A fiftieth birthday encourages one to look both backwards and forwards. Could the behaviour of the infant, in the first year or two of life, give a glimpse of the adult to come? And can the present state of that adult be used to make predictions for the future? Here we refer not to the existence or eminence of the Journal of Fluid Mechanics, both of which seem to us to be perfectly secure, even with the onset of electronic and open-access publishing, but to its content and the nature of fluid mechanics itself. To give substance to our reflections we have looked through volumes 1 and 2 (May 1956 to August 1957) and compared them with the three most recent volumes to hand at the time of writing, numbers 532 to 534 (June to July 2005). The total number of pages in each case was almost the same, though there were 80 papers in the first two volumes and only 49 in the recent three.