I had a thought the other day when rereading some opinions on the question: "are viruses alive?"

This is a big topic in biology. It's normally a question posed to underclassmen in their college biology surveys. At first, it seems rather obvious that viruses should be alive. After all, bacteria and other single celled organisms are the most common form of life. However, here is the argument generally given against viruses being alive:

Living things reproduce. In general, cells reproduce by making a copy of their DNA. Unlike cells, viruses do not have the tools to make a copy of their DNA. But they have found other ways to make new viruses. This is done by inserting virus genetic material into a host cell. This causes the cell to make a copy of the virus DNA, making more viruses.

Many scientists argue that even though viruses can use other cells to reproduce itself, viruses are still not considered alive under this category. This is because viruses do not have the tools to replicate their genetic material themselves.

More recently, scientists have discovered a new type of virus, called a mimivirus. These viruses do contain the tools for making a copy of its DNA. This suggests that certain types of viruses may actually be living.

There are, of course, problems with this definition on a number of fronts. Bacteria of the phylum dependentiae also depend on other cells' molecular machinery to reproduce their genetic code, reproducing similarly to viruses. Obviously there are also a whole host of obligate parasites that are dependant on a host to survive, although they don't reproduce using the same mechanisms as viruses (whereas dependentiae do).

I always came down on the side of viruses being alive. The reasons being that:

A. They reproduce within living ecosystems.
B. They undergo natural selection and evolution, just like living things.

I'm now rethinking this in light of the attributes of memes. Memes also require a host. They exist within the material substrate of human brain tissue, and their instantiation in the material world is a pattern of neurons firing together. Obviously they are obligate parasites.

Memes also reproduce, they jump from one host to another. Other human brains get exposed to a meme through sensory inputs, and the meme becomes instantiated within their brain tissue as well.

Memes undergo natural selection and evolve over time. Thus, memes:

A. Reproduce within living ecosystems
B. Undergo natural selection, just like living things

Memes even have a bit of a leg up on viruses in that they exist within the medium of cells that are clearly living things.

The problem here is that a meme is even more abstract and disconnected from the physical science aspects of biology than viruses and prions. It certainly "lives" in a biological substrate, but it doesn't have RNA or even any set chemical make up. Indeed, the pattern of neurons that make up a meme in a given brain will change over time.

The second problem for memes being alive, is how they can exist in a dormant form, in human texts. The memes of Gnosticism, as actually understood by Gnostics instead of Christian heretic hunters, vanished from human brains with the purging of the Gnostics and destruction of their books in late-antiquity. However, in 1945, when a large collection of these books were discovered in Egypt at Nag Hammadi, the memes were revived. How can a living thing exist in words? This would seem to stretch the definition of living too far.

However, this seems to be the type of "life" Dawkins was thinking of when he created the term. The meme is a new sort of DNA for a new self replicating "thing," that exists in the biological sphere.

Where I think this gets interesting is in comparisons to Platonism. Plenty of people will accept mathematical Platonism, but reject Platonism in other respects. Numbers exist in their instantiation in the physical world. Memes though, seem to open up the prospect of non-mathematical ideas existing through their instantiation in the physical world as well.

Maybe there is something there to tie the physical sciences to the social sciences. As it stands, the gap seems virtually impossible to bridge. It's hard to see how one jumps from neuroscience to politics. The idea of ideas as not just as abstraction, but as being instantiated in the physical processes of their generation as thought, seems like it could bridge this gap. It's almost like a missing link in the chain of emergence.

"Undergoing natural selection," is also probably a weak way to define life. If you read someone like Spencer, everything is natural selection.

I don't have a solid conclusion here. I thought it was interesting and the last topic I saw on this searching was four years old. Hell, I'll make it a poll.