Comparing DNA sequences between our cells and primitive organisms

Student:
Have you been able to work out the oldest kind of gene?

Professor Sykes:
I haven't done any of this work myself but I do know that many of our genes - if you compare the DNA sequence between our cells and other creatures, some of them are virtually unchanged, believe it or not, to really simple creatures.

Fish and even yeast, for example, incredibly we have genes that are almost identical in us as they are in yeast. So you might say "that's incredible, why on earth is that?" but if you think about it, yeasts are cells. They have to do the same thought of things, they have to divide and all that. So genes that are important for say cell division, tell cells when to divide and how to do it, there's no reason for them to change because it's a very similar system in yeast as it is in us. So they don't change. They just stay the same. They don't mutate or if they do mutate, cells can't divide so they become extinct. So these genes, they don't have any reason to change, they don't change. We have many, many genes within us that are, I wouldn't say absolutely identical, but jolly close to genes in what we would consider to be very primitive organisms like yeast and arguably even bacteria.