Theoretical biologist here. I consider viruses to define the lower edge of what I’d consider “alive.” I similarly consider prions to be “not alive,” but to define a position towards the upper limit of complex, self-reproducing chemistry. There’s some research going on here to better understand how replication reactions (maybe encased in a lipid bubble to keep the reaction free from the environment) may lead to increasing complexity and proto-cells. That’s not what prions are, but the idea is that a property like replication is necessary but not sufficient and to build from what we know regarding the environment and possible chemicals.

I consider a virus to be alive because they rise to the level of complexity and adaptive dynamics I feel should be associated with living systems. I’ll paint with a broad brush here, but they have genes, a division between genotype and phenotype, the populations evolve as part of an ecosystem with all of the associated dynamics of adaptation and speciation, and they have relatively complex structures consisting of multiple distinct elements. “Alive,” to me, shouldn’t be approached as a binary concept - I’m not sure what it conceptually adds to the discussion. Instead, I think it should be approached as a gradient of properties any one of which may be more or less present. I feel the same about intelligence, theory of mind, and animal communication.

The thing to remember when thinking about questions like this is that when science (or history or literature…) is taught as a beginner’s subject (primary and secondary school), it’s often approached in a highly simplified manner - simplified to the point of inaccuracy sometimes. Many instructors will take the approach of having students memorize lists for regurgitation on exams - the seven properties of life, a gene is a length of dna that encodes for a protein, the definition of a species, and so on. I don’t really like that approach, and to be honest I was never any good at it myself.

They're not compromised of cells, can't self regulate, and can't replicate on their own and other organisms have to do that for them. The last point being important to our criteria for living. I was never taught as a biologist by anyone that they were alive

Worth mentioning: life is a construct created by humans. We decide if it's alive, just like we decided if anything else was alive. There's no definite answer that science can provide on this topic. It can only provide humanity with more facts with which we can contrive a distinction.

Perhaps an artifact from an earlier abiogenesis event that cannibalized itself before our own evolutionary tree started?

I’m no scientist but I’d say, “Do it reproduce? Do it evolve? Do it try to survive? Bruh, it’s alive.”

I’m no scientist though. Just an idiot watching thangs. :p

ok i'm not a biologist but having a cell structure as a prerequisite for defining life sounds very arbitrary to me.

rocks shaped like faces

The rare xkcd I find charming and relatable rather than charming and arcane.

They may not be alive but prions scare the ever living fuck out of me.

I swear Fungi are an alien species, they're so weird

The image is in fact CGI, but yes there are several viruses known as bacteriophages that look like this.

Trying to find this confirmed electromagnetic scan of this phage led me down a truly fascinating rabbit hole about antibacterial phage therapy, taxonomy, and more. Let your curiosity take the better of you on Wikipedia

At this scale we'd be seeing with electrons not photons, and everything would be gold coated. It's unlikely the head would be transparent. But other than that, not bad. False color gets applied to the B&W EM images, which helps.

Rabies is shaped like a bullet!

Artist's view of bacteriophages, viruses that infect bacteria and look like this. They attach to the bacterial wall with these fibers that look like spider legs, and then inject their DNA into the bacteria by contracting the sheath that attaches to the DNA-containing head. They kinda work like a syringe.

Yes, this is a bacteriophage. Truly fascinating stuff I'm lucky to work with every day.

Nah they're a single molecule. While they do have a mechanism to "reproduce", they cannot react to stimuli of any kind, or evolve. Of the 7 commonly accepted traits of life, viruses have 5-6 depending on where you stand with them not being able to reproduce on their own. (In comparison, while a tapeworm or other parasite might need a host, they bring their reproductive equipment with them).

Prions have 1 of those traits. They can't regulate an internal environment as they cannot have one, they lack any kind of organizational trait, they have no metabolism (the other one viruses lack), they do not grow, they don't adapt to their environment, and they do not respond to stimuli.

A digital thermometer has organization and responds to stimuli, so it's more alive than a prion.

I knew iOS was poison