It's impressive how much knowledge humans have managed to gather considering we were not given any sort of instruction book.  If you think about it we had to figure a lot of stuff out through trial and error.  I always find this especially crazy when it comes to poisonous substances.  We didn't know they were poison until some poor sap consumed them and suffered the unpleasant consequences.  "Oh dear, Clancy just ate that colorful mushroom and then died a horrible, painful death.  Perhaps we shouldn't eat those."  The worst part is if Clancy had that mushroom as part of a much bigger meal, nobody might have pieced together at first that the mushroom was at fault.  It probably took multiple instances of people dying before the culprit was identified.  I'm just saying there are a lot of unsung heroes among our ancestors who took the proverbial bullet so we know not to drink drain-o.