The question "what is life for science?" is examined at the light of the theory of autopoiesis by
Maturana and Varela, which puts the emphasis on the behaviour of the biological cell. The apparent
paradox between the cell auto-maintenance and the myriads of ongoing transformations
inside the cell, is solved by the observation that the cell re-generates from within its boundary
all components that are going to be consumed away during metabolism. The capability of selfgeneration
from within is taken as the most general and most important characteristic of life in
general. This process of self-generation is possible thanks to the interaction with the environment,
and this brings us to the notion of cognition. All living organisms, including bacteria, are cognitive,
in the sense that they are provided with the sensorial tools to recognize and interact with
their own specific environment. For humans, cognition takes the form of the five senses, plus the
mind, so that the final answer to the question "what is life?" is the trilogy of the autopoietic unit,
the environment, and cognition, which are intrinsically linked to each other in a single unity.