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Comment by TangoTrotFox | Hacker News Reader

This is the thing I also always wonder about. Consider that about 60% of a banana's DNA is shared with us. And for cats it's 90%. That's just really stupefying to think about. But the more important point here is that I think it is literally impossible for us to even imagine what life that had no genetic similarity to us would even begin to be like. We just have no basis for comparison whatsoever since we are all so closely related.

Though yeah, genetic similarity implying exogenesis would also be an equally interesting result. Would that similarity be organic/natural in nature, or might we just be some species' lab experiment? Perhaps they seeded us with their same genetic origins to discover more about their own evolution and development. This is an experiment I'm certain we'll eventually carry out ourselves. So many interesting possibilities.

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So there's two high-confidence bets we can make about alien life:

(1) They will probably share huge swaths of the basic chemistry and machinery: proteins, sugars, starches, fats, and even more surprising things like cell walls and digestive acid and (something like) DNA. The building blocks of life are basic chemistry, and are some combination of "the simplest possible molecule that can do a thing" and "things that arise naturally from inorganic processes".

(2) There will almost certainly be 0% overlap in terrestrial and alien DNA, even assuming aliens use DNA and use the same four amino acids to encode their DNA and even assuming they have identical proteins and cellular structures. This is because the encoding from DNA to proteins is more-or-less arbitrary, and determined by both the exact cellular machinery used to turn DNA into proteins and by our genetic history. Even in our own cellular machinery, different DNA sequences can code for the same protein, so you can encode any individual protein in a bajillion different ways. The only real reason for to different organisms to share any common DNA sequences is because they both derive from a common ancestor. If our DNA and alien DNA overlap in any meaningful way, even with the tiniest of percent, it's basically conclusive proof of exogenesis of some sort.

So basically, it is very likely we'll be able to eat aliens (probably no more or less likely than how likely it is you can eat any particular plant or animal on Earth, to be honest), and almost impossible that we could ever hybridize alien and terrestrial plants and animals.

I think it goes further than that, that alien and native lifeforms will probably be toxic to one another. All life on this planet evolved in tandem, and have some of the same basic compounds for life, so there are few toxic interactions between life forms, excluding those evolved for defense (and even then there are exceptions, plenty of plants contain. And even then there are plenty of exceptions. But lifeforms from a completely different evolutionary line may use completely different proteins for basic functions. Even using the same proteins but of the opposite chirality could result in toxic reactions.

I think that even if we found alien life that evolved and developed on a planet much like ours, and used the same amino acids, metabolic processes, and cellular structures, the odds are high that contact with them would result in toxic interactions.

You've got to weigh "we didn't evolve to specifically eat it" against "it didn't specifically evolve to prevent us from eating it". I'm not sure we'll get an answer to which is a bigger factor unless we find some xenobiology and take a bite.

A lot of digestion is pretty elementary, and built upon our stomachs' acid bath -- proteins go in and are unwound and broken down. Most foods that cause problems later down the line contain a protein that both (a) is resistant to the stomach acid, and doesn't break down before hitting the intestines and (b) causes a problem when it hits the intestines.

Barring that - or incorporating elemental poisons like arsenic at levels we can't cope with - I'd personally bet that if you charred a random alien critter over a fire and wolfed it down, it's not crazy that your stomach acids would break down anything that survived the fire and would otherwise harm you, and you'd be able to extract a reasonable mix of sugars, fats and proteins from what you'd ate.

It's not impossible that an entire planet would have some proteins common to all of their lifeforms that both (a) didn't break down easily when cooked or digested and (b) were incredibly lethal to terrestrial life, but there's no ab initio reason to think they would or wouldn't, one way or the other.

The stomach isn't a perfect barrier, there's always something that gets through. If it didn't we wouldn't be able to take drugs orally. Our bodies have an entire subsystem devoted to processing compounds that made it through the main digestive system into the blood stream. The liver is dedicated to metabolizing these substances, in a process literally called "xenobiotic metabolism".

Sure, the odds of a particular compound found in some alien lifeform having a toxic interaction with our bodies is small, but I consider the odds of one of the hundreds of thousands of different types of compounds in that lifeform having a toxic interaction is on the higher side.

Oh, and to be clear, by toxic interaction I don't necessarily mean a poison, per se. It could also have a carcinogenic effect, or if the compound is common enough in the creature and undigestable through the stomach and intestines it could overload the liver, etc.

Yeah, not a perfect barrier, but if it's good enough that I'm not poisoned, do I care? I eat lots of delicious food that doesn't digest optimally.

As for carcinogenic effects, well, depends on what the timelines and cancer-rates you're talking about look like. We eat lots of things on Earth that are mildly carcinogenic over a lifetime, and the fact they are doesn't really stop us.

I wonder if some of the early core functionality such as replication, splitting, energy generation, etc. only has a few simple and effective possibilities? Are there any really simple RNA/protein patters that almost just have to occur from a statistical/mechanical view?

> They will probably share huge swaths of the basic chemistry and machinery: proteins, > So basically, it is very likely we'll be able to eat aliens

Their proteins may be folded in the opposite direction though. That would make things difficult.

Do you mean from a digestive standpoint or are you thinking prion diseases?

But how quickly did they get started in that case?

I mean, the ago of the Earth is quite a nice chunk out of the timeline since the Universe got started.

200,000 years ago we did not exist as a species.

2500 years ago stabbing each other with iron weapons was literally cutting edge technology.

In the past 200 years we have invented: production automobile, airplanes, space flight, launched probes into interstellar space, computers, the internet, ... We have discovered relativity, quantum mechanics, galaxies, ...

Assuming we are able to survive, imagine where we'll be in 200k years. Actually you can't. It's just impossible to even begin to try to imagine that. On that scale we'll likely have even begun to experience evolutionary speciation as we settle different regions of space and end up with extended periods of relative isolation.

And now consider that this entire timeline is but 400k years. That's not even a blink in the eye of the cosmos.

It took billions of years before complexity started. We don't even know if that is a long time or a short time. We may be among the first.

Absolutely. The point I was making there is that imagine there was another perfect clone of our solar system that was identical in every single way and its timeline was 99.995% identical to ours. Intuitively you'd think that they'd probably be at, more or less, the same point in their development. But that 0.005% is the difference between between glorified monkeys and widespread civilizations launching objects and people into space. And if we add another 0.005% to where we are now, everything we know leads us to believe that the change will be even more extreme since our current technological trajectory remains on a very sharp exponential curve upwards with no reason to expect it to end. As an aside these numbers are also based on the age of the Earth. Looking at the age of the universe would probably be more reasonable and would lead to even more extreme results.

Hm, fair enough. We just don't know a great many things. :)

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