Paul Nurse

What is Life?

“Life is constantly experimenting, innovating and adapting...”

What is life? What is is not life? What is a meaningful life?1

Sir Paul Nurse (b. 1949), a Nobel Prize-winning geneticist, neatly answers a fundamental yet baffling question: what does it mean to be alive?

It begins with cells.

I saw my first cell when I was at school… My class had germinated onion seedlings and squashed their roots under a microscope slide to see what they were made from. My inspirational biology teacher, Keith Neal, explained that we would see cells, the basic unit of life.

And there they were: neat arrays of box-like cells, all stacked up in orderly columns. How impressive it seemed that the growth and division of those tiny cells were enough to push the roots of an onion down through the soil, to provide the growing plant with water, nutrients and anchorage.

As I learned more about cells, my sense of wonder only grew. Cells come in an incredible variety of shapes and sizes…If you had a egg for breakfast, consider the fact that the whole of its yolk is just one single cell.

The cell, Nurse instructs us, is the basic unit of life just as the atom is the basic unit of matter. Life is unexpectedly modular: everything that is alive on the plant is either a cell or made from a collection of cells.2

Photograph of Sir Paul Nurse. Featured in Nurse's "What is Life" in the Examined Life Library.
In 2001 Nurse won the Nobel Prize in Medicine for determining the molecules responsible for cell regulation and reproduction. Learn more.

If a cell is, among many other things, the engine of life, its most unique property is its form.

A critically important part of a cell… is its outer membrane. Although just two molecules thick this outer membrane forms a flexible ‘wall’ or barrier that separates each cell from its environment, defining what is ‘in’ and what is ‘out’.

Both philosophically and practically, this barrier is crucial. Ultimately, it explains why life forms can successfully resist the overall drive of the universe towards disorder and chaos. Within their insulating membranes, cells can establish and cultivate the order they need to operate, whilst at the same time creating disorder in their local surroundings outside the cell.

When I contemplated What is a Wall? I never imagined a wall would have properties of life itself.

Another philosophical player are genes. In a universe that tends towards flux, “life is constantly experimenting, innovating and adapting” to quote Nurse, the genes create continuity of being. A series of traits passed on, occasionally adjusted, are responsible for every iota of life on earth.3

Over aeons of time, different species have rise to prominence, their forms changing beyond recognition, as they have explored new possibilities and interacted with different environments and other living creatures. All species – including our own – are in a state of perpetual change, eventually becoming extinct or developing new species.4

Bird nest. Featured in Paul Nurse's "What is Life?" in the Examined Life Library.
Pigeon nest and eggs found outside our apartment. The yolk of an egg is a single cell. Photograph by Ellen Vrana.

Our little cell, charged as the building block of life as well its blue-print messenger, also leads to the expression of life.

It is actively communicating to everything around it. Think of the cell as an extremely extroverted person, one who talks, connects, receives, talks more and connects even more.

The cell is a social hub.

Information is at the centre of all life. For living organisms to work effectively as complex, organized systems they need to constantly collect and use information about both the outer world they live in and their internal states within. When these worlds – either outer or inner – change, organisms need ways to detect those changes and respond. If they do not, their futures might turn out to be rather brief.

This vast communication system delivers some predictability to life’s existence, propagation and extinction. It also means that geographically, vertically up and down the food chain, and throughout eras – all life is interconnected at the cellular and genetic level.

Wislawa Syzmborska’s glorious and perfect poem “Microcosmos:”

The glass doesn’t even touch them,

they double and triple unobstructed,
with room to spare, willy-nilly,

To say they’re many isn’t saying much.
The stronger the microscope
the more exactly, avidly they’re multiplied.

They don’t even have decent innards.
They don’t know gender, childhood, age.
They may not even know they are – or aren’t.
Still they decide our life and death.

from “Microcosmos”

Alan Lightman surmised we are made of stardust and questioned how that stardust amounted to life. Biologist Rachel Carson warned that our biological interconnectivity is the key to understanding our environment and ourselves. And let us not forget emotionally generous Walt Whitman who assured mankind that “every atom belonging to me as good belongs to you.”

So, what is life? Well, the next time you hear a report of “Evidence of life on Planet X” ask:

Are there bounded cells?
Do the cells reproduce through a variable hereditary system?
Do the cells have a metabolism to survive, grow and reproduce?
Are these systems co-ordinated and regulated by information flow?

Or simply hold this magnificence in the palm of your mind and conceive your complexity (but do not omit to thank your little cells for making that contemplation possible).