Do you know what causes the genes of different organisms to evolve and change?

Question: Do you know what causes the genes of different organisms to evolve and change? If you do not, is there anything else you can tell me about the evolution of different organisms?
- Keywords:
  evolution,
  gene,
  organism
Asked by Keshawn Ladanian to Sharon on 8 Mar 2017.
- Xueyuan Jiang answered on 8 Mar 2017:
  
  The evolution of different organisms has a lot in common. They look different to our eyes because evolution results from a lot random events.
  
  Two major forces are worth mentioning: mutation and selection. Mutation is the random error that happens then DNA replicates. Hmm, this may sound ridiculous, but those mistakes make the gene pool more diverse, and is actually good in the long run. Selection, on the other hand, decide which type of gene is more fit in the current environment.