What exactly is “life”? Astrobiologists still have more questions than answers
What exactly is “life”? Astrobiologists still have more questions than answers
By Dirk Schulze-Makuch | Published: 2025-08-12 18:41:00 | Source: Hard Science – Big Think
Sign up for Big Think on Substack
The most surprising and impactful new stories delivered to your inbox every week for free.
Defining exactly what we mean by “life” – in all its diverse forms – has long been an enormous challenge. Physicist Erwin Schrödinger wrote a book called What is life? In 1944. More than 80 years later, despite all the progress we’ve made in biological sciences (including discovering the structure of DNA), we still don’t have a definitive answer.
None of the many definitions proposed have been widely accepted. It seems that almost every researcher in this field has a favorite one. the The latest discovery was made by Ryo Harada of Dalhousie University and colleaguesA microorganism with a genome so small that, in essence, it contains only enough genes to replicate, only adds to the complexity.
The archaea involved (Sukunaarchaeum is a miracle) lives inside another organism and appears to be something between a virus and a bacterium. According to the traditional dictionary definition, “life” requires metabolism, growth, replication, and adaptation to the environment. Therefore, most scientists do not consider viruses to be alive because they cannot reproduce and grow on their own and do not metabolize. However, they possess a genetic mechanism that enables them to reproduce with the help of a living cell.
Parasites also cannot reproduce without a host, but no one can say that an animal like a tapeworm is not alive. Strictly speaking, viruses fit into conventional standards of life only part of the time, and under certain conditions. What’s even more confusing is that Viruses may have evolved from bacteriawhich clearly We are alive. Is this the case in which a living organism turns into a non-living state due to evolutionary pressures? If so, where do we draw the line between living and non-living? Is it more of a continuum than the clear dividing line many of us expect?
Life as we might find it
Because astrobiologists think not only about life as we know it, but also about life as we know it You may find itSome of them gravitated toward the broad definition of life proposed by NASA: “a self-sustaining chemical system capable of Darwinian evolution.” But how useful is this really for scientists working on planetary exploration missions? Imagine an astronaut or rover on an alien planet, tasked with searching for life. Do they really have to wait until they can observe Darwinian evolution, which could take generations? Why must evolution be Darwinian? In the world we’re talking about Designer kidsWe can easily imagine new forms of life to which it will undergo Lamarckian evolutionand passes on acquired characteristics rather than evolving solely due to natural selection. Aren’t they considered alive too?
As usual, when considering such questions, we are hampered by our limited state of knowledge. We are still trying to define life in terms of properties we can observe, just as 19th-century scientists defined water as a liquid that freezes at 0°C and boils at 100°C. Only with the discovery of molecular theory did they come to define water as H2Hey.
There is also the problem of N=1. How can we expect to come up with a good definition of life when we only have one example: life on Earth? Even with all its diversity, can we really be sure that life on Earth represents all life in the universe? Can we really rule out the possibility that we’re weird?
Perhaps it is partly a linguistic question. Grammatically, “life” is a noun. But biologically, it is more like an action, more like a process than a thing. The definition of life is similar to that of wind, which describes moving air – a state of being rather than a specific being. Wind molecules are the same as air molecules, but their dynamic state is as well What defines them?.
Maybe we should consult philosophers. The lack of a single accepted definition of life is because there is no comprehensive theory of living systems, says Carol Cleland, a philosopher at the University of Colorado at Boulder. As we search for life on other worlds, we… Emphasis should be placed on anomaliesWhich in some cases may turn out to be alive. This seems to be an appropriate search strategy, especially when we are searching for life as we do no Get to know him. Otherwise, if our search parameters are set so narrowly that we can only search for familiar, terrestrial life forms, extraterrestrial life may be too alien for us to recognize.
Universal checklist
Despite these dilemmas, there are certain features we should expect from all living things. There must be some kind of boundary and imbalance between the organism and its external environment (if there is no difference between you and the dirt around you, you are probably dead!). There must be some external energy to do the work inside the organism. Finally, the organism must be able to reproduce itself.
This last criterion may be the most important. But it raises another thorny issue: Do we call a machine “living” if it is capable of assembling another machine (whether similar or different from it) from raw materials and components? Pass the necessary instructions to continue repeating this manufacturing process? Or should we reserve this term only for the biological life forms that designed these self-replicating machines, even if the designers are no longer alive?
As we head into space, beyond our home planet, we will encounter such mysteries, just as the rise of artificial intelligence raises (sometimes uncomfortable) questions about what we mean by consciousness and even consciousness. Right now, we don’t have good answers. But at least we’re starting to think about the possibilities in a more sophisticated way.
Sign up for Big Think on Substack
The most surprising and impactful new stories delivered to your inbox every week for free.
ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
