.  However, such considerations are not part of this article.

More Precisely

A boundaried physical system which is capable of reproducing in the right environment is a living organism. Other similar boundaried physical systems are also living organisms, despite being sterile. There are four basic reasons why a living organism may be sterile:

• it may be damaged in some way;
• it may suffer from genetic errors;
• it may have been produced by an attempt at reproduction between living organisms which cannot produce fertile living organisms; or
• it may help other living organisms to reproduce.

Some parts and products of living organisms can be alive without being a living organism.  For example, a gamete (such as a human egg or sperm) can be alive, but is not itself a living organism; an organ which is to be transplanted into another body can also be alive, but is not a living organism.  Viruses are also products of living organisms, albeit products which have hijacked some part of the organism in question.  In all these cases, it is simple to tell the difference between a living example and a dead one.

So, within this framework, it is reasonable to describe a viable virus as being alive. But people do like to argue about whether viruses are alive.  It seems to me that the question is ultimately unimportant: you can define 'alive' in whatever way is most convenient for the context in which you are working.  They are not living organisms (as described above); on the other hand, they clearly belong to the 'living matter' category - they can be killed, and in a universe without life, viruses could not exist.

We said that "Sex and survival are the two basic activities of all living organisms" but, if we are being precise, then it is reproduction rather than sex: sex is only the mechanism of reproduction for complex living organisms, while the simpler ones are content to reproduce by cell division.  And we have already noted that there some living organisms are sterile.  So a more accurate, but less alliterative, statement would be, "Reproduction and survival are the two basic activities of all non-sterile living organisms."

One final technicality: it is clearly the case that some people choose not to reproduce, and some people are not allowed to reproduce.  The point is that these people (these 'living organisms') all have these two fundamental drives - sex and survival.  We can choose to die, and we can choose to be childless, but the fact that we can over-ride these drives does not mean they are missing or unimportant.

Notes

The awkward language is deliberate: I suggest that "A boundaried physical system which is capable of reproducing in the right environment is a living organism," rather than the more straightforward "A living organism is a boundaried physical system which is capable of reproducing in the right environment" precisely because this is not - and does not attempt to to be - a full definition of living creatures.  It is a description (enabling us to recognise a living organism), not a definition.

Sara Imari Walker (like NASA) defines life as "a self-sustaining chemical system capable of Darwinian evolution", but this is problematic in several ways - please see the New Scientist article, "How a radical redefinition of life could help us find aliens".  Apart from any other consideration, it should be obvious that no life is self-sustaining.  But at least they recognize that it is a chemical system, implicitly ruling out virtual creations.

George Musser in "The Biologist Blowing Our Minds" about Michael Levin "uncovering the incredible, latent abilities of living things" is worth a read; possibly the most relevant part addresses the question, "Why don't robots get cancer?"  A key observation - "The robot may or may not be intelligent to some degree, but at the next level down, all the parts are passive; they don’t have any goals of their own."

Jensen Suther's article in the New Statesman, 'Hegel against the machines', describes several earlier expressions of the view expressed here that intelligence is an attribute of life, so machines (non-living mechanisms, whether mechanical or electronic) cannot think or be intelligent.  Dreyfus ('What Computers Can’t Do', 1972 and 'What Computers Still Can’t Do', 1992) and Haugeland ('Artificial Intelligence: The Very Idea', 1985)  are reasonably well known, but Suther points out that Hegel identified the issues even more clearly in works such as 'The Science of Logic' back in 1812.