A feather, a dinosaur scale that has been modified and which now allows a bird to fly as well as keeping it warm.
The question is how the modification has come about.
Some would have it that the feather is the result of intelligent design whereby some intelligent force has modified the scale with the clear intent of producing a structure to provide insulation and to enable flight.
Others would argue that the feather is the result of natural selection whereby favourable genetic mutations accumulate over time. In this scenario there is no design involved as there is no intended outcome.
I know where I stand on the issue but I am happy for those of a different persuasion to be wrong! However it came to be, the feather is a marvellous and beautiful object.