There is no doubt that if he had not solved the nitrogen-fixing problem, someone else would have, and it is certainly possible that someone else would have pushed the use of poison gas into practice. It is also generally simplistic to claim that any one thing greatly prolonged the war. 'Great men' and 'pivotal event' historiography is a simplistic way of looking at the past, but nevertheless, it is a simple historical fact that he was the person who did these two things, and the case for nitrogen-fixing extending the war is better than most other 'but for...' stories.
I think people take special people for granted. You can't say, for certain, that anyone would have figured out the nitrogen fixing problem _in a period of time when it would have been effective to have done so_. The entire world could have been blown up before someone came along to figure it out.
The world has yet to churn out another mind quite like Einstein's, that flips convention on its head, or opens up humankind's collective knowledge by an order of magnitude. Special people, like Einstein, this man, Norman Borlaug or Ada Lovelace, I think, may have just been the right people at the right moment.
You are right; I cannot say for certain that someone else would have solved the nitrogen fixing problem in time to save humanity from global starvation, but for it not to happen, it would have required a lot of chemists to all not perform the sort of experiments that chemists are trained, employed and choose to do.
Having read somewhat widely, as a kid, about the history of technology, I was struck by how often several people were working independently on the same ideas at the same time, but that is not so surprising once you realize that the timing is often determined by when some prerequisite knowledge became available, or some prerequisite capability was mastered. Einstein stands among the most original thinkers of all time, but even he was standing on the shoulders of people like Heaviside, Fitzgerald and Lorentz (and Maxwell, of course) - yet the first three, at least, are invisible in popular historiography.
I disagree. I think there are many minds that would be capable of what these people did (not everyone, certainly not myself, but thousands of people alive today).
It is a case of having the right person in the right place at the right time, Einstein would have not had his theories had he been around 20 years earlier, or if he had not had the opportunities that he did. And if he had not been around then I think it would have been others. It is about the environment, Calculus was developed by two people simultaneously.
As to why we haven't had someone who has done this, well who's to say that we haven't and they are just overlooked? Or that greater capital expenditure it has to be groups of people (finding DNA, cloning, Graphene, etc). Or that there has simply not been the right environment.
Where do you draw the line? Is John von Neumann in the list? What about Feynman? Do you include Go or chess players that changed the game? What about Castro who successfully kept independence from the superpower next door? Linus Torval has made amazing contributions to modern computing by BDFL. What about Shannon, the father of information theory, or the men behind RSA?
Draw a line between these and choosing what field of study or what kind of change to the world counts to make a "special person" changes the number of special people dramatically.
