Newsletter #178 What is life? And is that a question for a biologist?
Newsletter about nature and science
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What is life? And is that a question for a biologist?
It might seem a bit strange, because a biologist literally studies life. So you would expect them to know the answer… Even though most people have a general sense of what life is, it’s actually not an easy question to answer. According to some, reproduction is an essential characteristic of life. But then, does a neutered dog not count as alive? All living things are made of cells—but is that enough as a definition? Dead cork tissue also consists of cells, after all.
At school, you probably learned the seven characteristics of life—do you still remember them? But even those have limitations and certainly don’t apply to the entire life cycle. And what about viruses? Most biologists would draw the line there, as a virus always depends on other life forms to function. That one simple, all-encompassing definition of life seems far away. But is that a problem?
Perhaps not. It also depends on the perspective from which you approach life. Take thermodynamics, for example. From a physics perspective, life could be described as a temporary resistance against the law of increasing disorder (entropy). A chemist might mutter something like: “a combination of many different chemical systems that together are more than the sum of their parts” (as Nobel Prize winner Ernest Rutherford once suggested)
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Life is often described based on what a living system must do and be able to do. The core elements are that order must be maintained within the (cellular) body, and that there must be an exchange of substances and energy with the environment. Growth and development must also take place, along with responses to external stimuli. An environment to which the life form can adapt. That sounds a lot like the list of seven you learned in school:
breathing, feeding, excreting, moving, growing, sensing, and reproducing.
The challenge is that a definition of life should ideally draw a clear boundary that applies to all life forms—plants, animals, fungi, algae, and bacteria. And that’s only the life we know of on Earth. What about extraterrestrial life? We can only speculate about that for now. We are made of stardust, but that doesn’t tell us very much either.
In the end, it may be more interesting to look at how life develops. The interaction of chemical compounds leads to the formation of complex molecules, as we also see in viruses. And to their credit, viruses are perfectly capable of reproducing and surviving—although they always need other life forms to do so. Independence is the next step, and the formation of a cell—and later multicellular organisms—was certainly a major one.
And so, we can describe the entire Darwinian evolution of life forms, which, at least for life on Earth, has resulted in a remarkably robust and well-founded framework. All in all, chasing after one conclusive definition of life is of limited satisfaction—though perhaps inspired by the question of what happens when death enters the picture.
The question of how life on Earth actually began is at least as intriguing, but we’ll save that for another time.
Five prompts to reflect further on what life is:
What makes the difference for you between something being alive or not?
And what exactly changes at the moment of death?
What do you think alien life would look like?
An inspiring article from the NEMO science museum (in Dutch):
https://www.nemokennislink.nl/publicaties/je-herkent-leven-als-je-het-ziet-maar-wat-is-het/
Or check out NASA’s resource:
https://astrobiology.nasa.gov/research/astrobiology-at-nasa/exobiology/
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