Sometimes when you are trying not to think about something it keeps popping back in your head you can't help it you think about it and think about it and think about it until your brain feels like a squashed pea.
Not one of your pertinent ancestors was squashed, devoured, drowned, starved, stranded, stuck fast, untimely wounded, or otherwise deflected from its life's quest of delivering a tiny charge of genetic material to the right partner at the right moment in order to perpetuate the only possible sequence of hereditary combinations that could result -- eventually, astoundingly, and all too briefly -- in you.