Although at first glance my question is perhaps better suited for a space exploration or sci-fi forum I looked and felt this forum was more appropriate.

What makes plants and animals edible and allows us to gain nutrition from them? If life evolved separately from life on earth would any of it be edible to us or to any other creature that evolved on this planet.

My question is not about stuff being toxic, its about if anything other than life on earth, would be digestible? Do we need to evolve side by side with our food? I know of convergent evolution, that may make things look similar, but is there something at a cellular level that makes things edible. Does everything edible have DNA?

I don't have an academic background in biology so apologies if this question sounds silly. It's been bugging me for ages. My gut feeling tells me that nothing will be edible but I don't have any science to back that up.

I'm a vegetarian so I'm not just thinking about hunting and eating aliens either!



closed as primarily opinion-based by rg255, AliceD, Remi.b, MattDMo, kmm Apr 22 '16 at 23:58

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Given that we have pretty much no idea what life on other planets may be like it is nearly impossible to answer this question in a non-opinion based way $\endgroup$ – rg255 Apr 22 '16 at 17:34
  • $\begingroup$ Amino acid chains are found in carbon rich meteorites so that gives a clue. $\endgroup$ – Graham Chiu Apr 22 '16 at 23:59

Short Answer- No, chances are negligible.

Long Answer- Digestion is a chemical process which is mediated by enzymes. Enzymes are highly choosy molecules so that they only perform the work they're made for. In digestion, enzymes like proteases (for breaking down proteins), lipases (for breaking down lipids), amylases (for breaking down starch), DNAses (for breaking down DNA), etc. are involved. For example, amylase is specialized to break down polysaccharides (carbohydrate polymers) into mono/di/tri/oligo-saccharides. See this from wikipedia:

The α-amylases are calcium metalloenzymes, completely unable to function in the absence of calcium. By acting at random locations along the starch chain, α-amylase breaks down long-chain carbohydrates, ultimately yielding maltotriose and maltose from amylose, or maltose, glucose and "limit dextrin" from amylopectin.

And this image from here:

amylase working

Lets forget the "completely unable to function in absence of calcium" part as it is out of the scope of this question. But it is necessary to know how specialized enzymes are to answer your question. They are so specialized that amylase can break starch, but not cellulose. See this image:

starch, cellulose and glycogen


You must have noticed, in the diagram above, the minute difference between starch, cellulose and glycogen (BTW glycogen is another polysaccharide), but even that difference is enough for enzymes to tear apart one and pass on the other molecule.

The above explanation was necessary to tell why the answer is no. If we eat something, enzymes are needed to break it down. But if enzymes cannot recognize something, then they can simply not work on it. So, if you even want to eat space grass, forget about being able to digest it. Because even if we confirm that life on earth came from space through meteorites billions of years ago, then also during this time period of billions of years both that life of space and this life on earth would have evolved so much that they might not match, even chemically!

Hope this helps. Tell me if you want any more details :)


Absolutely! The only limitation animals face on eating substances or objects is the size of the opening to their oral cavity, so if there is something on another planet that will fit in your mouth then you can definitely eat it.

Whether one would be able to derive energy from the exo-material is an entirely different question.


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