Khandro, I didn't say that a human is 'constant and unchanging' you are trying again to put words in my mouth. A wave can alter in amplitude and length but it is still essentially the same wave. Much if not all of nature is dynamic albeit sometimes on a very long time scale. As for examples in nature just open your eyes, look at the sky, look at rivers, look in wikipedia. If you cannot find anything come back to me and I will give you examples
As for your quote from Heraclitus, though a glib philosophical point, it can be argued that the man and the river are not their material constituents but the phenomenom that they are. That is why rivers are marked on maps and humans have an identity from birth to death. That is to say a river is not the water in it and a man is not the food he eats.