Biologists Still Cannot Agree on What Life Is
Life is the condition distinguishing living things from inert matter. No definition covers every case.
Life is the condition that distinguishes living organisms from inert matter. Defining it precisely has defeated biology: the usual checklist of growth, reproduction, metabolism and response to stimuli excludes mules, which do not reproduce, and admits fire, which grows and consumes fuel. Viruses sit awkwardly outside most definitions while clearly not being inert. *Life* is Old English, and the plural *lives* follows the same F to V pattern as *knife* and *wife*.
- The living state. *Signs of life.*
- A lifetime. *All his life.*
- Vitality. *Full of life.*
- Alive — the adjective. *Alive.*
- Old English — *lif*. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | life | Life. |
| Plural | lives | Lives. |
| Adjective | alive | Alive. |
| Adjective | lively | Lively. |
| Old English | lif | Life. |
- There was no sign of life.Existence.
- She lived a quiet life.Lifetime.
- Viruses are a hard case.Biology.
Why life resists definition
- Mules do not reproduce, yet are plainly alive
- Fire grows and consumes fuel, yet is not
- Viruses replicate but only inside a host cell
- Crystals grow and can seed copies of themselves
- NASA uses a working definition for its own purposes rather than a settled one
Old English *lif*, of Germanic origin, related to Dutch *lijf* and German *Leib*.
Why is life hard to define?
Every checklist either excludes something clearly alive, like a mule, or admits something clearly not, like fire.
Are viruses alive?
There is no settled answer. They replicate and evolve but only inside a host cell, and lack metabolism of their own.