[tortoise]

I was taught in high school and college that although viruses can replicate that there is really some debate as to whether they are really alive.

That is because "aliveness" is a continuum and not a binary state if evaluated in a strict and rigorous fashion, though we tend to treat "alive" as a binary condition in common usage.

There is almost an unbroken chain of self-replicating molecular entities in nature starting with simple molecules all the way up to big critters like humans. Viruses occupy one part of that chain of molecular complexity right around the gray area where we stop treating them as complex molecules and start treating them as macro-systems as a matter of functional complexity. "Aliveness" is a continuum and putting the breaking point at any one point in the chain of complexity is arbitrary, as the entities on either side of any breaking point will be nearly identical in nature.

[metmom]

OK, that makes sense. I thought I remembered it like that but it's been a number of years.

[metmom]

So this is along the lines of the concern about nanotechnology and grey goo only living cells are not required for replication of the nanorobots? Nanorobots would not technically be alive but could be self-replicating. So, they would be a kind of environmental virus?

[Anthem]

There is almost an unbroken chain of self-replicating molecular entities in nature starting with simple molecules all the way up to big critters like humans. Viruses occupy one part of that chain of molecular complexity right around the gray area where we stop treating them as complex molecules and start treating them as macro-systems as a matter of functional complexity. "Aliveness" is a continuum and putting the breaking point at any one point in the chain of complexity is arbitrary, as the entities on either side of any breaking point will be nearly identical in nature.

Do you have any references for further reading? Thanks.