How can evolution explain body symmetry?

There is a sane explanation for this, Crash.Symmetry is expensive to produce, slight asymmetries are significantly easier to make - which is why symmetry is so universally sexually attractive (it's not only humans, it's also birds, cats, dogs, mice, rats, dolphins and monkeys and probably a whole load more animals they haven't tested it in). Thus more symmetrical individuals are, in general, more gentically fit as well as having more enviromentally preferable lives (childhood illness, and malnutrition both produce asymmetry). Thus what the girls are smelling is not symmetry but instead fitness that itself produces symmetry.

And, interestingly, it has been suggested that a reversed retina is a better design for a flat, or cup, eye due to improved directional capability.