crushing biology

i am no biology expert, but as far as i can remember from biology class at school, all creatures are biologically designed to focus on re-production - and whether their methods of attraction to secure a mate are through flashing their coloured plumage, emitting intoxicating chemical secretions or ripping the mate's head off (sucks to be male praying mantis!!), they are designed to try and perform these acts as best as they possibly can so as to secure reproduction and the survival of the species...

why then, when humans are attracted to another of their species do we (or just me??) not perform at our best, not show our best colours, but turn into bumbling uncomfortable idiots??? it does not bide well for the survival of the species!