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Comment by KineticLensman | Hacker News Reader

> The reason aliens are likely to be made out of DNA and have cells is simply that those things tend to naturally come to exist in our universe.

I think you are confusing carbon-based life with DNA-based life, for which N=1, the Earth. There is absolutely no evidence that DNA exists anywhere else. I'm prepared to accept the argument that carbon+water is a good basis for life, but this does not inevitably lead to DNA-based replicators.

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Ha, interesting proposition. What do you think would be the alternative to DNA? I'm curious as I'm a complete layman. Intuitively, I'd think that a self replicating life form will need something to carry it's program, and this is what DNA is. Alien life might use different molecules to carry that program, but conceptually it would be the same, no?

I'd even go as far as to say that DNA arose out of the fact that carbon based chemistry is good for life (we see N=1 case at least), and once we accept carbon based chemistry, amino-acids are the next optimal step, followed by something like the DNA to program the construction of proteins for amino acids.

Again, I'm just a layman so it'd be nice to know the views of experts in this area.

> I'd think that a self replicating life form will need something to carry it's program,

Well yes, for sure, a replicator needs some sort of 'program', and if you go for carbon+water, amino acids are a good bet.

> and this is what DNA is

Yes, on Earth. But the actual horrendously weird and complex molecule Deoxyribonucleic acid is not the only way of implementing such a program. Check out a text such as 'How Life Works: A User’s Guide to the New Biology', by Philip Ball to see why I'm being picky here.

Among other possibilities, RNA. I don't remember off hand why RNA doesn't work as the primary store of data, maybe not stable enough?

I think that the only thing that is inevitable is complexity changing over time. My first thought was maybe there could be a more distributed sort of "program", but maybe we already have that - either evolution itself, or if evolution somehow isn't inevitable, something that bootstraps or otherwise facilitates it.

Imagine yourself existing on a microscopic scale, with your current consciousness intact. You'd look into the 'sky' and see an organelle membrane or nuclear envelope... what would your concept of the "program of life" be, while existing adjacent to DNA itself? Would this activity look a bit like some of the natural processes we witness and take part in on Earth?

DNA is really complicated. There are probably a bunch of other polymers that could fill the same role.

N=1 is a whole lot larger than N=0, eh?

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