A beginning

If by "lying around", you mean "performing no useful function", then yes, this can happen.Primates have the non-functional remains of a gene for making vitamin C. The loss of it was no loss to monkeys, 'cos they eat fruit, and so they get plenty of vitamin C in their diet: so there was no selective pressure against the defective copy of the gene. If monkeys had had to eat the diet of a nineteenth century sailor instead of fresh fruit then the first such monkey would have died of scurvy and the broken gene could not have spread.I hope this helps.

"By chance" is a summary too far.For example, you will know what eventually happens when we introduce a new antibiotic into our arsenal. Eventually, the bacteria we're targetting will evolve resistance. Now if someone said that this was "by chance", this would be a bit odd. We'd answer: "By chance? It was caused by the introduction of the antibiotic, we predicted that this would happen, it was not a coincidence in any way."Saying that "evolution happens by chance" is an ambiguous statement, like saying that "a lion is a cat", without saying if you mean the species Felis cattus, the genus Felis or the family Felidae. But saying "not by chance" is wrong too, just as it is inaccurate to say that a lion is not a cat.In order to say something unambiguous, you have to go into more detail, and say: "Lions are of the family Felidae; evolution works by selection acting on random variation."Edited by Dr Adequate, : No reason given.