what's sex for?

the Red Queen's Race exacts a fearsome price
as ev'ry sword as cause spurs shield effects
and ev'ry virtue brings its hidden vice
compelling us to cast our dice at sex
parthenogenesis would rule the day
if not for pathogens and parasites
but if the hosts' genomes were all the same
each plague might devastate them in the night
and so we throw out half our genes each round
and trust the ones we love to do the same
reshuffling makes a deck that's new and sound
to let our kids survive to play the game
our genes live on 'though as their hosts, we die
and Darwin speaks to "how" but never "why"