"Indeed, in its endeavour to explain and predict particular events, which it does so successfully in the case of relatively simple phenomena (or where it can at least approximately isolate ‘closed systems’ that are relatively simple), science encounters the same barrier of factual ignorance when it comes to apply its theories to very complex phenomena. In some fields it has developed important theories which give us much insight into the general character of some phenomena, but will never produce predictions of particular events, or a full explanation—simply because we can never know all the particular facts which according to these theories we would have to know in order to arrive at such concrete conclusions. The best example of this is the Darwinian (or Neo-Darwinian) theory of the evolution of biological organisms. If it were possible to ascertain the particular facts of the past which operated on the selection of the particular forms that emerged, it would provide a complete explanation of the structure of the existing organisms; and similarly, if it were possible to ascertain all the particular facts which will operate on them during some future period, it ought to enable us to predict future development. But, of course, we will never be able to do either, because science has no means of ascertaining all the particular facts that it would have to possess to perform such a feat."