My guess is that they develop randomly out of free will just like a mutation would out of genes. Someone developed moral values because of free will and this started a snowball effect which caused others to see it too. By nature, humans are generally compassionate and empathetic. Sociopaths or Psychopaths generally don’t have moral values, that’s something important to note, people with brains that work like 9/10 people (1:10 I believe is the statistic of sociopaths, feel free to disagree with that as I’m not sure it’s entirely accurate and I’ll edit the statement to the correct information if it’s wrong) will develop moral values based around the society around them, at one point someone developed it of their own free will and this idea grew. Empathy and compassion in older times also equals friends and allies which equals more confidence in yourself given you now have protection and can survive easier knowing you have allies. So it could also be that it developed as a survival instinct.