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Consider the hypothetical case that we encounter alien life and it is based on the same chemical foundation as terrestrial life (amino acids, nucleic acids, etc.). Would it be reasonable to expect the same chirality as terrestrial, a 50/50 chance of it being the same, or some intermediate probability?

In other words, is chirality truly random (50/50), are the forces which influence it favouring one choice while not excluding the other, or is one choice sufficiently favoured that the other will be inevitably extinguished?

Or, is this a question which can only be answered by actually finding and cataloging life of non-terrestrial origin?

Anthony X
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Who knows?

It seems like it would be random. In that case there would be a 25% chance to have the same chirality choices, since both DNA and proteins each have their own chosen direction.

There is a theory that weak nuclear decays, which have a preferred handedness, could have preferentially destroyed organic molecules of a particular handedness, resulting in the choices we see today. It is a very small effect, but accumulated over time might have been what tipped the hand, so to speak.

Mark Adler
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  • Not sure I understand the 25%. I thought that chirality of DNA and protein would be interdependent - only one choice for both, not two independent choices. – Anthony X Jun 28 '15 at 02:45
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    DNA is right-handed and amino acids are left-handed. I am not aware of any reason that they need to have opposite handedness. They could just as well both be right or both be left. – Mark Adler Jun 28 '15 at 05:06