What do you believe has been the most important scientific discovery/breakthrough?

Question: What do you believe has been the most important scientific discovery/breakthrough?
- Keywords:
  breakthrough,
  discovery
Asked by Izzy to Anna, Hayley, Iain, Rebecca on 15 Jun 2015. This question was also asked by 649yttc25.
- Iain Bethune answered on 15 Jun 2015:
  
  I think that James Clerk Maxwell’s theory of Electromagnetism was the single most important discovery, as without it there would be no radio, electronics, computers…
- anon answered on 15 Jun 2015:
  
  I think it always depends on the field you work in – there are so many different important discoveries which has helped the various sciences progress massively. I think Iain’s suggestion is a very good and important one for many disciplines, though!

Question: What do you believe has been the most important scientific discovery/breakthrough?