Life is only and exactly that which is at once conscious, sustainable, and evolving.
1) By 'conscious', what is meant here is sensitive to and responsive to the environment.
A rock is insensitive and unresponsive.
A single cell bacteria is.
One interesting consequence of this definition is that a virus by itself is not technically alive.
2) While the notion of consciousness applies to the individual, the notion of sustainable applies both to the individual and to the species.
In the individual sense, it is the ability to survive.
In the collective sense, it is in the capability to reproduce and in the overall persistence of the species.
3) The notion of evolution applies specifically to the species, rather than to the individual.
It is the aspect that life is not static but in a dynamic equilibrium with the environment.
Insofar as change is inherent, and environmental change is no exception,
the notion of evolution is effectively the species level ability to sense and respond -- it is the functional equivalent of an 'aggregate' consciousness.
Going further, the degree to which something is alive -- the degree to which a life or ecosystem is thriving
is therefore strictly proportional to the multiplicative product of the actual
degree of consciousness (awareness and responsiveness),
the degree to which there is a potential
to evolve, and the degree to which these two characteristics are actually
Finally, for those who are more technically minded,
note that the pattern of binding between the notions of conscious and unconscious, individual and group, actual and potential, all follow Axiom I and III patterns.
Also, that the observed transition process flow of 'life' as defined here, is consistent with dynamics outlined in Axiom II.
First level modality correspondences for Life are Consciousness as Immanent, Sustainable as Omniscient, and Evolution as Transcendent.
I understand this question as being similar to "Why does anything exist at all?",
Observationally, we can directly posit that between the two possibilities of 'existence' vs 'non-existence',
that the state of 'existence' is the universally 'preferred state'.
Why might this be?
Why is the potentiality of something existing preferred over the state of nothing?
Perhaps the answer is as simple as observing that the degree of potentiality associated with of anything existing
is in all cases strictly greater than the degree of potentiality associated with not existing.
From a purely information theoretic point of view,
insofar as the selection of multiple possibilities is always strictly more likely than one possibility,
then perhaps the state of being is universally preferred simply because its unbound range is infinitely more likely than the single state of non-being.
Among an infinite range of potential states,
the selection of the one singleton state of non-being is vanishingly small, and therefore itself non-occurring.
Being IS, and cannot not BE.