Some 20 years ago, biologist Richard Lenski, of Michigan State University took a single Escherichia coli bacteria and then kept on feeding it the glucose
one bacteria lead to many and he made 12 different populations that he kept going for 20 years
but then, at about 31 thousand 500 generations of bacteria later, he noticed Escherichia gained the ability to metabolise citrate
the other populations didn’t develop this
now, being careful, Lenski has an archive of every 500 generations stored, so he could replay the process and see if the later generations would develop the same ability (mutation)
the result was, only the original population developed the same mutation when replayed
read more about it here