Plants know their kin, too:
The indefatigable blogger hbd chick found this reference to an article (Susan A Dudley and Amanda L File Kin Recognition in an annual Plant Biol. Lett. 2007 3, doi: 10.1098/rsbl.2007.0232, published 22 August 2007) You can see it for free.

It turns out that the roots of a plant can tell whether another root is from the same plant.  That’s getting pretty close to self-awareness.  But the point of the article is that plants raised in pots with strangers will increase their root production.  But when they are in the same pot with siblings they do not compete so strenuously. 

It isn’t reproduction.  It’s more like altruism directed toward kin.  That certainly produces an overall selective advantage.  It would be most odd if plants could respond to kin and humans could not, I am thinking.

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