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Comment by jeletonskelly | Hacker News Reader

There's an unbroken chain between everything current living thing and the first living thing, so don't we share DNA with well... everything?

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Given DNA is quantised into just four nucleotides -- and I suspect that there is no organism that uses, say, just three -- then wouldn't your statement be trivially true? That is, pick a 1mer of a random nucleotide (A, C, G or T) and there you go.

What I suspect you're getting at is, rather, if our DNA contains virus DNA, then presumably that virus' DNA also contains the DNA of organisms it encountered (using the same mechanism), etc. Thus, there ought to be an unbroken history -- albeit probably highly corrupted from successive adaptive mutations -- in our DNA to the first living thing. This wouldn't necessarily be everything, though; just everything we've assimilated.

Yes, that's sort of what I'm getting at with that leading question. If we accept evolutionary biology then a headline like this wouldn't be all that surprising. All living things converge at the root.

> If we accept evolutionary biology then a headline like this wouldn't be all that surprising.All living things converge at the root.

That doesn't mean that everything has already been "invented" at the root.

> That doesn't mean that everything has already been "invented" at the root.

Exactly. The "classical" view of evolutionary genetics is that new genes develop by mutation, are favored (or eliminated) by natural selection, and exchanged only within the same species by interbreeding. So the family tree of life is a map of how closely organisms are related, and they would share a gene only with the nearby branches of the tree descended since that gene arose.

We have long known that the simple model is not complete, prokaryotes (bacteria and archaea) exchange lots of genetic material outside their own "species" (trickier to define for bacteria in any case), but it is becoming more widely recognized that lateral gene exchange happens a lot in all organisms.

A recent popular book on the subject is "The Tangled Tree: A Radical New History of Life" by David Quammen.

What this article is saying, though, is stronger: It's not just convergence to the root, but also branch merges. While those branches will converge to the same root, they may have diverged significantly (such that today, we recognise them as from totally separate organisms).

Yes, generally speaking, but there are genes that were evolved on branches after they separated from ours. We don't produce chlorophyll even though we share some DNA with plants.

Imagine in languages: Indoeuropean languages share a common ancestor, but we can say that suchandsuch word is originally from some language and then adapted into another language and used for potentially different meaning.

There's an unbroken chain between everything current living thing and the first living thing...

I don't think that's an established fact at all. DNA is a very complex system so it's reasonable to think that simpler systems predated it. Not that it affects your reasoning at all, since every current living thing that we know of does use DNA.

I do believe there's an abstract principle that we share with anything that sustained its structure. Not a specific thing like a set of genes but the underlying set of chaos-avoiding rules that makes living forms living forms.

These rules are the laws of thermodynamics.

I thought we were the optimized thermodynamics dual/dampener. Our system fight to slow entropy.

The RNA world hypothesis proposes that self-replicating RNA molecules proliferated before DNA, which would be that simpler system as it doesn't require complex protein machinery.

The truth of that statement is presently unknown. All that's known for sure is that all life we've found so far shares a common ancestry. It's possible there were multiple abiogenic sources of life and the one we see now just out-competed everything else. So maybe the first living thing has no ancestors alive today.

What's the argument that life couldn't have arisen multiple times? If the conditions for spontaneous generation existed on the primordial Earth, why wouldn't they have held in more than one place and why couldn't genesis have occurred more than once?

There is no consensus about how life originated on earth. It's perfectly possible that life has arise multiple times.

And how do we come to share genetic code and genes with the most distant organisms?

Refer to the Singularity & Big Bang some 13 billion years ago, when we and everything in the (known) universe were all crunched together for just the smallest possible length of time....

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