Yea it is interesting that algae would evolve when it is very well adapted.

It isn’t that it needs or wants to change. This implies purpose. Even though algae is very well adapted as a population, within this population there will be variation and competition. For algae it mostly competes over nutrients and this is why we get a algae boom when there is fert runoff into streams.

So if one algae has a mutation that gives it the ability to get more nutes then it will out compete the others. And it’s genetics will become more prominent in the population.

This is somewhat speculation. I will type something up about how species are created which is probably more relevant that what I just posted.

I am always speculating when we talk about specific examples.
I am also do not have a good grasp of the start of evolution.

I do know that there was an experiment in which two scientists put a bunch of regents that were present in the earth millions of years ago and mimicked the conditions then. Hear low oxygen etc and after a few days they found proteins in the mixture.
So proteins will spontaneously be created, and this is a huge step towards life.