I don't know if allergies are really new. When I was young the little boy next door had quite severe asthma (I don't know if allergies were involved, but allergic asthma is the commonest sort in children); and the little girl across the road died during an attack.
plants share allergens ( one in all in sort of - this is AB)
darwin and all that - once a stationary plant has solved a problem, the solution ( protein, DNA ) will persist and not get lost
and yes you can do a family tree of plants using this