Why do humans bury their dead?
Some theories:


Dead bodies died of something. In the earliest ages these were generally infection. Burying them protected us from something that could kill us too. This is also why we would be evolutionarily programmed against cannibalism
They make great fertiliser. Burying waste, dead animals etc resulted in the growth of plants etc which not only food we could eat but animals that would then eat the plants we could kill and eat. 
Dead bodies are unpleasant. They stink and so we would want to get rid of them. Also they would attract carnivores which are likely to target humans too


All these would be evolutionarily advantageous so any cultures practising burial would be likely to survive and pass on those customs. Whether this is genetic, that's open to debate because I'm not sure.