Those games where you fuse elements to create higher ones can be really addictive... To prove it, here is Human Evolution, a life evolution simulator where you have to try to recreate the evolution of life on Earth.
From DNA chains to what will come after human beings
You start the game by fusing DNA chains. From there, you will take a step to unicellular and, gradually, multicellular beings that live in the water until you manage to crawl out to the shore... And so on, until you reach human beings and beyond. You can even get a glimpse of post-human evolution reminiscent of H.G. Wells' The Time Machine (now, there is a spoiler if there ever was one!).
Evolution ends when you have cyborgs and intelligent robots. Still, the fun thing is that you don't always get to that point in the same way: at one point, you can decide which evolutionary line you want to follow, whether that of humans or that of other living beings such as reptiles, birds or mammals.