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ANTS and infertile humans are not alive, but parasitic DNA is. That鈥檚 the
view of a Polish researcher who has proposed a new, universal definition of
life.

He claims it will lay to rest arguments about what is and isn鈥檛 alive, and
might offer insights into when life on Earth got started. And if we ever find
something that looks like life on another planet, his definition could help us
settle whether it鈥檚 alive or not.

Bernard Korzeniewski of the Institute of Molecular Biology at Jagiellonian
University in Krak贸w, Poland, says that definitions of life usually list
the attributes an organism must have, such as genes, a certain level of
complexity, the ability to reproduce and evolve, and so on. But this, he says,
merely describes life rather than providing a useful way of deciding what鈥檚
alive and what鈥檚 not.

So Korzeniewski set out to formulate a fundamental definition of life, 鈥渨hich
would apply not only to life presently existing on our planet but also to the
first living organisms on Earth, as well as to life-like phenomena existing
presumably on other planets in the Universe鈥�, as he puts it.

His definition is this: 鈥淎 network of inferior negative feedbacks
subordinated to a superior positive feedback.鈥� In other words, it鈥檚 a system
that tries to regulate itself to preserve its identity.

It might not sound like much, but Korzeniewski is convinced that this broad
formulation鈥攚hich he calls a cybernetic definition of life鈥攑inpoints
the defining function of life, rather than listing its attributes. 鈥淚n spite of
the enormous diversity of life forms, the most fundamental principles of
biochemical construction and function are astonishingly alike,鈥� he says.

Under his definition, sterile worker ants are not alive because they rely on
others to reproduce and preserve their own identity. And although it would be
anathema to most people, he says the same applies to infertile humans. But an
ant colony is a living system, according to Korzeniewski, because individuals
work together to preserve the colony as a whole. 鈥淎n ant is alive in the manner,
say, a liver or a heart is鈥攐nly as a part of some bigger system,鈥� he says.
Individual ants may be complex systems, but complexity is not unique to
life鈥攋ust look at computers.

Similarly, viruses, cancers and parasitic DNA that has no function but gets
passed down the generations, all count as alive. All are capable of producing
regulatory enzymes that ultimately help them reproduce. But prions and
viroids鈥攄isease-causing particles of RNA smaller than a virus鈥攄o not
have this ability, and should not be considered alive.

One reason why life is such a great mystery is that no one has yet been able
to define it, says Mark Bedau, a philosopher of biology at Reed College in
Portland, Oregon. Bedau welcomes the generality of the new definition. 鈥淏ut the
test of a good definition of life is whether it can settle ambiguous cases,鈥� he
says.

Korzeniewski says his definition also pinpoints when life emerged. He
believes life began with RNA鈥攖he first molecules capable of perpetuating
their identity through replication.