so I just spent these past few days evolving my already evolved small grey fish which are based on the standard four celled smart swimmer. the reason why is bc they swam by only moving their tail straight and to the left. by best guess for this might have something to do with the front half of the organism being asymmetrical. which usually happens with the standard four celled smart swimmer due to them looping around unreachable food and starving to death if they are symmetrical. so that might have influenced the fish even with the addition of a tail. anyways now the tail moves more so left AND right which was what I was looking for and was very annoying to try to evolve due to them always wanting to default to left and straight movements.