How did Evolution produce Symmetry?

I think in general the idea of necessity applies also to
plants.They don't move and don't have a head-tail division, but are
subject to gravity and have a top-bottom division (roots down,
stems up). Even leaves have an underside.

If the third eye would be beneficial why didn't
god put one there?In terms of a body-plan one could claim ANY form to indicate
a designer, since a designer is free to do anything they
wish (given sufficient resources).That we see a consistency of form across the continents would
tend to lean away from a designer rather than toward
surely ....